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Rice research for food security and poverty alleviationProceedings of the International Rice Research Conference Session 1: Increasing Yield Potential in Irrigated Rice: Breaking the Barrier
Increasing yield potential in irrigated rice: breaking the yield barrier A stagnation in increases in rice yield under intensive crop management has been recognized in recent decades, especially in tropical dry-season rice. To break the current barrier to the yield potential of rice, it is necessary to identify yield-limiting processes and associated traits, and to quantify their genetic variability. For this, a brief review was made on previous studies on yield formation processes of rice and their genetic variability. The results of our recent experiment in Kyoto, Japan, indicated that the most critical growth attribute for rice yield under intensive management is crop growth rate (CGR) during the latter half of the reproductive period (15 to 0 d before heading). The CGR at this stage critically affects final spikelet number by regulating spikelet degeneration, potential single-grain weight by determining husk size, and grain filling by forming active sinks and determining endosperm cell number at initial grain filling. A considerably large genotypic difference existed in CGR during this period and, hence, in yield; however, higher CGR and yield were not necessarily associated with higher leaf N content. A remote-sensing technology for evaluating canopy diffusive conductance (gc) was developed on the basis of simultaneous measurements of the temperature of sunlit and suddenly shaded canopies. The gc obtained by this method for various genotypes at midday in the latter half of the reproductive period showed a significant linear relation to their CGR and yield, which suggests that gc can be an effective criterion for selecting high-yielding genotypes under field conditions. The existence of a considerably large genotypic difference in gc, together with its rapid evaluation by remote sensing, may encourage efforts to break the barrier to increases in yield potential in rice by breeding inbred and hybrid cultivars having a wide genetic background. Closing the rice yield gap for food security Dat Van Tran The Green Revolution has enabled rice production to meet the demands of the growing population. Since 1990, however, rice production has increased at a lower rate than the population. This deceleration in the growth of rice production is a cause for concern in terms of world food security. It has been the topic of numerous reviews and several rice scientists have alerted those concerned of the risk of a pending food crisis. Yield gaps can still be observed in several countries, while evidence of a productivity decline in intensive rice production has been increasingly noticed both on research stations and in farmers' fields. An increase in rice yield can lead to improved farmers' income and food security. Because of the complexity of this problem, different points of view exist regarding the possibility of narrowing yield gaps as a tool for increasing rice production. Several experts believe that yield gaps in favorable rice ecosystems are not significant for improving rice yield potential. Others believe that large and exploitable rice yield gaps still exist. In 1998, the average rice yields in 81 countries were less than the world average yield of 3.8 t ha-1, indicating the existence of yield gaps. Also, progressive farmers usually obtain higher yields and more profits than ordinary farmers, indicating the presence of knowledge gaps. The yield gap in rainfed rice, which is usually larger than in irrigated rice, suggests the potential for increasing rice production. Closing the rice yield gap aims not only to increase rice yield and production but also to improve the efficiency of land and labor use, reduce production costs, and increase food security. Various factors cause exploitable yield gaps in rice, such as physical, biological, socioeconomic, and institutional constraints, which can be effectively improved through participatory research and government attention. In practice, yield gaps are classified into agronomic gaps, socioeconomic gaps, institutional gaps, and mixed gaps according to constraints in improvement programs. The narrowing of the yield gap is not static but dynamic with technological development in rice production, as the gap tends to enlarge with the improvement of the yield potential of rice varieties. This requires integrated and holistic approaches, including appropriate concepts, policy interventions, understanding of farmers' actual constraints to high yield, deploying new proven technologies for production and postproduction in an integrated approach, and adequate institutional support to farmers. Development of the new rice plant type and advances in research on breeding for super high yield Chen Wenfu, Xu Zhenjin, Zhang Longbu, and Yang Shouren The history, present status, and research trends of breeding for super high rice yield are reviewed and analyzed comprehensively in this chapter. We believe that, even after two major breakthroughs, one through dwarf breeding and the other through the use of heterosis, rice yield has remained stagnant for a long time. The third breakthrough in yield potential is expected to be realized by combining the ideal plant type with growth vigor. Research findings have shown that increasing the biological yield is the foundation, whereas optimizing yield components is the precondition for breaking the yield barrier. Results have also indicated that an effective way to develop super rice lies first in developing the new plant type and strong vigor by crossing indica with japonica subspecies, or crossing geographically distant varieties, and then consolidating the two advantages by optimizing the combination of desirable traits via multiple crossing or backcrossing. Based on this theory and method, researchers have developed elite germplasm of the new plant type such as Shennong 89366 and super high-yielding japonica varieties (Shennong 265 and Shennong 606) with large, erect panicles. In terms of photosynthetic efficiency and biomass production, an erect panicle type could be another phenomenal change in adjusting the japonica rice plant type to achieve maximum yield, following breeding for dwarfness and the ideal plant type. Increasing yield in irrigated boro rice through indica/japonica improved lines in West Bengal, India S.K. Bardhan Roy Boro (dry season) rice has made a significant contribution to the growth in rice production of West Bengal. Its main contribution has come from growth in area, whereas the growth rate of productivity has remained only 2.9%. However, the growing environment of boro rice provides an opportunity to reach a yield of 13 t ha-1 with a suitable plant type. Several indica/japonica (I/J) lines were screened and evaluated for high grain yield in the boro season. The highest grain yield of 9.2 t ha-1 was obtained from selected I/J line IR58565-2B-12-2-2, which was equal to that of indica hybrid CNHR3 and significantly higher than that of modern variety IR36. Panicle length and spikelet number were higher in selected I/J lines. On-farm tests revealed a 21% higher grain yield with superior grain type. Selected I/J lines are suitable for increasing the productivity of boro rice in West Bengal. Breeding rice varieties for higher productivity in the Mekong Delta of Vietnam Bui Ba Bong The Mekong Delta (Cuu Long), with a rice area of 4.0 million ha, produced half of the total rice production in Vietnam and supplied 4.5 million tons of milled rice for export in 1999. Sixty percent of the rice area is irrigated with intensive cultivation of two to three crops per year. The average yields of improved varieties are now 6 t ha-1 in the dry season and 4 t ha-1 in the wet season. During the past ten years, yield increased 1 t ha-1 or 2.4% per year. To sustain this increased rate, we have focused on breeding rice varieties for high yield potential, resistance to brown planthopper and blast disease, and good grain quality. The target is to increase the average yield from 6 to 7 t ha-1 in the dry season and from 4 to 5 t ha-1 in the wet season. What governs ceiling yield and its rate of attainment? J.E. Sheehy, P.L. Mitchell, J. Dionora, and A. Ferrer The goal in an ideal agricultural system would be to achieve the greatest possible yield in the shortest possible time using minimum inputs. There are perhaps an unusually large number of uncertainties in the area of research concerned with breeding for higher yield and they give rise to a number of important questions. What is the maximum yield achievable in a given growing period? What are the uncertainties surrounding estimates of yield limits? Can we construct rice ideotypes that are useful in the pursuit of ceiling yields? Are yield and quality inversely related? Does the concept of hybrid vigor become invalid as yield limits are approached? What is the likely role of genetic engineering in the pursuit of higher yields? The above questions are addressed in this paper. P.L. Mitchell, J.E. Sheehy, and F.I. Woodward Given the need to increase rice yields substantially, a rice plant with C4 photosynthesis produced by genetic engineering could be of value. We analyzed the losses of potential fixed carbon when scaling up from theoretical quantum yield to grain yield to identify the differences between rice and maize. Maize has a higher measured quantum yield since photorespiration is suppressed and canopy photosynthesis is increased by higher maximum rates of leaf photosynthesis arising from the higher concentration of carbon dioxide around Rubisco. A successful C4 rice plant must possess both these features, which are associated with the combination of the C4 biochemical pathway and specialized (Kranz) anatomy. In addition, improvements in primary partitioning (from initial products of photosynthesis to sucrose, starch, and amino acids) are probably necessary to fully exploit higher rates of photosynthesis. Tillering duration and yielding ability of rice varieties in the winter rice season of Bangladesh A.R. Gomosta, H.A. Quayyum, and A.A. Mahbub In Bangladesh, the winter rice crop (boro) is an irrigated crop. Among the three rice seasons of Bangladesh, it is the longest rice season, producing the highest grain yield. The winter season crop begins in November and ends in May. Farmers sow their seeds, however, between November and February. The tillering duration of the crop varies because of different sowing dates or transplanting dates in the winter season. The different duration of tillering has a positive association with the duration of low temperature (below 20 ºC), at which the vegetative phase of the crop is exposed. A longer crop duration allowed the tillers to become more mature, producing a higher number of panicles in the winter season. In the winter-season crop, the use of different-aged seedlings and time of seeding was more flexible for long-duration varieties than for short-duration varieties. A short-duration variety such as BR28 could produce 6 t of grain yield when 30-d-old seedlings from a November-seeded bed were used. Seedlings from an October-seeded bed produced only 1-2 t of grain yield. However, 30-90-d-old seedlings of BR29, a long-duration variety, produced 5-7 t of grain yield when seedlings from an October-seeded bed were used. M. Dingkuhn, F. Tivet, P. Siband, F. Asch, A. Audebert, and A. Sow Specific leaf area (SLA), defined as the ratio between leaf blade area and its dry weight, determines the physiological cost of producing leaf area. Theoretically, at a given pattern of assimilate partitioning among plant organs, varieties having high SLA should produce a leaf area more rapidly than those having low SLA, or thick leaves. This is because the reduction in leaf photosynthesis caused by high SLA is more than offset by the gain in light interception during exponential growth. The same reasoning would call for higher relative growth rates (RGR) during exponential growth for varieties having high SLA. According to studies in 1986-90 at the International Rice Research Institute, RGR is correlated with tillering. One can therefore argue that SLA is physiologically linked with tillering ability. Studies at the West Africa Rice Development Association in 1995-98 indicated a positive correlation across genotypes between SLA and tillering ability, leaf area index (LAI), and weed competitiveness. The study used diverse genotypes, including traditional