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Rice tungro disease managementRICE TUNGRO DISEASE MANAGEMENT Proceedings of a workshop, 9-11 Nov. 1998, Los Baños Laguna, Philippines Edited by T.C.B. Chancellor, O. Azzam, and K.L. Heong Rice tungro disease in the Philippines X.H. Truong, E.R. Tiongco, E.H. Batay-an, S.C. Mancao, M.J.C. Du, and N.A. Juguan The rice tungro disease scenario in the Philippines, research trends, and current extension activities are briefly explained and discussed in this paper. Farmers' perceptions and knowledge on the subject were also included because farmers make decisions for sustaining farm income and protecting the agroecosystem. Some farmer groups have used green leafhopper (GLH)-resistant varieties for the past several years through the SeedNet and Farmers' Field School, yet rice tungro disease (RTD) remains a major constraint to rice production. For the first time in rice technology development, rice tungro virus (RTV)-resistant advanced breeding lines were identified. A few farmers in RTD-endemic areas evaluated these lines on their farms. Seeds of these lines with yields of 3.5-4.5 t ha-1 are being increased and will be deployed as stopgap materials for farmers during the wet season. Some progress had been made in understanding the genotypes of tungro viruses present during recent RTD outbreaks, and the role of cropping practices and infective GLH or virus inoculum during the past RTD outbreak in Mindanao. More collaborative efforts in research and extension have to be undertaken to strengthen farmers' decision making for appropriate RTD management in the context of a sustainable farming system. M. Arboleda, F. Sta. Cruz, and O. Azzam A basic understanding of tungro virus populations is a prerequisite for any deployment strategy of conventional or transgenic virus resistance. In the 1996 and 1997 wet seasons, the genetic variability of rice tungro bacilliform virus (RTBV) field populations was monitored in Isabela and North Cotabato provinces of the Philippines. Based on restricted genome DNA profiles and Pearson's correlation coefficient analyses, heterogeneous and distinct RTBV populations were identified in the two provinces. Although members of the populations reoccurred in some sites, the combination of genotypes differed significantly over time, suggesting a rapid evolution of the virus population. This study shows that changes in virus populations need to be continuously monitored to better understand and predict tungro outbreaks and to prolong the life of deployed resistance genes. Preliminary analysis of genetic variation of rice tungro spherical virus in the Philippines K.M.L. Umadhay, M.L.M. Yambao, and O. Azzam This study investigates the genetic variability of rice tungro spherical virus (RTSV) in nine tungro-endemic sites of the Philippines and over the 1996 wet season and 1997 wet and dry seasons. Based on a reverse transcriptase-polymerase chain reaction technique (RT-PCR) followed by restriction enzyme analysis, six distinct genotypes of RTSV were identified and their frequency across all sites determined. Results showed that more than one genotype could exist in a plant and at least two RTSV genotypes are present at one site. Although RTSV population did not change during the sampling, the presence of mixed infections and minor genotypes suggest that the structure and composition of the virus population is not stable. It is essential to continue monitoring these populations over an extended period to identify factors that lead to virus outbreaks or extinction of the current prevailing populations. This approach is critical in achieving durable virus resistance. Breeding for rice tungro disease resistance at PhilRice L.S. Sebastian, E.R. Tiongco, D.A. Tabanao, G.V. Maramara, S. Abdula, and E.B. Tabelin Breeding for resistance to rice tungro disease is a major objective of the rice breeding program for irrigated lowland and rainfed ecosystems at the Philippine Rice Research Institute. Tungro-resistant donors are identified using visual screening and serological assays and are then crossed with selected high-yielding modern genotypes with good grain quality. Field evaluation of advanced breeding lines is carried out at experimental stations in Nueva Ecija and in North Cotabato. Methods for generation advance and resistance screening are described. As of the 1998 wet season, several F8 lines from the following crosses showed good resistance to tungro: PSB Rc4 × TI-11-8, BPI Ri10 × TI-11-8, IR64 ×TI-11-8. Molecular markers are currently being used to map resistance genes to tungro from Utri Merah and Utri Rajapan and molecular techniques are being developed to characterize strains of rice tungro spherical virus. Breeding for rice tungro virus resistance in Indonesia A.A. Daradjat, N. Widiarta, and A. Hasanuddin Breeding for rice tungro resistance is one of the major objectives of the rice breeding program in Indonesia. Early studies were directed toward developing rice varieties with good plant type, high yield, and resistance to the green leafhopper (GLH) vector. In recent work, the breeding objectives were redefined to consider two additional traits: grain quality and resistance to tungro viruses. A vigorous hybridization program involving several cultivars with high yield, good plant type, excellent grain