|
||
|
|
|
|
||
 |
 |
Exploiting biodiversity for sustainable pest managementProceedings of the Impact Symposium on Exploiting Biodiversity for Sustainable Pest Management, 21-23 August 2000, Kunming, China Approaches to a relevant understanding of biodiversity for tropical irrigated rice pest management Michael J. Way and Glicerio M. Javier, Jr. "We must grasp the essence of the thing, this is the only reliable and scientific method of analysis" Mao Tsetung 1930 The known biodiversity of tropical irrigated rice from the genetic to field community level is greater than that of any other arable crop or wild plant. At the genetic level, there have been outstanding successes in exploiting biodiversity in rice plant resistance to pests and in prospects through genetic engineering. Although these advances have largely been applied to nondiverse monocultures of particular cultivars, relatively few practical advances have been made in using genetic biodiversity as part of an integrated pest management (IPM) approach, such as manipulating the patterns of rice cropping to counter resistance-breaking strains of pests. Yu Xiaoping In the Yangtze River Delta, Saccharosydne procerus (Delphacidae: Homoptera) on the vegetable Zizania caduciflora L. is a major alternate host of the egg parasitoid Anagrus nilaparvatae (Mymaridae: Heteroptera), which is an important biocontrol agent of planthoppers on single-season japonica rice. A. nilaparvatae and related Anagrus species can overwinter in S. procerus eggs in Zizania fields during the rice off-season. In April, Anagrus spp. disperse to and build up on hopper hosts on newly transplanted rice fields. Most movements of Anagrus spp. were found between Zizania fields and rice during the early rice season, especially in June. In a free-choice test, A. nilaparvatae oviposited in and emerged from both S. procerus and the brown planthopper (BPH) Nilaparvata lugens eggs although it preferred BPH. Although parasitism of S. procerus by A. nilaparvatae was more than 15%, S. procerus could not complete its lifespan on rice, indicating no damage by this hopper to rice. This chapter shows that proper deployment of rice and Zizania fields will enhance the efficiency of the egg parasitoid A. nilaparvatae against both planthoppers in rice and S. procerus in Zizania fields. Habitat manipulation based on this research could be incorporated into integrated pest management in the temperate rice ecosystem. T.F. Marcos, L.B. Flor, A.R. Velilla, K.G. Schoenly, J.O. Manalo, O.M. Ofilas, P.S. Teng, J.R. Ulep, M.B. Tinguil, T.W. Mew, A.B. Estoy, L.G. Cocson, and S.R. Obien Pest and natural enemy abundances in rice and nonrice habitats along transects at Batac and Badoc were monitored to characterize herbivore and natural enemy assemblages in rice and surrounding nonrice habitats during different cropping seasons. The data were analyzed to determine arthropod associations, population shifts, and habitat compatibilities with rice. A bund management study was then made to validate characterization results and design a strategy whereby natural enemy action can be conserved and enhanced to reduce pest abundance. The characterization study yielded a total of 119 arthropod families with 363 confirmed taxa. At Batac, 120 herbivore and 158 natural enemy taxa were identified, whereas Badoc had 113 herbivore and 159 natural enemy taxa. Cicadellids were the predominant herbivores in both rice and nonrice habitats. Spiders, formicids, and coccinellids were the dominant predators and Mymaridae, especially Mymar taprobanicum, and the trichogrammatid Oligosita sp. were the dominant parasitoids. Natural enemies had the most taxa in most habitats. The measurement of habitat compatibility generally showed bunds and fallow similar to those of rice in terms of herbivore and natural enemy assemblages. Insect pests and natural enemies were more abundant and had more taxa in rice paddies with weeds on bunds than in paddies without bund weeds. They were also more abundant in bunds than in paddies. Natural enemies were most abundant in bunds with only broadleaf weeds. Among the 36 species of weeds monitored in bunds, seven-Alysicarpus vaginalis, Sphaeranthus africanus, Vernonia cinerea, Ipomoea triloba, Heliotropium indicum, Digitaria sanguinalis, and Ischaemum rugosum-were associated with insect pests, whereas all species except A. vaginalis harbored natural enemies. Where the bund weeds Panicum repens, Cynodon dactylon, Dichanthium aristatum, and Commelina diffusa were infected with sheath blight, the adjoining edges of rice paddies were sometimes also infected. The results indicate that some other crops, notably cowpea, are especially important reservoirs of natural enemies of rainfed rice pests during the nonrice season. So, appropriate crop manipulation might be feasible for enhancing the role of