and improved Oryza sativa indica (lowland-adapted) and japonica (upland) types, as well as O. glaberrima landraces and interspecific crosses. A subset of these materials showed that varietal differences in SLA were already expressed before the plant became autotrophic and were carried through to the flowering stage. Recent studies at the Centre de coopération internationale en recherche agronomique pour le développement disaggregated the components of leaf area development, such as tiller and leaf appearance rate and genealogy, as well as leaf extension rates and final dimensions for an O. sativa indica (high tillering, small leaves), an O. sativa japonica (low tillering, large leaves), and an O. glaberrima cultivar (high tillering, intermediate leaves). For all cultivars, a common linear relationship was observed between relative tillering rate (RTR) and RGR. This relationship was quite robust across development stages, except the reproductive stage, and across different levels of temperature and drought. Differential tillering rates and leaf area development among varieties and environments were therefore related to dry matter acquisition, based on a common relationship for morphologically and phenologically different materials. We conclude that there is a strong case for SLA being responsible to a large extent for varietal differences in tillering ability and LAI in rice. Varietal differences in tillering ability may in fact be due to inherent growth ability. High SLA (thin leaves) is a major factor enabling early ground cover and light interception; therefore, it determines potential growth in many situations. Once ground cover is complete, however, high SLA becomes disadvantageous because leaf photosynthetic rates then limit growth. Consequently, the most efficient plant type in terms of growth would have high SLA during early growth stages and low SLA for leaves produced later on. Such a plant type would have high and early tillering. This reasoning, if accurate, has far-reaching consequences for plant-type concepts and selection criteria because selection for low-tillering types would most likely favor low-SLA types, associated with poor vegetative growth vigor and weed competitiveness. The new plant type is discussed in the light of these results. Structure of rice caryopsis in relation to strategies for enhancing yield G.A.I. Ebenezer, S. Krishnan, and P. Dayanandan Rice varieties with higher yield potential can be developed by increasing the number of grains per area, by increasing the grain weight, or by a combination of both. Our studies on the structure, histochemistry, grain filling, and response to plant growth regulators (PGRs) have clarified certain unique features of the spikelet of rice grains and have identified strategies required to enhance the weight of rice grains. The most important barrier to grain weight is the space limitation imposed by the fertile glumes, the palea and lemma within which the caryopsis should develop. Experiments with intact plants and excised spikelets reveal that most PGRs, singly or in combination, do not influence the growth of glumes. Brassinoloide (BR) promotes growth of the palea and lemma when applied during the panicle initiation stage. BR at 10-7 M and benzylaminopurine (BAP) at 10-5 M applied together as a soaking spray increase grain size and dry weight by 39%. This is achieved through promotion of cell size and cell number, of both the palea and lemma, and the caryopsis within. The aleurone cells of the treated grains increase to 160,000 from 75,400 in control grains. Strategies for yield improvement could aim at increasing the dry grain weight, either by (1) breeding rice varieties with a larger palea and lemma or by (2) producing varieties that respond to PGR application by rapidly increasing the size of the palea and lemma. Erik H. Murchie, Stella Hubbart, Shaobing Peng, and Peter Horton Projected increases in rice grain yield are likely to require an increased rate of biomass production, which will demand a greater canopy photosynthetic assimilation rate (CAP). There is evidence that the radiation-conversion efficiency (RCF: the aboveground biomass produced per unit of radiation energy intercepted) for rice is lower than that of other C3 crops. One of the components of CAP is the leaf-level photosynthetic rate (P). We have investigated variation in light-saturated photosynthetic rates (Pmax) of rice plants in the field. We compared IR72 and the new plant type (NPT) and examined responses to (1) leaf age during grain filling and (2) position within the rice canopy. Photosynthesis during grain filling accounts for between 60% and 100% of the carbon in mature rice grain: following flowering, Pmax in the flag leaf either declined gradually (IR72) or was generally sustained for the greater part of the grain-filling period (NPT). In both cases, it was difficult to link changes in photosynthesis to the decline in Rubisco content. In fact, a rise in Rubisco content was noted after flowering, which did not correspond to a change in Pmax. Pmax declined according to leaf position within the canopy; this was linked to available light at each position and also occurred alongside a reduction in Rubisco content. However, Pmax of the NPT was considerably lower than that of IR72. An improved RCF could occur by raising leaf-level Pmax and by improving the photosynthetic responses of leaves lower in the canopy to high light. A coordination of biochemical and whole-plant studies will be needed. Qiao-quan Liu, Zong-yang Wang, Xiu-hua Chen, Xiu-lin Cai, Men-ming Hong, and Ming-hong Gu Rice (Oryza sativa) grain starch consists of amylose and amylopectin. The amylose content in the endosperm is a key determinant of rice eating and cooking quality. High amylose levels are usually associated with dry, fluffy, and separate cooked rice. The waxy (Wx) gene is known to encode the granule-bound starch synthase responsible for the synthesis of amylose in the rice endosperm. To improve rice cooking quality, several elite rice cultivars were selected for transformation with the antisense Wx gene using the Agrobacterium-mediated method. A chimeric antisense gene containing the 3.1-kb portion of the 5¢ upstream region from the translational starting site of the rice Wx gene, a 0.75-kb antisense waxy DNA fragment, the gus reporter gene, and the nos terminator were constructed and inserted in the T-DNA of the binary vector pCAMBIA1300. The resultant Ti-plasmid, p13W4, was used to transform calli derived from immature embryos 12-15 d after pollination via Agrobacterium tumefaciens. More than 1,000 transgenic plants have been regenerated from several elite cultivars including japonica and indica. The analyses of polymerase chain reaction (PCR) and Southern blot hybridization confirmed that the T-DNA containing the antisense construct has been integrated into the genome of the transgenic rice plants. Data from GUS activity showed that the GUS fusion gene could express efficiently in the endosperm, but was less detected in the leaves, stems, and roots of the transgenic rice plants. In some of the seeds from these transformants, a range of reduction in the apparent amylose content was found (up to a maximum of nearly 100% reduction). A reduction in the kernel weight of some transgenic plants was also detected (up to a maximum of 7-8% reduction in several transgenic plants, whereas the amylose content dropped below 1%). Genetic analysis suggested that the foreign gene and amylose content in these transgenic plants could be transmitted stably. Now, a lot of elite transgenic lines (T5-T7 generation) with lower amylose have been selected for a continuous test. Exploitation and Use of Heterosis in Rice Breeding of super hybrid rice Yuan Longping Plant breeders realize that there are only two effective ways to increase the yield potential of crops through breeding: improving morphological traits and using heterosis. However, the potential is limited when improving morphological traits alone and heterosis breeding will produce undesirable results if it is not combined with improved plant morphology. Any other breeding approaches and methods, such as molecular breeding, must be incorporated along with good morphological characters and strong heterosis, otherwise there will be no real contribution to increasing yield. On the other hand, further developing plant breeding for high targets must rely on the progress of biotechnology. Opportunities and challenges of developing and using hybrid rice technology in the tropics S.S. Virmani By 2025, we anticipate a 40% increase in global demand for rice. Therefore, we need to produce more rice per unit area per unit time. The success of hybrid rice in China has encouraged IRRI and several tropical countries to explore the prospects of this technology to increase their rice yields. Although Chinese rice hybrids and parental lines were not usable as such in the tropics, the presence of significant heterosis in tropical rice was amply demonstrated. IRRI scientists developed several cytoplasmic male sterile, maintainer, and restorer lines and heterotic combinations and shared these with NARS. Some of these have been released for commercial cultivation as such and others with some local modifications. Farmers have also reported a yield advantage of at least 1 t ha-1 from some of the released hybrids. Concurrently, hybrid rice seed production technology was also developed for the tropics, which allowed seed yields of 0.5-3 t ha-1. Hybrid rice is now being grown commercially in India, the Philippines, and Vietnam, and several other countries are exploring the prospects of its commercialization. These developments have encouraged private seed industries (both national and multinational) to invest in hybrid rice technology generation and/or seed production and marketing. IRRI and national agricultural research systems (NARS) have been collaborating to harness human resources to develop and use the technology. Major challenges to the large-scale adoption of hybrid rice technology in the tropics are very high expectations of farmers, inconsistent performance of the first set of released hybrids, inadequate understanding of agronomic management of hybrids, inadequate availability of pure seeds of parental lines and hybrids, poor grain quality of hybrids in comparison with premier-quality rice, inadequate level of disease/insect resistance in the released hybrids, inconsistent seed yields, high cost of hybrid seeds, and the habit of rice farmers to use their own seed. Inadequate linkage and understanding between research and seed production agencies and inadequate coordination among research, seed production, and technology transfer agencies also constrain the large-scale adoption of the technology. Future opportunities exist for enhancing the level of heterosis through indica/tropical japonica hybrids and the selective use of heterotic groups and gene blocks; developing better agronomic, nutrient, and pest management practices; improving grain quality and disease/insect resistance of hybrids; developing hybrids for stress-prone environments; and direct seeding. Prospects of further increasing seed yields and reducing input costs in hybrid seed production plots are also real. Work is in progress in all these areas. Besides developing better rice hybrids, the transfer of this technology can also be facilitated by establishing effective mechanisms to link research and seed production and technology transfer systems. To strengthen these systems, IRRI collaborates with seven NARS, the Food and Agriculture Organization (FAO), and Asia Pacific Seed Association (APSA) in an ADB-funded project "Development and Use of Hybrid Rice in Asia." Hybrid rice technology in China helped to increase its global rice production by about 20 million t per annum. This spares an estimated 6 million ha of land every year from rice production. Any additional area under this technology would further contribute to global food security and environmental protection. Hybrid rice in Bangladesh: opportunities and challenges A.W. Julfiquar, S.S. Virmani, M. Mahiul Haque, M.A. Mazid, and M. Mostafa Kamal Hybrid rice is one option for increasing the yield ceiling in rice by 15-20% over the best modern varieties. The development of hybrid rice technology in Bangladesh began in 1993. Initial work on hybrid rice involved testing F1 hybrids and evaluating cytoplasmic male sterile (CMS) and restorer lines received from IRRI. The CMS lines IR58025A and IR62829A were adaptable and stable with an outcrossing rate as high as 33.8% and 