quality, and resistance to tungro viruses was implemented. From the initial work, several high-yielding rice varieties with resistance to GLH have been released. Preliminary results from this study indicated that 2,296 accessions have strong resistance to tungro viruses. Based on the range of infection rates with tungro on single-cross populations, it was observed that Utri Merah, Tjempo Kijik, Seratus Hari T36, and M1085c-10-1 were effective donors of tungro resistance. Membramo was the best combiner of the donor cultivars, with high yield and excellent grain quality. The reaction of advanced breeding lines to tungro infection varied with disease pressure and vector population in the area. Genetic engineering of rice for tungro resistance O. Azzam, A. Klöti, F. Sta. Cruz, J. Fütterer, E.L. Coloquio, I. Potrykus, and R. Hull
Genes encoding sense and antisense viral coat proteins, polymerases, and proteases have been successfully used to engineer resistance to several plant viruses. In this study, viral genes of rice tungro bacilliform virus and the coat protein 3 of rice tungro spherical virus were used to engineer resistance in rice against tungro infection. Rice varieties such as IR64, TN1, Taipei 309, and Kinuhikari were successfully transformed and fertile transgenic plants were evaluated at T1 and T2 generations for their ability to confer protection against tungro infection using insect inoculation assays. Unfortunately, none of the 71 transgenic lines tested provided protection against tungro infection. Possible factors for the lack of protection are discussed.
Multilocation evaluation of advanced breeding lines for resistance to rice tungro viruses R.C. Cabunagan, E.R. Angeles, S. Villareal, O. Azzam, P.S. Teng, G.S. Khush, T.C.B. Chancellor, E.R. Tiongco, X.H. Truong, S. Mancao, I.G.N. Astika, A. Muis, A.K. Chowdhury, V. Narasimhan, T. Ganapathy, and N. Subramanian Twelve advanced breeding lines with different sources of resistance against rice tungro viruses were tested together with checks IR62 and IR64 in replicated 8 × 8-m plots at six locations in the Philippines, Indonesia, and India from 1995 to 1998. Advanced breeding lines with resistance derived from Utri Merah (IRGC accession no. 16680) had the lowest infection with rice tungro bacilliform virus and rice tungro spherical virus in each of the three countries, suggesting that the resistance is likely to be effective in a wide range of locations. Some of these lines also had promising yield potential. Two lines derived from ARC11554 (IRGC accession no. 21473) showed promising results in the Philippines and Indonesia but not in India. Prospects of virus-resistant varieties for controlling rice tungro disease in Bali I.G.N. Astika Rice tungro disease has been an important constraint to rice production in Bali, Indonesia since 1980. Tungro incidence is favored by staggered planting dates and the cultivation of susceptible varieties such as IR64 and Krueng Aceh. Since 1995, virus-resistant lines bred at IRRI have been evaluated in replicated field trials in Celuk Gianyar Province. One line with resistance from Balimau Putih, IR68305-18-1, showed useful tolerance to infection. It has proved to be popular with farmers in Karangasem Regency because of its good eating quality and it is now grown widely in this area. Two lines derived from Utri Merah have shown strong resistance in field trials. None of these lines, however, are commercially available as they have not yet been cleared for varietal release. Evaluating rice germplasm for resistance to rice tungro disease in West Bengal, India A.K. Chowdhury Rice tungro disease is a recurrent problem in areas of West Bengal, India where rice is grown continuously. Rice germplasm developed at IRRI with resistance to tungro viruses were evaluated from 1995 to 1998 at the Regional Rice Research Station of Bidhan Chandra Krishi Viswavidyalaya at Chakdah. Line IR69705-1-1-3-2, with resistance derived from Utri Merah, had consistently low infection with rice tungro spherical virus and rice tungro bacilliform virus in three trials. IR68305-18-1 has a good plant type and excellent eating quality and is also considered to be a promising line. The deployment of tungro-resistant varieties is considered to be the most important strategy for managing tungro disease in the future. Rice tungro disease resistance and management in Tamil Nadu, India N. Subramanian, T. Ganapathy, M. Surendran, and A. Azeez Basha Major outbreaks of rice tungro disease occurred in Tamil Nadu in 1984 and 1992 and the disease has continued to appear sporadically in certain districts. Varietal resistance was identified as the most appropriate strategy for managing tungro and collaborative activities were initiated to evaluate the performance of advanced breeding lines with resistance or tolerance to tungro viruses. Field trials were conducted at the Rice Research Station of Tamil Nadu Agricultural University at Tirur in 1996-98 and several promising lines were identified. One tungro-tolerant line, IR68305-18-1, performed well in participatory trials with farmers and is now being used in a resistance breeding program at Tamil Nadu Agricultural University. Tungro screen kits for extension agents and plant breeders O. Azzam, L. Kenyon, and P.D. Nath For the last 14 years, IRRI has used the enzyme-linked