insect natural enemies in integrated pest management of rice. Similarly, it is evident that bund manipulation, particularly the enhancement of broadleaf weeds, can provide vital sources of insect natural enemies as well as prevent the spread of rice sheath blight from grassy hosts on bunds. Liu Guangjie, Lu Zhongxian, Tang Jian, Shen Junhui, Jiang Yaonan, Zheng Xiusong, Yang Baojun, Chen Jianming, Xu Hongxin Population changes of major insect pests, natural enemies, and detritivores in rice habitats were monitored at monthly intervals in insecticide-free and insecticide-treated habitats for an entire rice season. Based on our present studies with temperate japonica rice, the following conclusions could be drawn: 1. Soybean neighboring paddy fields is a beneficial habitat for conserving natural enemies of insect pests of rice without sharing the insect pest species with the rice habitat. 2. Planting planthopper-resistant rice varieties without early sprays of insecticide could effectively and efficiently suppress pest populations. 3. Decreasing numbers of insecticide sprays in an entire rice season is possible and acceptable though this needs to be examined further by more detailed work. L.P. Lan, N.P.D. Huyen, N.H. Quang, and N.V. Minh The relationships between components of rice and nonrice habitats were examined in relation to rice pest management based on ecology and biological control. The diversity of flora and fauna was therefore investigated on a 10-km transect along the Kinh Xang canal in Chau Thanh and Tan Phuoc District (Tien Giang) in the Mekong Delta, Vietnam. The crops included rice monocultures and nonrice multicultures of two to three crops per year from September 1997 to December 1998. Overall species components of the nonrice habitats were more diverse, but the development of the arthropod population was more stable in the rice habitats than in other individual crops. There were about 253 species in the rice field and 283 in the nonrice habitat. Many species of arthropods exist concurrently in two habitats. Similarity indices changed with the rice growth stage, from (0.5 at the tillering stage to (0.5 at the ripening stage. Homoptera Auchenorrhycha contributed a large component to the total of arthropods collected in rice and nonrice habitats. Cicadellidae were less abundant than Delphacidae and there were large populations of spiders and other predators in both rice and nonrice habitats. The floral diversity of nonrice habitats around rice fields is considered to be important in biological control of rice pests. The role of microbial immigration in disease management by enhancement of plant diversity Steven E. Lindow The process of immigration of microbes to plants will be discussed in the context of establishing inoculum of plant pathogenic bacteria on plants. Bacteria of all types move freely from one plant to another and inoculum of a plant pathogen frequently originates in distal plants. Subsequent multiplication of bacterial cells on leaf surfaces can establish a large epiphytic population size that is required before infection can occur. The use of plant variety mixtures ensures that the initial immigrants to a plant are a diversity of microorganisms, only a small proportion of which might be pathogenic to that plant. This reduces the likelihood that the initial immigrants to a leaf are compatible pathogens and therefore reduces the probability that such pathogens can establish a population large enough to cause disease. The local plant composition can therefore strongly influence the composition of microbial communities on a plant. Sheath blight management with antagonistic bacteria in the Mekong Delta P.V. Du, N.T.P. Lan, P.V. Kim, P.H. Oanh, N.V.Chau, and H.V. Chien A survey of sheath blight (ShB) disease and antagonistic bacteria on nonrice plants, soils, and rice seeds was conducted for one year starting in August 1997 at a "lighthouse" site in Tien Giang Province. Seventy-two isolates of sheath blight showed 5 morphotypes of colony appearance and 4 anastomosis groups that belong to AG 1 with 11 isolates, AG 2-2 with 2 isolates, and AG 4-HG-1 with 1 isolate. Another 50 isolates did not show any type of anastomosis with AG tester isolates; therefore, these isolates were temporarily grouped as AG-UNK. Pathogenicity testing determined that all sheath blight isolates found on 32 weed species can infect rice. The main source of sheath blight inoculum is water contaminated with sclerotia; mycelium in rice plant debris can also act as a primary source. The possibility of employing antagonistic bacteria to control sheath blight was studied. Approximately 1,000 strains of beneficial bacteria were isolated from seeds and other rice components; 10 of these possessed high levels of antagonistic properties and enhancement of plant growth. The selected strains significantly