41.0%, respectively. Some well-adapted varieties/lines were identified as maintainers or good restorers for the wild abortive cytosterility system. Some elite maintainer lines identified are BR29, BR5876-6-2-1, BR4839-17-2-2-HR42, BR5690-62-23, BR5882-12-2-1, and BR5892-32-5-3. Some CMS lines and their maintainers from China were also evaluated for their adaptability and performance. However, these lines were not adapted to Bangladesh conditions and were highly susceptible to disease and insects. Several IRRI-developed hybrids, tested in multilocation yield trials during the 1995-96 boro season at Gazipur, Comilla, Bhanga, and Habiganj, outyielded the standard check variety of the same duration by more than 1 t ha-1. Grain quality characteristics of the tested hybrids were comparable with those of our recommended check varieties. Two hybrids, IR69690H and IR68877H, are being tested in the National Hybrid Rice Trial during the boro season 1999-2000 for possible recommendation by the National Seed Board. IR69690H has growth duration similar to that of BRRI Dhan 29 and IR68877H has growth duration comparable with that of BRRI Dhan 28. These two hybrids have shown about a 1 t ha-1 yield advantage over the check variety of similar duration in multilocation trials and on-station trials in different regions of Bangladesh. Trials conducted on seed production during the past two years have shown that six rows of a CMS line and two rows of a maintainer line appeared to be the optimum row ratio for obtaining the highest seed yield for CMS multiplication. For hybrid seed production, eight rows of a CMS line and two rows of a restorer line seem to be the optimum row ratio. Hybrid seed yield increased significantly over seasons from 24 kg ha-1 to 1.08 t ha-1. F1 seed yield was higher during the boro season than in the T. aman season. Recent developments in hybrid rice research in India K. Krishnaiah, B.C. Viraktamath, M. Ilyas Ahmed, C.H.M. Vijayakumar, and M.S. Ramesha Rice occupies a pivotal place in India's food security and livelihood system. The country has to produce about 135-140 million tons of rice by 2020 to meet its ever-increasing food requirements. Recognizing the potential of hybrid rice to enhance production and productivity, a goal-oriented project on hybrid rice was launched by the Indian Council of Agricultural Research (ICAR) in 1989. Since then, significant progress has been made in developing hybrid rice. More than 1,000 experimental hybrids were evaluated and 13 hybrids (12 from the public sector and one from the private sector) have been released for commercial cultivation. Many cytoplasmic male sterile (CMS) lines and restorers were evaluated and promising lines have been identified. These lines are now being used to develop new hybrids. Experimental hybrids were screened for quality and resistance to major pests and diseases and promising hybrids were identified. Major efforts have been made for efficient and economic seed production. A series of trials were conducted to determine optimum row ratio, planting pattern, GA3 requirement, supplementary pollination techniques, etc. A seed production package has been developed based on these results. Seed yields that were <100 kg ha-1 during the initial stages have risen to 1.0-1.5 t ha-1 because of the advent of this package. Specific breeding programs were begun to improve parental lines. New approaches such as the development of iso-cytoplasmic restorers, cross breeding of restorers and maintainers, and population improvement by using male sterility-facilitated recurrent selection have helped to isolate 1,400-1,500 derivatives that will be useful in hybrid rice breeding. To enhance the levels of heterosis, two-line breeding and indica/tropical japonica hybridization methods are being deployed. More than 50 thermosensitive genetic male sterile lines were screened and five lines have been identified as promising based on their distinct transformation behavior and other desirable agronomic features. Fifty experimental two-line hybrids were evaluated and promising combinations were selected for further testing. To develop indica/tropical japonica hybrids, promising tropical japonica lines were screened and those possessing wide compatibility (WC) genes have been identified. Emphasis is being given to improving grain quality and incorporating resistance to major pests and diseases. Exploiting rice heterosis in the Philippines Edilberto D. Redoña, Frisco M. Malabanan, Leo J. Javier, Salvador I. Yabes, Samuel A. Ordoñez, and Santiago R. Obien The use of hybrid rice technology as a major approach for further increasing rice production has been recognized in the Philippines with the inclusion of hybrid rice technology as an integral component of the Department of Agriculture's rice production program in January 1998. Using three released hybrids, PSBRc26H, PSBRc72H, and PSBRc76H, large-scale seed production and technology demonstration activities began in the 1998 dry season. National capacity for hybrid rice development and use is continuously being strengthened through training activities implemented nationwide, with more than 800 agricultural technicians, seed inspectors, local government officers, and potential seed growers participating in more than 20 training courses on hybrid rice seed production to date. Hybrid rice research and development, on the other hand, has been strengthened with the establishment of a multidisciplinary PhilRice Hybrid Rice Program, the conversion of the PhilRice branch station in Isabela into a hybrid rice center, and the forging of research collaboration with IRRI, five Chinese hybrid rice research institutions, and hybrid rice programs of other countries. The participation of the private sector is encouraged to expedite the development and farmer adoption of the technology in the country. Research and development of hybrid rice technology in Sri Lanka S.W. Abeysekera, D.S. de Z Abeysiriwardena, and M.P. Dhanapala Research and development for hybrid rice in Sri Lanka passed through three main stages: the evaluation of F1 hybrids for heterosis, the transfer of cytoplasmic male sterility (CMS) from adapted CMS lines to promising Sri Lankan rice varieties, and development of a locally adapted package of management practices for hybrid rice seed production. During the past four seasons, 26 IRRI-bred CMS lines were evaluated and their pollen sterility ranged from 87% to 100% and only the lines with 100% sterility were used. Of these, 25 were uniform and adaptable to local conditions. Outcrossing was very high in IR62829A, IR69625A, IR68899A, and IR58025A (26-40%). Out of the 156 heterotic combinations made using adaptable CMS lines, 11 combinations were promising. Out of 1,271 test crosses evaluated, 56 were highly sterile. These potential CMS lines are now in the BC2 and BC3 generations. Nine F1 hybrids developed at the Rice Research and Development Institute (RRDI) have been evaluated in yield trials at target locations during 1999. Some hybrids were promising with a yield advantage of more than 1 t ha-1 over inbred checks. Ten IRRI-bred rice hybrids were tested in an international coordinated hybrid rice yield trial during the 1999 major (wet) season at two target locations. Three F1 hybrids (IR71092H, IR67693H, and IR64616H) outyielded the local and international checks by 26-33%. Leaf CO2 assimilation of IR71627H was higher than that of Bg357 (the highest-yielding inbred variety in Sri Lanka). The yield of IR71627H was always greater than that of Bg357 by 20-30% at all levels of fertilizer tested. Seed of some of the promising F1 hybrids was produced by the isolation-free method and strict-isolation method. With these methods, 0.75-1 t ha-1 seed yield was obtained for each combination. The commercialization and performance of hybrid rice in the United States Robin D. Andrews The development of hybrid rice for the mechanized farming system used in the United States began in 1980, in the private sector, with a contractual arrangement between the China National Seed Corporation and a U.S. company. Subsequent attempts to grow hybrid rice in the U.S. on a farm scale were unsuccessful. In the early 1990s, the partly developed knowhow and germplasm were acquired by RiceTec AG (Vaduz, Liechtenstein), which invested heavily in solving the economic and quality problems involved in meeting U.S. farmer, processor, and consumer requirements. RiceTec's germplasm development program and technical work were supported by a collaborative agreement with the Hunan Hybrid Rice Research Center in Changsha, Hunan Province, China. The development effort has been successful. In December 1999, RiceTec, Inc. (Alvin, Texas, USA) began selling the first hybrid seed in the U.S. Hybrid seed for approximately 6,000 ha is available for sale for planting in 2000 in the states of Arkansas and Missouri, located at approximately 36ºN. The price of hybrid seed on a per hectare basis is about three times that of varietal seed. In this chapter, we discuss the performance of this first commercial U.S. hybrid-denoted as XL6-relative to U.S. varieties in terms of yield, quality, and grower economics. XL6 is a conventional U.S. long grain in terms of grain dimensions and starch properties with a grain quality well suited to parboiling. In 1999, XL6 exhibited more than a 30% yield advantage over local varieties in large-scale field trials in Arkansas. The production of hybrid grain requires a change in cultivation practices on the part of the U.S. rice farmer, primarily related to substantially lower seeding rates and lower fertilization requirements. We describe the manner in which the added value of the hybrid is shared between RiceTec and farmers. Improving seed production to speed up the global commercialization of hybrid rice Changxiang Mao Hybrid rice in China and other countries has yielded 20-30% higher than the best inbred varieties. This yield advantage can contribute considerably to national and international efforts to achieve food security and alleviate poverty. In recent years, the hybrid rice-growing area in China has become more than 50% of the total rice area. Its commercial cultivation in developing countries outside China has expanded rapidly also, especially in Vietnam and India. Many stable cytoplasmic male sterile (CMS) lines and restorer lines have been developed by scientists from China, the International Rice Research Institute, India, Vietnam, and other countries. By using CMS lines with good general combining ability and specific combining ability (including environmental genetic male sterile lines) and R lines, more and more rice hybrids have been released and commercialized not only by breeding institutes but also by the seed sector. Breeding heterotic rice hybrids has thus become easier. But the major barrier to the further expansion of hybrid rice in many developing countries is its high price and poor quality of seeds. Chinese experience showed that, with efforts to improve seed production techniques, the nationwide average yield of hybrid seed in China increased from 0.27 t ha-1 in 1976 to 2.72 t ha-1 in 1997, with a record of 7.39 t ha-1. The cost of producing F1 seed has decreased from US$6 to $0.80 kg-1 during the same period and seed quality has also improved markedly. The refinement of seed production techniques, common efforts from the public and private sector and national and international seed sectors, and policy support from the government are solutions for further improving hybrid rice seed production, increasing its yield, and decreasing the cost of F1 hybrid rice seed in the 21st century. Adoption of hybrid rice technology in India: an economic assessment of early farm-level experiences A. Janaiah and Mahabub Hossain Policymakers and research managers in India considered hybrid rice, an innovative technology in the late 1980s, as an option for raising the yield frontier under irrigated environments. However, concerns are being raised about its acceptability on the part of hybrid rice farmers in view of its slow adoption in the target environments. This chapter aims to discuss this issue based on empirical evidence obtained from sample farmers, seed growers, traders, and millers of hybrid rice in irrigated rice systems in India during the 1997-98 crop year. On average, the yield gain of hybrid rice over that of popular inbred varieties was 16%. Under current pricing, hybrid seed production for rice is highly profitable. But hybrid rice grain brought an 11% lower price in the market than inbred varieties because of sluggish consumer demand, largely on account of inferior grain quality and lower head rice recovery. Therefore, the net return to hybrid rice production was 5% lower than that of inbred rice. Higher seed cost and lower output price brought about the lower profitability of hybrid rice production. To further develop hybrid rice, breeding for value addition through quality improvement, risk reduction, and increased heterosis was identified as a research priority. Breeding for Abiotic Stress Tolerance