immunosorbent assay (ELISA) method to screen and evaluate rice germplasm for tungro resistance and tolerance. Unfortunately, due to a lack in resources and technical capacities, this technology has not been taken up by national programs. Two years ago, collaborative activities between IRRI and NRI were initiated to develop diagnostic kits that are simpler and more suitable to the needs of national breeding programs and extension services. In this study, we report on the successful development of a Tungro Screen Kit for rice tungro bacilliform virus, one of the two viruses that cause the tungro disease. Five prototype Tungro Screen B kits were assembled and distributed at the Tungro Management Workshop held at IRRI in November 1998 for field testing in India, Indonesia, and the Philippines. Are tungro disease counts repeatable? K.G. Schoenly Scientists often assume that the measurements they take are repeatable across observers and sites; however, experience from different and unrelated disciplines indicate that interobserver repeatability varies with the sophistication of the measurement, observer experience, and the measurement scale used. Recent developments in repeatability methodology from quantitative genetics, for example, has produced an easy-to-interpret repeatability index R that varies from 0 (no repeatability) to 1 (perfect repeatabilty) derived from a one-way ANOVA (or intraclass correlation) that may be useful for plant protection workers. For measurements that are repeatable across a range of observers, the upper confidence interval for R (e.g., 95%) should equal or approach 1. For tungro disease counts, one study from Thailand revealed an R value of 0.1407 and an upper (95%) confidence interval of 0.5501. Although this value is low, without more field counts from more sites, it is premature to ask if tungro disease counts are repeatable. Although no scientific measurement is expected to have perfect repeatability, this Thai study underscores the need for plant protection workers to conduct frequent repeatability trials of their scientific measurements as a routine quality assurance procedure, particularly when multiple persons are required at multiple sites and when data from such studies are pooled for later statistical analysis. Surveillance scheme for tungro forecasting in Malaysia A.B. Othman, M.J. Azizah, A.T. Jatil Rice tungro disease in Malaysia was suspected to occur first in 1933. Serious outbreaks occurred in 1982 and 1983, when more than 20,365 and 12,439 ha, respectively, were affected. A nationwide campaign was launched to control the disease and to strengthen the rice pest surveillance and forecasting system. The techniques used were mapping, field surveillance, mobile nurseries, tests for viruliferous insects, and light traps. As a result of this campaign and the intensification of surveillance activities, the area of tungro infestation was reduced greatly. Green leafhopper-resistant or moderately resistant varieties were widely recommended and adopted. Surveillance for tungro was further refined by incorporating new components such as recording the severity of infestation, using a serological test (ELISA) to detect infection, and using ultraviolet light traps for monitoring GLH abundance and species composition. Economic threshold levels were established for decision making. Other information on natural control, natural enemies, farmers' attitudes and experiences, and availability of pest control equipment was also compiled. Farmers' rice tungro management practices in India and the Philippines H. Warburton, S. Villareal, and P. Subramanian Rice tungro disease is a serious disease for farmers because it is difficult to forecast and control, and can cause high yield losses. In this study, we compared the perceptions and practices of rice farmers in India and the Philippines, two areas where tungro is reported as endemic. The aim was to find out what farmers knew about tungro and how they coped with it. We also investigated the factors that influenced their knowledge and management practices. Community-based rice pest management X.H. Truong, E.H. Batay-an, S.C. Mancao, G.N.A. Abrigo, A.B. Estoy, L.B. Flor, Jr., H.D. Justo, Jr., E.R. Tiongco, R.N. Casco, and S.R. Obien An exploratory interdisciplinary approach with farmers' participation gave an expected and much-needed boost to community efforts to manage pest problems in three villages in Midsayap, North Cotabato. This simple intervention could slowly halt emerging pests to the area. A strategic action plan prepared after informal group dialogue was designed for farmers to help them understand the rationale of the project, learn from their farming experiences from the crisis due to damage caused by rice black bug (RBB) and rice tungro disease (RTD) in 1996, and alleviate fears of threats to their income, while sustaining their rice production. The plan encouraged farmers to participate in establishing their crop simultaneously with their neighbors, choose suitable varieties and crop establishment methods, and monitor pests prior to taking appropriate management action. The community shared ideas and experiences on crop management through a consultative and planning workshop, demonstration, experiments, and a farmers' field day. Based on the participatory rural appraisal method, their indigenous