reduced sheath blight development and spread in both greenhouse and field conditions. Four strains, NF49, NF52, TG17, and TG19, were particularly active. A mixture of two strains in a ratio of 1:1 gave significantly better control of the disease than each of the strains used individually. Under conditions of high disease pressure, however, an antagonistic formulation amended with Validacin 5SP (validamycin) at 25% of the recommended rate has been shown to increase the efficacy of biological control of Rhizoctonia solani in natural conditions. To maintain an effective density of biological control agents (BCA) on the rice plant surface, bacterial suspension should not be applied before the maximum tillering stage because the ShB pathogen rarely works at that time under flooded paddy soil conditions. To enhance BCA in the rice field, weed management should be linked with water management and crop residue management to limit incoming inoculum sources. Demonstrations of BCA application for the suppression of sheath blight disease in rice farmers' fields have been conducted and will be continued. The optimization of fermentation and suitable formulations with low production costs need to be assessed to scale up the technology. Biological control agents against major pathogens of rice in the Yangtze Delta area of China Xie Guanlin, Yu Xuefang, Ren Xiaoping Biocontrol agents (BCA) of bacteria from rice of three cultural patterns (direct row seeding, direct broadcast seeding, and transplanting) were evaluated, detected, and identified in the Yangtze Delta area of China during 1997-2000. Some 8,993 nonpathogenic bacterial isolates were isolated from 1,050 samples of leaf sheath and grain of rice collected at six different growth stages and tested for antagonistic effects against major pathogens of rice. The number against Rhizoctonia solani was the highest. Seed yielded the lowest number among the three parts of the rice plant. The population of BCA decreased with rice plant maturity in the three cultural patterns. A higher fluctuation of the BCA population was noted in some stages in each cultural pattern. The higher number of BCA detected was closely related to the severity of rice sheath blight in the field. Some promising BCA were found in field evaluations against sheath blight and bakanae disease of rice. Seven genera of 17 species or types were involved in antagonistic activity against the six major pathogens of rice. Populations of rice sheath blight in the Ilocos Norte rice-based ecosystem J.O. Manalo, T.W. Mew, P.S. Teng, A.R. Velilla, and E.S. Borromeo A total of 378 isolates from plants and soil were collected in Batac and Badoc, Ilocos Norte, Philippines. Comparisons between the two populations based on pathogenicity, anastomosis, and DNA banding pattern were made. Major differences in the isolates were evident in all the tests performed, indicating that the soil and plant populations are separate strains. Plant isolates were virulent to IR64 rice and 88.4% of these were vegetatively compatible with the AG 1 isolate. Soil isolates, however, were generally nonpathogenic and did not anastomose with the AG 1 from rice. Molecular characterization confirmed that the soil isolates were a different strain, although morphological features closely resembled those of the Rhizoctonia spp. Characterization tests of the isolates suggest that the predominating Rhizoctonia-like isolate in the Ilocos Norte soil is not damaging to the rice crop. Primary sources of infection were believed to be the weeds along the bunds and maize that was grown in sequence with rice. Cluster analyses indicated that the isolates from plants were homogeneous throughout the sites regardless of the host sources, but grouping tendencies can be observed as the isolates move closer to each other along the transect. Spread of the disease in the field is apparently within the canopy through plant-to-plant contact. Identification of important weed species was included in this study. Bacterial antagonists against Rhizoctonia solani AG 1 in irrigated rice ecosystems Wanzhong Tan and T.W. Mew Bacterial antagonists against the rice sheath blight pathogen, Rhizoctonia solani AG 1, were estimated in irrigated rice ecosystems and their potential for disease management was evaluated. Bacterial isolations were done using an improved method of trapping bacteria from the washings of plant tissues, paddy soil, and weeds in and around the field. Total and antagonist populations varied with source of isolation and collection sites. A majority of the 4,780 bacterial isolates obtained were isolated from rice plant tissues with the leaf blades and sheath harboring a higher proportion. Eighty-seven percent (4,159 isolates) of these bacteria were neutral to the pathogen, 12.8% (613 isolates) showed antagonism, and only 0.27% appeared to