Plant breeding for stress environments: Are we making progress? A. Blum Although conventional breeding has been attaining slow but steady progress in plant breeding for stress environments, an impressive effort is now being made to apply molecular biology as a means for accelerating progress. In this respect, molecular biology is applied via two main channels: (1) marker-assisted selection of physiological and developmental stress-resistance traits to augment conventional yield-based selection programs, and (2) genetic engineering consisting mainly of "mining" and "inserting" stress-responsive/adaptive genes that are expected to transform plants into being more stress resistant in the field. The first channel appears to have produced an increasing number of successful cases in recent years. It is presently limited mainly by the often poor quality of phenotyping of the mapping populations for stress-resistance quantitative trait loci. It might be limited in the future by the presently insufficient research in crop stress physiology. The genetic engineering approach is still wrestling with problems of concept and procedure. Advanced technologies are turning the identification and cataloguing of stress-responsive genes into a routine. The dilemma is mainly in identifying and quantifying the function and value of the candidate gene-in the whole plant and under the relevant stress scenario in the field. The difficulties stem from known problems of gene expression in the transgenic plant, which are exacerbated by unnecessary faults in testing plants for stress resistance. An examination of the main components of the problem leads to the conclusion that genetic engineering for improved crop stress resistance carries a proven potential, but the realization of this potential in the field requires close collaboration between the molecular and physiological/agronomic disciplines. Progress being made in the application of marker-assisted selection to plant breeding for stress environments is a successful case of such collaboration. Development of rice yield components in irrigated upland and lowland environments H.R. Lafitte and B. Courtois As water for agriculture becomes scarcer, some lowland areas will be forced to shift to upland rice cultivation. Rice generally yields less in aerobic systems. To obtain adequate yields, we need to understand the causes of reduced productivity in upland conditions and their genetic control. This chapter combines results from variety comparisons, a doubled-haploid line (DHL) mapping population, and near-isogenic lines (NILs) to address these questions. The development of leaf area index was greater in aerobic conditions for an upland variety, Azucena, and also a lowland variety, IR72. For both varieties, the percentage of sterile grain was greater and the 1,000-grain weight less in aerobic conditions, leading to a lower harvest index in the upland field. The reduction in harvest index was more severe in the lowland cultivar. We also compared yield components measured in sprinkler-irrigated upland, furrow-irrigated upland, and lowland conditions for 85 DHLs derived from a cross between another semidwarf indica lowland cultivar, IR64, and Azucena. Yields and most yield components were poorly correlated across upland and lowland environments. Common quantitative trait loci (QTLs) were identified across water levels for some traits, but QTLs for yield and yield components were generally specific to one environment. Additional studies examined the performance of NILs of IR64 that had chromosomal segments from Azucena introgressed through marker-aided selection. The introgressed segments were chosen because they contained QTLs for root traits (e.g., root thickness, length), but some yield component QTLs had also been mapped near those segments. When the NILs were cultivated under lowland conditions, they produced fewer tillers per plant than did IR64, but some produced more tillers m-2 in the uplands. Preliminary yield data indicate that some NILs can outyield IR64 in lowland and/or upland conditions. These results provide insights into the genetic control of the development of rice yield components in aerobic and anaerobic environments. Combining ability analysis for physico-biochemical traits influencing drought tolerance in rice H.D. Mohan Kumar, P.M. Salimath, S.A. Patil, M.B. Chetti, V.V. Shenoy, and H.M. Vamadevaiah Combining ability analysis was carried out in rice through line × tester analysis for physico-biochemical traits influencing drought tolerance such as relative water content (RWC), proline accumulation (PRO), and epicuticular wax (EW) content at the 95th day (S1 stage) and 105th day (S2 stage) under a moisture stress-free environment (E1) and moisture stress at the reproductive stage (E2). The inheritance of these characters in both environments (E1 and E2) and at both stages (S1 and S2) was primarily under the control of additive gene action. The ratio of variances due to general combining ability and specific combining ability (s 2 GCA/s 2 SCA) was more than 1, indicating the preponderance of additive genes in controlling these characters. The genotypes Rasi, MTU-1001, and Annada for RWC, Rasi, Amruth, and Sona Mahsuri for proline accumulation, and Bilekalavi, Kempukalavi, and Amruth for epicuticular wax content emerged as the best general combiners. Under the stress condition (E2), four hybrids each for RWC and PRO and 22 hybrids for EW content expressed significant positive SCA effects. The superior cross combinations were obtained from high × high and high × low general combiners. In view of the preponderance of additive genetic components in controlling these characters, it is expected that their genetic advance through single-plant selection would be quite rewarding. S. Pandey, D. Behura, R. Villano, and D. Naik Drought is one of the major production constraints to rice production in eastern India, which has almost half of the country's total rice area. Severe droughts in this poverty-stricken region adversely affect the livelihoods of millions of people. In addition to losses in rice production during the rainy season, food grain production during the postrainy season can also be severely affected. The second-round effects of drought are losses in employment in farm and rural nonfarm industries, losses in livestock production because of poor health and mortality, loss of land, migration, hunger, and social deprivation. The impact is highest among the most vulnerable groups of people who, even during normal times, are among the poorest. Even though drought may not be of intensity severe enough to result in famine, many poor people suffer economically and socially because of their inadequate access to institutional mechanisms that help smooth consumption over time. This chapter analyzes the economic cost of drought in eastern India. The value of rice and nonrice output lost in drought years was calculated based on an analysis of state-level data for the period 1970-96. The total value of output lost averaged over the 27-year period was estimated to be as high as $400 million per year. This is certainly a substantial cost, accounting for about 8% of the total value of agricultural production. Using panel data of farm households, we analyzed various strategies that farmers have adopted to reduce the loss from drought. Changes in cropping patterns, reduction in rice area, and changes in rice varieties and input usage were the major strategies employed when drought was of milder intensity and occurred during the early part of the growing season. During severe droughts when crops failed completely, a range of consumption-smoothing strategies such as local nonfarm income, sale of assets, borrowing, and migration were used. A substantial proportion of households suffered a major reduction in consumption despite these strategies. Vulnerable groups such as women and children suffered the most. The effect of drought was not limited to the year when drought occurred but it lingered on for several years as farmers attempted to rebuild the stock of productive farm assets such as livestock depleted during drought. These economic effects are quantified based on farm data from eastern Uttar Pradesh and Orissa. During severe droughts, informal arrangements based on mutual help were inadequate to prevent a drop in consumption of the poor. As inability of the poor to gain access to formal sources of credit and other types of formal mechanisms to smooth consumption is a major reason for the persistence of poverty in these drought-prone environments, a range of technological and policy interventions that are needed to improve risk-coping mechanisms are suggested. Recent advances and future strategies for breeding salt-tolerant rice varieties B. Mishra, R.K. Singh, and D. Senadhira Major breakthroughs have been achieved in breeding of high-yielding salt-tolerant rice varieties for various inland saline, coastal saline, and alkaline soils of fragile ecosystems. Out of 32 salt-tolerant rice varieties developed by the Central Soil Salinity Research Institute (CSSRI), the first dwarf high-yielding salt-tolerant early maturing rice varieties, CSR10 and CSR11, are popular as biological amendments for resource-poor farmers and are being used as low-cost technology for salt-affected soils. Fine-grain salt-tolerant rice varieties CSR13 and CSR27 were also developed. CSR13 (CSR1/Bas 370//CSR5) is adapted to alkaline (pH 9.2-10.0) and inland saline (up to EC 9 dSm-1)-stressed soils and resistant to major pests and diseases. CSR27 (Nona Bokra/IR5657-33-2) possessing dual tolerance for coastal salinity (up to EC 10 dS m-1) and sodicity (pH 9.2-9.9) and resistance to major pests and diseases was released across the country in 1999. Variety CSR27 possesses high tissue tolerance and high tolerance for K+ and phosphorus deficiency. We have developed basmati qualities along with salt tolerance in CSR30. It takes 113-116 d to flower and is recommended for partially reclaimed sodic soils of Uttar Pradesh and Haryana. It has yielded more than Taraori Basmati in normal soils with the same quality parameters and has better resistance to diseases and pests. The F1 anther culture-derived varieties CSR21 and CSR28, along with rice varieties CSR11, CSR18, CSR23, CSR24, CSR26, CSR29, and CSR30 having wider adaptability, are in the pipeline for release. CSSRI-IRRI partnership efforts through shuttle breeding have been successful and more than a dozen rice varieties have been developed for various problem soils. A wide spectrum of rice germplasm has been evaluated and categorized based on tissue tolerance, Na+ exclusion, K+ and P uptake, and reproductive-stage tolerance. Results showed that no single mechanism was responsible for absolute salt tolerance. We have been able to combine different physiological mechanisms into one genetic background. The advanced progenies have more than two mechanisms of increased tolerance for P, K, and Zn deficiency. There was no correlation of vegetative-stage salinity score with reproductive-stage salinity score and grain yield. K+ content exhibited a strong positive correlation with grain yield and the ratio of Na-K revealed significant negative correlation with grain yield. Genetic components of salinity tolerance, K+, and Na-K ratio were investigated. The significant specific combining ability effect for salinity tolerance can be exploited by hybrid rice breeding. Identifying rice lines for improved salt tolerance from a mapping population Raziuddin Ansari, Aisha Shereen, T.J. Flowers, and A.R. Yeo Rice lines subjected to 50 mM NaCl (corresponding to EC of 6 dS m-1) generally showed an adverse effect of salts on plant height, total and productive tillers, days to flowering, leaf area, straw and grain weight, panicle length, and sterility. These characters exhibited large variations between lines. In the F9 generation, phenotype stability is evident within individual lines. Calculated as percent reduction in grain weight compared with the respective controls, there was no adverse effect of salinity on 20 lines, 30 lines suffered less than 30% reduction, 30-50% reduction was observed in 50 lines, and the rest were more sensitive. Keeping high-yielding but salt-sensitive local cultivar Khushboo 95 as a check, ten promising lines have been selected that show satisfactory yield under the control and suffer less than 50% reduction at 50 mM NaCl salinity. Sanjay Singh, O.N. Singh, R.K. Singh, and S. Sarkarung Efficiencies of modified bulk (MB) and single panicle selection (SPS) were compared following selection in the F3 to F6 generations of five rice crosses. In both cases, 21-d-old seedlings of the F3 generation were submerged for 7 d and selection was made from the surviving plants. The later generations were grown in natural flood-prone conditions. In all, 100 single panicles were selected in F3. For SPS, the seeds of each of 100 panicles were collected separately and sown using the panicle-progeny-row method. Again in F4, one panicle each from the best 100 plants was selected and seeds from each panicle were collected separately for the next cycle of selection. The process continued until the F6 generation. For MB, five seeds from each of the 100 individual panicles were bulked to be space-planted in F4 and bulks continued until the F6 generation. From both SPS and MB populations, 20 progenies were selected in F6 and planted in F7 in a compact family block design in two replications with four checks, and observations were recorded on yield and other traits. Analysis of variance showed significant variances due to crosses and selected progenies within crosses for the SPS population for all the traits. MB progenies, however, showed no significant differences due to crosses and crosses versus selection. The SPS progenies had significantly higher yields than the MB progenies. Similarly, the number of lines superior to the best check was much larger for the SPS progenies than for the MB group. The SPS progenies also showed higher genotypic variance, heritability, and expected genetic advance. Factors influencing rice seedling vigor under different temperature treatments R.F. Reinke Rice cultivars with increased seedling vigor have been shown to accumulate biomass more rapidly during the vegetative stage under New South Wales (NSW) conditions. Rapid biomass accumulation is a necessary element in improving the productivity of short-season cultivars. The rice industry in NSW, Australia, requires cultivars with reduced growth duration. Such cultivars are essential for seasons in which the total amount of irrigation water allocated to farmers is reduced or when sowing is delayed. Given the association between seedling vigor and rapid biomass accumulation, this study investigated three variables influencing seedling vigor in 17 rice cultivars of diverse origins under three diurnal temperature regimes (8/22 ºC, 11/25 ºC, and 14/28 ºC), with the aim of assessing their relative importance and identifying traits that may be used to improve vigor. The variables were seed size, days from sowing to emergence, and leaf elongation rate (LER) immediately following emergence. Seedling vigor was measured as seedling biomass when the third leaf had fully expanded. The correlation coefficients between seedling biomass and each of the explanatory traits varied across the temperature treatments. Under the lowest temperature, LER had the highest correlation with biomass; at the intermediate temperature, the correlations between biomass and LER and between biomass and seed size were approximately equal; whereas, at the high temperature, emergence and seed size had the highest correlations with biomass. After accounting for correlations between explanatory traits, LER was still most closely associated with seedling biomass under both the low and intermediate temperature treatments, whereas, under the high-temperature treatment, the correlations of seed size and LER with seedling biomass were similar. Time to emergence had the lowest correlation with seedling biomass under all temperature treatments. These results indicate that seed size and LER both played significant roles in determining seedling vigor at the three-leaf stage. However, seed size is an important quality consideration for Australian rice, with increased seed size likely to prove unacceptable in many export markets. These results indicate that, under low temperatures, LER was more closely associated with seedling vigor than seed size, raising the prospect of indirect selection for seedling vigor on the basis of LER. The success of this approach rests on the genetic correlation of LER and seedling vigor, the narrow-sense heritability of LER, and the extent to which LER is associated with other traits such as plant height. Peng Xinxiang, Liu Yonghai, and Li Mingqi Oxidative stress during the ripening stage is considered to be a major cause of Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase) breakdown. This stress condition can be artificially created by treating plants with a well-known active oxygen inducer, methyl viologen (MV). In this experiment, MV was supplied through the roots of hydroponically grown rice seedlings (Oryza sativa L. cv. Shanyou 63). Under controlled conditions (29 ± 1 ° C and 135 m mol m-2 s-1 light intensity), Rubisco was lost at a rate of 1.2-1.4 mg g-1 fresh weight (FW) h-1 when 0.1 mmol L-1 of MV was applied. When some active oxygen scavengers were added to the oxidative treatment, the induced Rubisco breakdown was significantly inhibited. The degradation rate was decreased from 1.2 to 0.3 mg g-1 FW h-1 by ascorbate, from 1.2 to 0.6 by mannitol, and from 1.2 to 0.9 by benzoate. In addition, oxalate was effective in inducing resistance to oxidative stress. The degradation rate decreased from 1.3 to 0.8 mg g-1 FW h-1 when the plants were pretreated with 5 mmol L-1 for 2 d. The result further revealed that oxalate was able to induce the activities of some antioxidant enzymes. Pretreatment with oxalate doubled the activities of ascorbase peroxidase and superoxide dismutase, and increased catalase activity 25% compared with the control. This induction may be the mechanism for oxalate to induce resistance to oxidative stress. In conclusion, Rubisco breakdown, and photosynthesis as well, may be improved by exogenously applying some active oxygen scavengers or defense-response elicitors to the senescing leaves, or by selecting genotypes with a high level of endogenous antioxidants or antioxidant enzymes during the ripening stage. Using molecular markers to increase tolerance for phosphorus deficiency in rice (Oryza sativa L.) Matthias Wissuwa and Noriharu Ae Rice yields are frequently limited by soil deficiency for phosphorus (P). Increasing the P deficiency tolerance of rice cultivars may represent a more cost-effective solution to this problem than reliance on fertilizer application. Experimental evidence suggests that considerable genotypic variation for P uptake exists and that traditional varieties are likely to carry genes for high P uptake that have not been exploited in rice improvement. This chapter explores the possibility for transferring genes for high P uptake from the traditional variety Kasalath to a modern rice cultivar. The strategy followed here involves identifying molecular markers linked to genes for P uptake. The advantage of such markers in selecting genotypes with superior P uptake as well as in providing ideal plant material for physiological studies will be discussed. A population of 98 backcross inbred lines derived from a cross of the modern japonica cultivar Nipponbare with the indica landrace Kasalath was grown on a highly P-deficient volcanic ash soil (Andosol). Lines were genotyped at 245 restriction fragment length polymorphism (RFLP) marker loci and, by relating genotypic information to P uptake, four quantitative trait loci (QTL) for P uptake could be identified. One QTL linked to marker C443 on chromosome 12 had a major effect and lines carrying Kasalath alleles at this QTL had twice the P uptake as lines with Nipponbare alleles. Based on results of the QTL study, near-isogenic lines (NILs) for QTL C443 (chromosome 12) and QTL C498 (chromosome 6) were developed by three additional backcrosses to Nipponbare and subsequent selection for the desired RFLP markers. NILs genetically resembled Nipponbare to more than 90% but carried chromosomal segments from Kasalath at the respective QTLs. The effect of both QTLs could be confirmed using these NILs. P uptake of lines was not different with optimum P supply, but under P deficiency both NILs had significantly higher P uptake than Nipponbare. Genes at these QTLs therefore appear to encode for mechanisms specific to P deficiency. Initial physiological studies imply that Kasalath alleles at C443 and C498 enable lines to maintain relatively high rates of root growth under P deficiency, whereas root development is severely inhibited in Nipponbare. Genes at both QTLs can, however, not be considered general root size genes because the effect on root size can only be observed under P deficiency. The potential mechanism responsible for this effect will be discussed. These results show that genotypic variation for a quantitative trait such as P uptake can be attributed to several loci of known chromosomal location. Furthermore, it was demonstrated that it is possible to triple the P uptake of a modern rice cultivar by transferring these loci from a donor of low agronomic value. After fine mapping both QTLs, efforts will concentrate on cloning the underlying gene or genes. Once this has been accomplished, the transformation of modern cultivars promises to be far quicker than with traditional plant breeding methods. Durable Host-Plant Resistance
Durable host-plant resistance, a desirable trait for integrated disease management Anupam Varma and Neena Mitter The intensification of agriculture and introduction of new cropping systems have resulted in a change in disease scenario in various parts of the world. The emergence of new and damaging diseases has posed a major challenge to scientists for their eco-friendly management to achieve full potential of crop yield so that increasing demands for food and feed can be met in the 21st century. In the past, plant diseases have been managed effectively by host-plant resistance. Some of these resistances have been very stable, whereas pathogens overcome others in a short time. It is therefore desirable to have durable host-plant resistance to minimize losses caused by plant diseases. A resistance gene may have a durable effect for two reasons. First, a resistant variety may not be exposed to large amounts of inoculum, affording little opportunity for pathogen adaptation to overcome the resistance. Second, a genetic factor may prevent pathogen adaptation to a resistant variety despite a large population size. In different pathosystems, durable resistance could be controlled by single genes or multiple genes. Monogenic resistance could be based on a host component interfering with the pathogen or interaction of a host component with another host component or absence of a host component. Polygenic durable resistance is based on several host components that interfere with the pathogen. Genetically durable resistance in most cases is of a quantitative nature as reported for wheat3/4 P. graminis f. sp. tritici; maize3/4 P. sorghi; barley3/4 Erysiphe graminis f. sp. hordei; potato3/4 Phytophthora infestans; rice3/4 Magnaporthe grisea and Xanthomonas campestris pv. oryzae; and potato3/4 virus X and virus Y. Durability of resistance is a highly variable phenomenon. Recent developments in biotechnology have opened up new possibilities of incorporating durable resistance to pathogens in plants. For example, the introduction of both resistance and avirulence genes in plants could help in developing effective durable resistance in host plants. Transgenics for resistance to bacterial diseases are being produced. In viruses, genetically engineered resistance using coat protein, movement, and replicase genes is being exploited to produce resistant plants. Biotechnological approaches are also useful in marker-aided selection and RFLP mapping, identification of R genes, and gene pyramiding. Durability of the host against a pathogen cannot be predicted and can be seen only in retrospect. The strategy should be to manage resistance in such a way that the pathogen cannot overcome it. Recurrent selection of the host population against susceptibility and presumed major genes should be carried out. Pathologists and breeders should aim to achieve durable resistance in which the host plant is resistant in time and