promote pathogen growth. Ninety percent of the antagonists exhibited strong inhibition to the fungal pathogen either by inhibiting the germination of pathogen sclerotia or by inhibiting the size of the colonies in agar media. Similarly, these antagonists also affected germination and seedling growth of the rice plant to various degrees. A total of 91 isolates demonstrated strong inhibition to the pathogen but promoted rice seed germination and seedling vigor. Evaluation of the effectiveness of these antagonists for sheath blight management revealed that population density, pathogen inoculum level (disease pressure), and crop management practices such as time of application of antagonists or spray of fungicides are factors that influence the efficacy of the antagonists. The data also suggest that the value of antagonist application for sustainable sheath blight management may lie more in its potential to reduce inoculum efficiency, resulting in a decrease in infection foci and limited disease spread. Varietal diversification and disease management Christopher C. Mundt One of several strategies to extend the longevity of host-plant resistance is to grow mixtures of plants that possess different race-specific resistance genes. After many years of discussion, the diversity approach is beginning to be applied in commercial agriculture. The efficacy of mixtures for disease control is affected by spatial scale, with mixtures performing better in commercial production than in small-scale experimental plots. Limited field observations have not detected rapid selection for pathogen races with multiple virulence genes in host mixtures, though mixtures should be managed to avoid such an occurrence. Identification of useful variety combinations with functional diversity requires knowledge of both host and pathogen populations, as well as significant field testing. Diversity of crops, diversity of people, and diversity of lighthouse approaches are all needed, at different spatial scales, to contribute to the sustainability of disease management through host diversity. Rice blast control with multilines in Japan Shinzo Koizumi The current situation of rice blast control with multilines and its studies in Japan are summarized for durable and effective control of the disease. From 15 different recurrent rice cultivars, near-isogenic lines with different genes with complete resistance to blast have been developed or are being developed to control the disease in Japan. One group of these, the Sasanishiki multilines, has been registered and cultivated in northern Japan. Mechanisms of blast reduction in multilines are also discussed. A reduction in susceptible plants, the barrier effect of resistant plants, and induced resistance are considered to contribute to blast reduction in multilines and cultivar mixtures. The effectiveness of the Sasanishiki multilines for blast control and the changes in blast races in them were investigated. Results indicated that an increase in the number of components and proportion of resistant components is necessary for effective blast control with multilines. Since available genes with complete resistance to blast are limited in Japan, multilines with high levels of partial resistance are required. Current status and prospects of mixture planting for control of rice blast in Yunnan Zhu Youyong, Chen Hairu, Fan Jinghua, Wang Yunyue, Li Yan, Chen Jianbing, Li Zuoshen, Zhou Jinyu, Fan JinXiang, Yang Shisheng, Maguang Liang, Hu Lingping, Christopher C. Mundt, E. Borromeo, Hei Leung, and T.W. Mew Under the project funded by the Asian Development Bank on "Exploiting Biodiversity for Sustainable Pest Management," scientists from the Philippines-based International Rice Research Institute (IRRI) and the Yunnan Agricultural University began a farmer participatory project to control blast by diversifying varieties in farmers' fields. Large-scale field tests for two consecutive years showed that the highly susceptible glutinous rice varieties (Huangkenuo and Zinuo) suffered less disease when interplanted with the generally resistant indica hybrid varieties (Xianyou 63 or Xianyou 22). The field design was a repeating pattern of one row of glutinous rice interplanted with four or six rows of indica rice. Helped by a vigorous extension campaign, farmers in Yunnan rapidly adopted the scheme, with area planted to the mixture now covering 42,500 hectares. This rapid adoption can be attributed to strong support from technicians and leaders of counties, relevance to the needs (problems) of farmers in the area, simplicity and effectiveness of the technology, and improvement in the yield and income of farmers. Plans are now in place to implement the technology in other provinces of China, and to widen the options for varieties that can be used for diversification. Biodiversity of blast