space. Insect-resistant transgenic aromatic rice expresses a barley chitinase gene and is resistant against sheath blight B. Ghareyazie, C. Menguito, L.G. Rubia, J. De Palma, A. Ona, T. Mew, S. Muthukrishnan, R. Velazhahan, G.S. Khush, and J. Bennett Enhanced levels of sheath blight resistance are reported in the advanced progenies of transgenic insect-resistant line Tarom Molaii containing a synthetic cryIA(b) and barley chitinase class II (CHI) gene. Microprojectile bombardment was used for transformation. Polymerase chain reaction (PCR) and Southern analysis showed the integration of the chitinase gene into the rice genome. The chitinase gene was inherited by the progeny of line #827. Immunoblot analyses of protein extracted from leaves of transgenic (PCR-positive) and control plants (PCR-negative) showed enhanced levels of CHI protein expression in this transgenic line. The eighth generation of line #827 was tested for resistance to sheath blight by artificial infection of plants with the causal fungus (Rhizoctonia solani). Resistance to the sheath blight pathogen was higher in the progeny of line #827 than in the nontransgenic control plants (Tarom Molaii). Transgenic basmati rice carrying genes for stem borer and bacterial leaf blight resistance S.S. Gosal, Raman Gill, A.S. Sindhu, Deepinder Kaur, Navraj Kaur, H.S. Dhaliwal, and Paul Christou Genetic engineering of basmati rice using synthetic cry1Ac and Xa21 genes has been achieved. Scutellar tissues of Pusa basmati 1, excised after 6-7 d from mature seeds, cultured on proliferation medium (MS + 2,4-D [2.5 mg L-1] + proline [560 mg L-1]), were bombarded using gold particles coated with a mixture of cry1Ac + Xa21 DNA on osmoticum medium (MS + 2,4-D [2.5 mg L-1] + mannitol [0.4M]). Bombarded tissues, after 2 d growth on proliferation medium, were subjected to hygromycin selection (30 mg L-1) for 2 cycles, 2 wk each. Plants regenerated on hygromycin (30 mg L-1) containing medium were screened using the histochemical GUS assay, polymerase chain reaction (PCR), and reverse transcript-PCR. Southern and western analysis of T0 and T1 plants confirmed the stable integration and expression of the cry1Ac. Transgenics included plants containing one or both of the two genes used for transformation. Segregation analysis during the T1 and T2 generations confirmed the Mendelian inheritance for marker, reporter, and cry1Ac genes. Insect bioassays during the T1 and T2 generations have shown enhanced resistance to yellow stem borer. Shaohong Zhang, Xiaoyuan Zhu, Bin Liu, Qiyun Yang, Lin Luo, Shangzhong Wu, and H. Leung Sanhuangzhan 2 (SHZ-2), an indica rice variety, has been widely planted in southern China for more than 10 years and has showed durable resistance to blast. The planted area for SHZ-2 and its derived resistant varieties has reached 660,000 ha. But there is a difference in disease resistance to blast among these derived varieties, and resistance in some of them has broken down in blast-conducive areas. In this research, seven pairs of primers designed from the conserved regions of cloned disease-resistance genes were used to analyze the differences among SHZ-2 and its derived varieties. These varieties could be clustered into different groups according to their DNA banding patterns. The clustering matched well with their disease reactions to blast pathogen isolates. Four varieties (SHZ-2, Waixuan 35, Sanluzhan 7, and Qingluzhan 11) with broad-spectrum resistance to blast were clustered into one group. The susceptible varieties are far from this group. Results indicated that resistance-gene analog genome scanning could reflect the difference in disease resistance to blast among these varieties. The short-lived resistance to blast for the derived varieties may be attributed to inadequate methods for identifying resistance genes in breeding. As a second component of this research, 250 recombinant inbred lines were developed using SHZ-2 (resistant) and Lijiangxintunheigu (susceptible japonica cultivar) to map the genes conferring durable resistance to blast in SHZ-2 using candidate defense genes. Backcrossing and marker-assisted selection were used to introgress the durable resistance from SHZ-2 into two popular indica cultivars in southern China: Texianzhan 13 (high-yielding, with good quality, but susceptible to blast) and Qisizhan (medium-yielding, with superior quality, but susceptible to blast). Two backcross populations (BC3F2) each with more than 100 lines have been obtained and molecular analysis and field tests for these lines are under way. Biotechnology for gall midge resistance: from molecular tagging to gene pyramiding Sanjay K. Katiyar and John Bennett Asian rice gall midge (Orseolia oryzae) is a major pest across much of South and Southeast Asia. This pest is genetically diverse and several gall midge biotypes are known to exist in each country. During the past three decades, host-plant resistance has proved to be the most effective mechanism for controlling the Asian rice gall midge. The appearance of different biotypes of this insect at different times and in different localities prompted the search for new resistance genes for use in breeding programs. Although several genes have been identified against Indian gall midge biotype I, there are still some biotypes for which either effective resistance genes have not been found or the resistance relies mainly on a single major gene. Some of the genes are rendered ineffective by the evolution of new gall midge biotypes. There is an urgent need to speed up the process of identifying, mapping, and using new genes and to maximize the durability of major gene resistance by gene pyramiding. DNA markers linked to resistance genes are useful for facilitating the introgression of one or more of these genes in breeding materials. Our efforts in the area of gene tagging, mapping and pyramiding resulted in the tagging of five gall midge resistance genes (Gm-2, gm-3, Gm-4, Gm-5, and Gm-6t) with several randomly amplified polymorphic DNA (RAPD) and sequence-tagged site (STS) markers and in the development of marker-aided selection kits. These kits are being used in China to transfer the Gm-6t gene to the parents of hybrid rice. DNA markers linked to these gall midge resistance genes facilitate the pyramiding of gall midge resistance genes to achieve durable and broader resistance against this pest. Induction and use of japonica rice mutant R917 with broad-spectrum resistance to blast Mingxian Zhang, Jianlong Xu, Rongting Luo, De Shi, and Zhikang Li R917, a japonica rice mutant with broad-spectrum resistance to blast, was selected by treatment of the F1 seeds from the cross between Chengte 232 and Xiushui 37 with 10 krad of 60Co g -ray. R917 was evaluated for blast resistance in multiple years and at multiple locations. It was resistant to 136 of the 138 isolates collected from different regions in China, with a resistance frequency of 98%, much higher than the 86% and 10% of Chengte 232 and Xiushui 37. To analyze its inheritance of resistance to blast, R917 was crossed with the susceptible cultivar Nonghu 6 and its two parents. It had a single dominant gene with resistance to races ZB13, ZC15, and ZE3, nonallelic to those of Chengte 232 and Xiushui 37. After being inoculated with seven Japanese differential strains, R917 showed the same reaction pattern as Toride 1 and differed from the other differential varieties, although R917 was different from Toride 1 in its reaction to seven Chinese races. The allelism test indicated that the resistance genes between R917 and Toride 1 were nonallelic to Chinese races ZC15 and ZE3. R917 was a semidwarf with a strong stem, narrow and erect leaf, tight plant type, and monogenic broad spectrum resistance to blast. Several lines newly bred using R917 as a donor of blast resistance had the same broad spectrum of resistance to blast as R917 and desirable agronomic traits, indicating that there is no linkage drag between the resistance gene and other important agronomic genes in R917. Recently, R917 has been used as a donor for many rice breeding programs in China. Blast infection and yield performance of blast-resistant multilines of rice Y.G. Kim, H.C. Choi, H.C. Hong, H.G. Hwang, S.N. Ahn, H.P. Moon, S.S. Han, and J.D. Ryu To ensure durable resistance to blast disease, we developed multilines of Chucheongbyeo and Suwon345. Field trials were performed over a 4-year period, 1996-99, at four locations in Korea. Two types of rice blast-suppressing effects of multilines were observed. Compared with the Chucheongbyeo multilines, the Suwon345 multilines showed a broader spectrum of race-specific resistance, but showed more severe neck blast infection and a lower suppression effect in both leaf and neck blast. These differences in suppressive effect on blast infection between multilines seemed to be due to the different field resistance between the two recurrent parents, suggesting the presence of different genetic components related to neck blast resistance. This study suggests that we should consider the genetic background of the recurrent parents when the multiline approach is used. Whitebacked planthopper resistance in Chinese japonica rice Kazushige Sogawa and Liu Guanjie Along with the widespread planting of hybrid rice in China in the 1980s, the whitebacked planthopper (WBPH) Sogatella furcifera has become a major pest of rice not only in hybrid rice area but also in japonica rice area in China and Japan because of its massive windborne migrations. We found a Chinese japonica rice, Chunjiang 06 (CJ-06), with a resistance mechanism against WBPH, by which WBPH eggs were quickly killed in the watery lesions induced at oviposition sites. In addition, CJ-06 expressed strong antixenosis and antibiosis resistance by suppressing WBPH sucking. These dual mechanisms of varietal resistance on CJ-06 may give it durable field resistance to WBPH. D.J. Pophaly, A.K. Gupta, D.K. Rana, and V.K. Verma The rice germplasm of the Indira Gandhi Agricultural University, Raipur (Madhya Pradesh), India, is a unique germplasm collection. This is the world's second largest collection of rice germplasm, which was collected from 1971 to 1988, but systematic studies for locating genes with resistance to various insect pests started only recently. From 1992 to 1998, about 7,500 rice accessions were evaluated against brown planthopper (BPH, Nilaparvata lugens) in the glasshouse where this insect is being mass-reared throughout the year on potted TN1 rice plants. So far, 327 rice accessions were identified with resistance to BPH on a 0-9 internationally accepted plant damage score scale (Entomology Annual Progress Report 1992 to 1998). However, 28 cultivars exhibited plant damage scores between 0 and 1. These are being considered as potential donors for genetic improvement programs. Other biological parameters, such as a feeding test on resistant cultivars and probing marks, clearly indicated that BPH behavior on these resistant cultivars differs, indicating variability in the genetic makeup of these resistant lines. Studies on wild rice for resistance showed that six lines of Oryza spontanea, O. nivara, and O. rufipogon were resistant to BPH. Studies on the genetics of BPH resistance indicated that the resistance is controlled by single dominant genes in cultivars OR1334-8, CRK7-2-8, TTB148-174-3-2-1, RP1579-1662-72-52, RP1976-18-6-4-2, RP1579-1627-32-220, and B6932-MR 25-1, whereas a single recessive gene was responsible in cultivars Basangi (B:2682), Bakada (B:2699), Barhi I (B:1253-I), Barhi II (B:1253-II), Lal Basant (L:289-I), and Budhiya Banko (B:57-II). In the cross combinations Lal Basant/Budhiya Banko, Lal Basant/Basangi, Barhi II/Budhiya Banko, Barhi I/Lal Basant, and Barhi II/Basangi, resistance was governed by two independent recessive genes. Duplicate dominant genes determine BPH resistance in the cross OR1334-8/TTB148-174-3-2-1. Identical alleles for BPH resistance were found in the crosses RP1579-1662-72-52/RP1976-18-6-4-2, B6932-MR25-1/CRK7-2-8, RP1579-1627-32-220/RP1976-18-6-4-2, and Bakada/Barhi I. Integrated Nutrient and Pest Management The quest for connections: developing a research agenda for integrated pest and nutrient management Gary C. Jahn, Peter G. Cox, Elsa Rubia-Sanchez, and Michael Cohen As we manipulate the rice ecosystem to improve production, the main components that we usually change are water availability, rice cultivars, and fertilizers. Biotic components of the rice ecosystem (i.e., microbes, flora, and fauna) change in response to these intentional alterations. Rice intensification, associated with