pathogens and implications for blast management Prasartporn Smitamana, Phrek Gypmantasiri, Wasana Phumsathit, Suphan Panyafoo, Chuanpit Boonchitsirikul, and Acharaporn Na Lampang Rice blast, caused by Pyricularia grisea Sacc., is so diverse that it makes control of the disease difficult. Research on the host range, biodiversity, and interaction of various rice genes with resistance to this fungus was carried out in Chiang Mai, Thailand. Leptochloa chinensis and Panicum repens were found to be potential hosts and served as sources of inoculum. Results from the DNA fingerprinting of the 90 blast isolates selected from 597 isolates obtained from rice, weeds (Brachiaria mutica, Digitaria sanguinalis, Eleusine indica, Pennisetum polystachyon, Panicum repens), and barley confirmed that certain weed isolates were classified in the same group as those from rice. Moreover, some were 90% similar to rice isolates. Although the barley isolates were totally different from those of rice, they were 75% similar to P. repens isolates and 70% similar to E. indica and D. sanguinalis isolates. The barley isolates, however, could infect rice under glasshouse conditions; therefore, growing susceptible rice varieties after or near barley should be avoided. Testing 23 selected blast isolates against a set of IRRI's near-isogenic lines containing 16 resistance genes showed that Pita, Pik-p, and Pita-2 were resistant to the tested isolates, thus indicating their possible use in rice breeding programs. Yi-jun Zhou, Yong-jian Fan, Fan Lu, Zonghua Wang, E. Borromeo, Hei Leung, Shu-hua Wu, Da-fu Yan, Jia-lu Hua, Zhao-bang Cheng, Wen-hui Zhang, Jian-an Ji, Zhi-yi Chen, Yong-feng Liu, Yi-ren Chen Based on reactions on 7 Chinese rice differential varieties, 7 race groups and 11 races of Magnaporthe grisea were detected from rice in Jiangsu Province located in the Yangtze Delta of East China in 1997-99. Race group ZG has always been dominant since 1993. Most of the tested isolates of M. grisea can overcome resistance of Pik-s, Pit-a2, Pit, and Pit-a genes. DNA fingerprints of M. grisea by rep-polymerase chain reaction (PCR) showed that all tested samples from Jiangsu could be amplified by 6(17 bands and 23 bands were scored in cluster analysis. A dendrogram demonstrated that tested isolates could roughly be classed in 6(7 similarity genetic groups (lineages) at a 55% similarity level by cluster analysis of M. grisea DNA fingerprints. Resistance gene Piz-t demonstrated resistance to all seven typical Chinese races and was very significant for rice production in Jiangsu. Resistance gene analog (RGA)-PCR analysis of 59 varieties from Jiangsu (65(90 bands scored) showed abundant polymorphism. A mixture-variety-planting experiment with five varieties with a markedly different genetic background and different resistance demonstrated different rules of regulating blast disease. Control effects varied among different variety groups and the maximum reached 46(97% compared with susceptible variety Suyunuo. Eleven races included in 6 race groups were identified from Wujiang in 1980-94. Data on the resistance reaction of rice differential varieties in Wujiang show that race variation is almost identical to that of artificial inoculation. Serious susceptibility of Tetep from 1989 to 1991 is relative to race group ZA. Xiushui 04 and others with gene Pit-a2 or Pik-m easily lost resistance after cultivation for 1(4 years. Variety 93-31 and others with the Piz-2 gene present maintained their resistance. The recent use of resistant varieties in Wujiang is also a cause for the low occurrence of rice blast. Prospects of a marker-aided varietal diversification strategy for disease control Emerlito Borromeo, Wang Zhonghua, Zhu Yijiun, Yun-yue Wang, Zhu Youyong, and Hei Leung Polymerase chain reaction (PCR) primers corresponding to the conserved motifs of prototype resistance genes were used to characterize germplasm in traditional and current commercial varieties that are candidates for varietal diversification. The predictive value of PCR markers on the phenotypic expression of disease resistance among the germplasm was evaluated. Our results showed that, although the markers were useful in grouping genetically related germplasm and varieties, they are not sufficiently predictive of specific resistance phenotypes. Based on analyses of segregating populations from other controlled crosses, we conclude that specific sequences corresponding to candidate resistance or defense genes have better potential for predicting functionality. Farmer scientists in IPM: a case of technology diffusion Peter A.C. Ooi, Warsiyah, Nanang Budiyanto, and Nguyen Van Son In the past decade, farmer education through an integrated pest management (IPM) field school approach has been recognized as an effective way to help farmers better understand the complex agroecosystem they have to work in. An important aspect of sustaining the knowledge gained in the field school is to encourage farmers to continue doing research. Such follow-up activities of the FAO Programme for Community IPM in Asia have resulted in many cases of farmers making informed decisions on matters relating to pest management in their villages. Three case studies are discussed to highlight the role of farmer scientists in facilitating technology diffusion. The first case study refers to farmer studies in Dalat, Vietnam, that led to an understanding of the selective action of the microbial insecticide Bacillus thuringiensis in managing the diamondback moth. With the information from experiments and pilot studies, farmers were able to contemplate organizing village-wide activities to conserve the population of Diadegma semiclausum, a key larval parasitoid of Plutella xylostella. This is only possible with the support of the local government and IPM trainers. The second case study concerns rat management in Kalensari village, Indramayu District, West Java, Indonesia, where farmers were able to mobilize local residents to reduce the rat population by catching the rats at night and feeding them to ducks. Reducing rat populations to very low levels before the planting season resulted in very low rat populations and hence less damage to the crop. The third case study provides an example of farmers working with IPM trainers in setting up a farmer learning facility in Sleman District of Yogyakarta, Indonesia. Rice farmers experimented with growing vegetables and enhanced their understanding of soil, microbials to manage insects and plant pathogens together with evaluating new cultivation practices. These three case studies reflected the strategy of the FAO Programme in promoting science and farmers. It has resulted in farmers who are more confident in solving field problems. These farmer scientists also share their knowledge with other farmers in the spirit of technology diffusion. Imelda M. Revilla, Jinxiang Fan, Youyong Zhu, Zuoshen Li, Twng Wah Mew, and Mahabub Hossain This chapter presents an overview of the technology adoption and diffusion of mixture planting in Yunnan Province, promoted by a China-IRRI collaborative research project, and assesses its impact on pest management and farmers' income. One hundred four farmer-adopters of mixture planting in four villages and 30 nonadopters from three villages of Shiping and Jianshui counties, Hong He Prefecture, were personally interviewed between 12 and 28 July 2000 to generate information on household characteristics, farm management practices, input use, yield, costs, and income. Data were then analyzed using "before and after" and "with and without" project comparisons to determine the impact of mixture planting. The rapid adoption of mixture planting can be attributed to a vigorous and systematic scheme implemented by the Yunnan Plateau lighthouse team in collaboration with the local extension agency. Results show that farms under mixture planting have a lower incidence of blast disease and farmer-adopters on average spend only $10.50 ha-1 for pesticides compared with nonadopters' pesticide cost of $42.92 ha-1 in 1999. Farmer-adopters had higher yields in 1999 than in 1996. In comparison with the yield on nonadopters' farms, glutinous rice yield is 84% higher on mixture farms. The yield of hybrid rice was almost the same with 20% less land that was reallocated to plant one row of glutinous rice in between four rows of hybrid rice. Overall, the yield was 7% higher and gross return was 14% more since the price of glutinous rice, because of its higher quality, was twice that of hybrid rice. The net gain in farm-operator surplus was estimated at 25%. Farmers' perceptions of the impact of mixture planting in general tend to support the quantitative analyses done for this study. |
|
|
|
Approaches to a relevant understanding of biodiversity for tropical irrigated rice pest management The role of microbial immigration in disease management by enhancement of plant diversity Sheath blight management with antagonistic bacteria in the Mekong Delta Biological control agents against major pathogens of rice in the Yangtze Delta area of China Populations of rice sheath blight in the Ilocos Norte rice-based ecosystem Bacterial antagonists against Rhizoctonia solani AG 1 in irrigated rice ecosystems Varietal diversification and disease management Rice blast control with multilines in Japan Current status and prospects of mixture planting for control of rice blast in Yunnan Biodiversity of blast pathogens and implications for blast management Prospects of a marker-aided varietal diversification strategy for disease control Farmer scientists in IPM: a case of technology diffusion A synthesis of two knowledge-based approaches to pest management |
|
|
|