increased fertilizer use, may increase pest problems. Conversely, some rice pest management tactics, such as burning rice stubble or adjusting water levels, could affect soil fertility and reduce the yields of certain cultivars. A deeper understanding of the interactions of varieties, nutrients, pests, yields, and production costs will allow us to integrate nutrient and pest management techniques for maximum benefit to rice producers and consumers. New cultivars (e.g., hybrid rice and low-tillering rice) and existing cultivars may interact with pests in different ways. If changes in cultivar and soil nutrient levels create new or more severe pest problems, then the effects of cultivar and fertilizers on natural enemies (of pests) must be considered as a possible cause of the changes in pest diversity. Results from greenhouse and field-plot experiments ultimately must be tested at the field and village levels. Depending on soil properties, water availability, and climate, it may be possible to put ecological theories into practice and manage some pest problems by adjusting soil nutrient levels. The challenge of understanding soil and cultivar interactions with pests and yield (SCIPY) can be approached from different directions. One research strategy, for example, would be to overlay maps of soil types, water availability, cultivar distribution, and pest distribution to characterize the ecosystems. Then, to use factorial combinations of fertilizer rates and cultivars in the different ecosystems to assess the effects on pest damage and yield. Another strategy would be to first identify cases where changes in cultivar and fertilizer interactions have specific effects on the biotic constraints to crops at a particular place and time. Then, to work back, to see how widespread the effect is, and to determine the underlying mechanisms. The advantage of this second approach is that it more rapidly leads to discoveries that can be applied to actual field problems through integrated nutrient and pest management. A third approach might not emphasize characterization or causation, but attempt to solve specific problems on a case-by-case basis through participatory means, that is, with farmers and scientists designing and conducting the research together. A fourth approach might combine deductive and inductive aspects with action research to simultaneously solve problems with farmers, build models, and investigate causation. This chapter describes the need to investigate SCIPY, the status of this research, and the advantages and disadvantages of various research approaches to this issue. Pest profiles at varying nutrient input levels P.C. Sta. Cruz, G.C. Simbahan, J.E. Hill, A. Dobermann, R.S. Zeigler, Pham Van Du, F.A. dela Peña, K. Samiayyan, Suparyono, Nguyen Van Tuat, and Zheng Zhong Pests were monitored over three seasons at six Irrigated Rice Research Consortium (IRRC) sites in China (Jinhua), India (Thanjavur), Indonesia (Sukamandi), the Philippines (Muñoz), and Vietnam (Cuu Long and Hanoi) to characterize pest damage profiles as affected by nutrient input levels based on the farmers' fertilizer practice (FFP) and site-specific (improved) nutrient management (SSNM). The research was superimposed on 137 monitoring farms of the Reversing Trends of Declining Productivity (RTDP) Project. Biophysical data were taken by the RTDP team and pest survey information was gathered by the pest impact assessment team at each site. For the first two monitoring seasons, sheath blight incidence was observed at all sites. Grain discoloration due to pathogens was recorded at five sites (except Jinhua) and was dominant at four sites (Cuu Long, Muñoz, Sukamandi, and Thanjavur). Red stripe was observed in Cuu Long and Sukamandi for both the dry and wet seasons. Other pests observed at each site were (1) brown spot, narrow brown spot, thrips, leaffolder, and rice bug in Cuu Long; (2) bacterial blight, brown spot, leaffolder, and stem borer in Hanoi; (3) stem borer in Jinhua; (4) kernel smut, narrow brown spot, rice bug, and whorl maggot in Muñoz; (5) narrow brown spot, stem rot, gall midge, stem borer, and rat in Sukamandi; and (6) bacterial blight, brown spot, gall midge, brown planthopper, leaffolder, stem borer, and whorl maggot in Thanjavur. Pest incidence in the FFP and SSNM usually differed. Damage-based assessments of sheath blight, grain discoloration, stem borer, leaffolder, and rat were higher in FFP than in SSNM plots. On the other hand, incidence of brown spot, red stripe, and whorl maggot did not significantly differ by nutrient management practice. Some pest- and site-specific cases showed the tendency to favor either the FFP or SSNM treatment; thus, further analysis of the data at specific sites is needed. Initially, the results showed that SSNM is effective in increasing yields from 5% to 20%, while pest incidence of five out of eight major pests observed was lower (compared with the farmers' fertilizer practice) in the improved nutrient management treatments at high pest incidence. However, this does not negate the possibility of differential trends at the site level. Effects of nitrogen, calcium, and silicon nutrients on bacterial blight resistance in rice Su-jein Chang, Dean Der-syh Tzeng, and Cheng-chang Li This study aims to investigate whether nutrient management can reduce epidemics of bacterial blight disease caused by Xanthomonas oryzae pv. oryzae in rice by determining the effects of nitrogen, calcium, and silicon on disease prevalence. Rice varieties with different levels of resistance to the disease were cultured under nutrient culture conditions. Different concentrations of nitrogen, calcium, and silicon were added to the nutrient solution to form different treatments. The X. oryzae pv. oryzae pathogen was artificially inoculated on the leaves of rice plants at the tillering and booting stages. When the disease appeared, the degree of disease infection was observed in terms of lesion length. The length of disease lesion on the leaves of resistant line TSWY7 increased with an increase in nitrogen levels, especially the plants grown under the high nitrogen level of 120 ppm pot-1. Under conditions of higher or lower level of calcium application, the disease lesion increased its length considerably at the tillering stage. The effectiveness of silicon in reducing bacterial blight disease epidemics was quite obvious in this experiment. This phenomenon was observed not only in the disease-resistant line TSWY7 but also in the susceptible variety TN1. A highly negative correlation (r = -0.998) was observed between silicon content (in leaves) and the length of disease lesions. A negative correlation was also observed between soluble sugar content in leaves and disease resistance. The results indicated that epidemics of bacterial blight can be reduced to some extent by applying silicon as a supplement to fertilizers. Recent advances in research on rice migrant insect pests in China Zhang Xiao-xi and Cheng Xia-nian The migratory characteristics and pathway of northward and southward (backward) migration of the rice pests brown planthopper (BPH) Nilaparvata lugens, whitebacked planthopper (WBPH) Sogatella furcifera, and rice leaffolder (RLF) Cnaphalocrocis medinalis were investigated in China from 1976 to 1982. The methods used were alpine net catch, aircraft and sea catches, mark-recapture, and dissection of ovaries. Physiological and ecological mechanisms of flight or migration, including oogenesis-flight syndrome, flight rhythm and energy resources, and the weather conditions that affect migration, were also studied during the 1980s. This chapter summarizes four aspects of recent advances during the 1990s, focusing on radar detection for migrants at high altitude and forecasting for rice migrant pests. Two types of radar, the X-band and Q-band, with centimeter and millimeter short wave, respectively, and an air net suspended from a "kytoon" (balloon) were used to detect migratory behavior during high-altitude flight of BPH and RLR. The "layering" and "non-orientation" behaviors and the aerial density and flight speed during autumn southward migration were described. Based on the parameterization of the migratory behavior detected by radar, trajectory analysis was used to explore the mid-scale emigratory sources of these two species, thereby substantially improving the accuracy of forecasting pest immigration. Various methods for long-, mid-, and short-term series forecasting for RLR and BPH were introduced. Indices for the long-term prediction of the relationship between the occurrence of an El Niño southern oscillation event and the outbreak of BPH in China were explored. Based on a geographic information systems platform, an attempt was made to establish a prewarning system for RLR and BPH. Wolfgang Reichardt, Ruthchelle de Jesus, Luu Hong Man, and Laddawan Kunnoot Observations of declining grain yields in intensive tropical rice cropping systems triggered a search for potential biochemical clues to soil N supply. Derived from a simplified "N pump model" describing the dynamics of biomass-linked labile soil organic N pools, the analytical targets comprised total soil protein including microbial biomass, soluble phenols, respiratory electron transport system (ETS) activity, and functional profiles of cultivable soil bacteria. Despite the absence of soil moisture fluctuation in a continuous intensive rice-cropping system, total soil protein concentrations reflected annual pool size changes of almost an order of magnitude. N-sink functions of total protein pools prevailed significantly in N-omission plots during the low-yielding wet season, whereas net immobilization was significant over all seasons. Intraseasonal variation of soil protein pool sizes was positively correlated with grain yields. The capacity of the soil to remineralize organically bound nutrients as indicated by electron transport system (ETS) activities was negatively correlated with soluble phenol concentrations. ETS activities as well as functional profiles of soil bacteria were altered due to interactive effects of nutrient and pest management. Representing biochemically defined soil constituents and processes, the parameters monitored are amenable to mechanistic models in soil biochemistry and, most importantly, can also be assessed at national agricultural research and extension systems using basic analytical laboratory equipment. Balanced nutrient management and beyond C. Witt, A. Dobermann, G.C. Simbahan, and H.C. Gines Highly variable soil nutrient supplies within small localities, low efficiencies of applied fertilizer nitrogen, and unbalanced nutrition are major constraints to increasing productivity in irrigated lowland rice systems of South and Southeast Asia. A new concept for site-specific nutrient management (SSNM) was developed to overcome these constraints. Using this approach, fertilizer recommendations can be worked out on a field-specific basis to account for the variability in indigenous nutrient supply. Data from a case study in the Philippines are presented showing an average increase in grain yield of about 11% because of SSNM in comparison with the farmer's fertilizer practice (FFP) under current management practices. SSNM performed better than FFP regardless of yield constraints related to general crop management or pests. Results also indicated a substantial scope for further increases in productivity, if different aspects of crop management were improved simultaneously (such as pest and disease control and nutrient management). We highlight the importance of strategic on-farm research to collect primary data for model development at the farm level, covering a much wider range of environmental and socioeconomic conditions than possible through on-station research only. A conceptual model is presented for integrating crop and pest management into a nutrient decision support system for irrigated rice. Wang Guanghuo, A. Dobermann, C. Witt, Q. Sun, R. Fu, G. Simbahan, and M.A.A. Adviento The climate-adjusted, genetic yield potential of modern rice varieties in Zhejiang Province of China is currently about 10-12 t ha-1. Attainable yields in farmers' fields, however, have been maintained at only about 5.5-6.0 t ha-1 in both the early and late cropping seasons since 1985 despite the large-scale use of hybrid and other modern rice varieties and increasing fertilizer use. On-farm experiments involving 21 rice-growing farmer families began in 1997 in the central part of Zhejiang Province to assess the status of soil fertility and productivity under intensive rice-rice cropping. Low and variable recovery efficiencies of applied inorganic fertilizer nitrogen were identified as a major constraint to increasing plant nutrient uptake and grain yield in farmers' fields. A new, site-specific nutrient management strategy was developed to increase productivity and break the apparent attainable yield barrier of 6 t ha-1. Field- and season-specific fertilizer recommendations were calculated considering indigenous soil nutrient supply, reasonable grain yield targets, and corresponding nutrient demand, nutrient balance, and nutrient-use efficiencies. The agronomic performance of SSNM was tested on the 21 farms against the farmer's fertilizer practice (FFP) in 1998 and 1999. Across seasons and years, grain yield was 8% greater with SSNM than with FFP (6.35 vs 5.90 t ha-1), whereas plant N, P, and K uptake increased by 8-14%. The gross return over fertilizer cost was about 10% greater with SSNM than with FFP (US$998 vs $905 ha-1 crop-1). In general, yields were about 1 t ha-1 or 19% greater in late rice (July to October, mostly hybrid cultivars) than in early rice (April to July, mostly inbred cultivars), but SSNM performed equally better than FFP in both seasons. Since fertilizer N, P, and K rates were lower in SSNM, especially in 1999, increases in grain yield and nutrient uptake were most likely due to improved timing and splitting of fertilizer N, which increased the average recovery efficiency of applied fertilizer N from 0.19 kg kg-1 in FFP to 0.29 kg kg-1 in SSNM. The average agronomic N-use efficiency (grain yield increase per kg fertilizer applied) was 80% greater with SSNM than with FFP (11.4 vs 6.3 kg kg-1). However, N-use efficiencies were generally low, thus indicating further scope for improving N management strategies. Water and Weed Management in Direct-Seeded Rice Water and weed management in direct-seeded rice: Are we headed in the right direction? J.E. Hill, A.M. Mortimer, O.S. Namuco, and J.D. Janiya Water management is commonly recognized as the single most important cultural practice determining the success or failure of weed control in rice. Transplanted rice evolved in large part to allow the use of early flooding as a means of weed control. However, as the cost of labor rises, South and Southeast Asian farmers have moved increasingly to direct seeding; yet, paradoxically, direct-seeded rice in the tropics is difficult to establish under early or continuous flooding. Early or extended field drainage to facilitate root growth and anchorage of the rice seedling almost always results in moderate to dense weed infestations. Furthermore, the time and extent of drainage greatly influence the weed species composition and abundance. Drainage and shallow flooding early in the life of the crop generally promote germination and growth of grass weed species such as Echinochloa and Leptochloa, whereas continuous flooding encourages the aquatic broadleaf weeds such as Monochoria vaginalis. Thus, the conversion from transplanted to direct-seeded rice results in a more competitive weed flora and increases reliance on herbicides for their control. The problem of delayed flooding or draining to establish direct-seeded rice is further compounded by poor field leveling and water control systems throughout much of Asia. Even where fields are flooded, the difference of only a few cm in water depth can substantially change the weed flora. Poorly leveled fields and the inability to move water quickly on and off contribute to variability in both rice stand establishment and in weed species. We review the available evidence and discuss research directions and priorities. We conclude that research and technology development at the interface of weed science and water management should focus on (1) a better understanding of the relationship of water depth and drainage to weed recruitment, (2) mechanisms to improve rice seedling survival and emergence under flooding, (3) improvement of infrastructure at the field scale to allow for pinpoint flooding and uniform water depth, and (4) knowledge-based decision support systems for farmers to fully integrate weed management practices. Economical use of water for direct-seeded rice R. Balasubramanian, J. Krishnarajan, and S. Ramesh The need for greater food production at prices affordable by consumers and profitable to farmers with emphasis on natural resources and the environment has been of prime concern to all people. Rice is the staple food of half the world. Rice production must increase from 500 to 800 million t in the next 25 years to meet projected world rice demand. It is estimated that per capita availability of water, about 85% of which is used in agriculture, has declined by 60% from 1950 to 1990. A water crisis for rice is fast approaching. India, Pakistan, and the Philippines are particularly expected to suffer a sharp decline in per capita water availability over the next two decades. Rice production systems are rapidly changing due to the declining availability of water resources for agriculture. Direct seeding is being practiced increasingly to cope with the reduced availability of irrigation water. The water-use efficiency of rice is much lower than that of other crops. On average, more than 5,000 liters of water are used to produce 1 kg of rice. In irrigated wet-seeded rice culture, water-use efficiency on the farm can be increased by applying only the amount of water needed. This needs more research to economize on water use. It is in this context that studies were begun on the irrigation requirement of direct-seeded rice versus transplanted rice. This study focused on reducing the water requirement and improving its use efficiency in wet-seeded puddled lowland rice. Field experiments were conducted at Tamil Nadu Agricultural University, Coimbatore, India, during the kharif and rabi seasons of 1997 in a randomized block design with nine levels of irrigation replicated three times. Irrigation levels significantly influenced the weed population and biomass in both seasons. Grain yield was the highest with irrigation at 5-cm depth 1 d after the disappearance of ponded water in direct-seeded rice, transplanted rice, and continuous submergence of 2.5 cm. Water use was the maximum with transplanted rice due to extended land preparation and nursery raising. Continuous submergence of 2.5 cm on wet-seeded rice recorded the highest water productivity and saved 25% and 24% versus transplanted rice (TPR) in the kharif and rabi seasons, respectively, without impairing productivity and net returns. Higher water productivity and considerable net returns and benefit:cost ratio clearly shows the scope for economizing on irrigation water by continuous submergence of 2.5 cm in wet-seeded rice. Hence, continuous submergence of 2.5 cm may be recommended for wet-seeded rice in lieu of 5 cm, which resulted in a 25% savings in irrigation water versus transplanted rice. M. Kondo, D.V. Aragones, P.P. Pablico, M. Hagiwara, T.P. Tuong, and M. Yamauchi Anaerobic seeding, wherein seeds are sown in puddled soil, has been developed to stabilize seedling establishment of direct-seeded rice. We carried out field and laboratory experiments at IRRI to investigate the factors affecting seedling establishment, agronomic performance, and yield in rice in broadcast and row-drilled anaerobic seeding and compared these methods with surface-broadcast direct seeding and transplanting. Early flooding severely lowered seedling establishment, which was further decreased by intensive tillage. Intensive tillage, early flooding, increased flooding depths, and incorporation of straw lowered seedling establishment. The reduced seedling establishment was related to the increasingly reduced soil redox potentials and probably to the increased concomitant Fe++ formation. High plant density in all direct-seeding methods led to vigorous vegetative growth in terms of dry matter production, tiller number, and N uptake. However, dry matter production and N uptake in direct seeding became inferior to those of transplanting after the reproductive stage, which resulted in comparable or lower total spikelet number and yield in direct seeding. Minimizing the decrease in spikelet number per panicle associated with increased panicle number and low N uptake after the reproductive stage is a critical factor in improving yield. Anaerobic broadcast seeding showed growth patterns similar to those of surface broadcast seeding. Anaerobic drill seeding showed comparable yield, higher N uptake, and slower leaf senescence after the ripening stage compared with anaerobic broadcast seeding. Establishment of irrigated rice under zero and conventional tillage systems in the Philippines C.M. Piggin, C.O. Garcia, J.D. Janiya, M.A. Bell, E.C. Castro, Jr., E.B. Razote, and J. Hill Zero-till establishment is used widely for many crops around the world. There has been some work on rice, but this was mostly before the development of broad-spectrum, nonresidual herbicides and direct-drill seeders. The technology has potential to allow savings in time, energy, water, and labor during crop establishment. This is important in Asia as labor and water shortages are becoming more important constraints in rice cropping. A long-term field trial to develop and evaluate a methodology for zero-till establishment of irrigated lowland rice was established in 1998 at the International Rice Research Institute (IRRI). Zero-till crops were established with small hand-tractor-mounted seeders, which placed the seed at 3-5 cm in either a narrow slit opened by a tyne or a narrow furrow opened by a rotovator. Zero-till treatments were compared with conventional treatments of direct dry seeding on cultivated soil or direct wet seeding with pregerminated seed on puddled soil. Various weed control strategies using preemergence (butachlor, oxadiazon, pretilachlor) and postemergence (bentazon, cyhalofop, 2,4-D) herbicides were evaluated under the different crop establishment treatments and compared with hand weeding and no weed control. Regular observations are being made on crop and weed growth, soil parameters, and water use. Some results on crop and weed growth for the first three seasons are discussed. Crop establishment and grain yield were comparable from zero-till and cultivated treatments, especially in the third season, when crop establishment and management technologies were better developed and yields of 5 t ha-1 were achieved. Hand weeding and various herbicide combinations were effective in controlling weeds, but weeds were abundant and yields dropped markedly to 0.1-1 t ha-1 where there was no weed control. There were 3-4 dominant weeds in a suite of 10-12 species in most treatments. Generally, Fimbristylis miliacea and Leptochloa chinensis were major weeds under all establishment treatments, Cyperus difformis and Scirpus maritimus were common under wet seeding, and Echinochloa colona and Ludwigia octovalvis were common on zero-till and dry-seeded plots. Results suggest that zero-tillage technology has great promise for the establishment of lowland irrigated rice. Further research is required to refine the machinery and technology for weed control, crop establishment, and crop management. Wet-seeded rice cultivation technology in Korea Je-Kyu Kim, Sang-Soo Kim, Sung-Tae Park, Yang-Soon Kang, Soon-Chul Kim, Moon-Hee Lee, and Shaobing Peng Since direct-seeded rice was first introduced in 1991, the area for direct seeding in 1995 increased to 117,500 ha, which is 11.1% of the total paddy field in Korea. There are two methods of direct seeding in rice: dry and wet seeding based on the physical condition of the field and seeds. In Korea, wet seeding is further divided into two types: wet drill seeding and water seeding. Water seeding is a technology in which pregerminated seeds are sown in standing water by a motorized seed sprayer. Wet drill-seeding technology was developed to solve the problems of water seeding such as unstable seedling stand and lodging. A wet drill seeder having six furrow openers with the operator riding on it was designed to make furrows by pressing the hardening paddy. The optimal seeding time is 1 May to 5 June, depending on the temperature at seeding time. For both drill and water seeding, the optimum seeding rate is 30-50 kg ha-1 and the optimum seedling stand is 80-120 seedlings m-2. The optimal nitrogen (N) application is 110-130 kg m-2. Recently, a furrow drill-seeding method was developed that is a combination of the dry and wet direct-seeding methods. To control weeds in wet-seeded rice, a one-shot application |