knowledge of farming, pest and control practices, financial constraints, and the irrigation schedule was used to establish an action plan. A total of 140 farmers in Bual Norte, Bual Sur, and Bobonao villages in Midsayap, North Cotabato, participated in the project for two to four cropping seasons in 1996-98. Most farmers (82-97%) realized that the intensive use of insecticides could not control the major pest problems of RBB, RTD, and white stem borer (WSB) in the staggered planting system. They changed gradually from staggered to synchronous planting with a 45-56-d and 30-45-d fallow period in each village. They shifted from transplanting to the broadcast method of planting (76-82%) and selected early maturing varieties (65-79%) and recommended varieties (20-35%). With this practice, farmers in these communities obtained an average rice yield of 3.2-4.6 t ha-1 and reduced RBB density (1.3-2.0 hill-1), RTD-infected farms (2.2-11.5%), and whitehead incidence caused by WSB (3-22%). They reduced the frequency of insecticide application from 5-6 times to 3-3.4 times per season. In general, farmers' perceptions and experiences influence their cultural management and pest control practices, which are also closely related to their sociodemographic characteristics. Thus, most farmers continued searching for varieties resistant to pests through seed exchanges with their friends. A few farmers still used insecticides intensively, especially those with an average income level. Some were aware of the presence of spiders and parasitized egg masses of WSB through information they received, but most farmers have not translated their ideas into farming practices. The results clearly suggest that the project's strategic action plan in the future should focus on the needs of specific target farmer groups. T.C.B. Chancellor, E.R. Tiongco, J. Holt, S. Villareal, and P.S. Teng Rice tungro disease is endemic in some intensively cultivated areas in the Philippines where planting dates are highly asynchronous. Results from a survey conducted in Albay Province in 1992-94 showed that tungro disease incidence was significantly lower on rice varieties that are resistant to the main leafhopper vector of tungro, Nephotettix virescens, than on susceptible varieties. Late-planted rice crops in both the wet and dry seasons had the highest incidence of tungro. In on-farm trials in North Cotabato Province, a virus-resistant advanced breeding line, IR68705-1-1-3-2-1, showed strong resistance to tungro. These findings are discussed in relation to developing optimal tungro management strategies for endemic areas. Improving IPM technology for rice tungro disease in Indonesia A. Hasanuddin, I.N. Widiarta, and Yulianto Rice tungro disease (RTD) is of great economic importance in Indonesia. RTD distribution is still expanding and the disease causes serious outbreaks in some seasons. In the 1994-95 wet season, RTD severely attacked rice plants in East Java and in the Surakarta region of Central Java. The yield loss was estimated to be approximately 25 billion Indonesian rupiah. RTD is successfully controlled in South Sulawesi by integrated pest management (IPM), combining planting at the appropriate time and the use of green leafhopper-resistant varieties in rotation. This control method needs to be adapted, however, before it can be applied elsewhere, especially in areas planted asynchronously. Some experimental activities have been carried out to improve IPM for tungro such as determining the minimum area necessary to conduct synchronized planting, adjusting planting time, adapting Nephotettix virescens to resistant varieties as the basis of variety rotation, and using selective weed sanitation to reduce infection sources. Experimental results indicated that tungro disease spread from a single source of diseased plants reached 200 m. In asynchronously planted fields, RTD incidence at harvest in an observed field correlated positively with RTD incidence at 6-10 wk after transplanting (WAT) in an area within a radius of 101-250 m when rice plants in the observed field were at 3 WAT. RTD incidence was high regardless of planting time in asynchronously planted fields. In synchronously planted fields, however, the later the planting time, the greater the disease incidence. RTD incidence in Bali, West Java, and Central Java was high on Cisadane and IR64, which possess the Glh5 resistance gene. N. virescens colonies collected from West Java, Central Java, Bali, and South Sulawesi were well adapted to IR64. Transmission of rice tungro viruses was achieved in six weed species. This information can be used to improve IPM for RTD in Indonesia. Leafhopper control by insecticides is not the solution to the tungro problem S. Villareal Green leafhoppers (GLH) are one of the most abundant canopy arthropods in irrigated rice systems throughout much of South and Southeast Asia. Populations are rarely large enough to cause direct feeding damage to rice, but in some areas they are important pests as vectors of rice tungro disease. In some countries in Asia, chemical control of GLH based on threshold numbers of the insect is still recommended. In the majority of rice-growing areas, however, tungro disease is absent or occurs infrequently. Consequently, routine insecticide applications against GLH cannot be justified. Moreover, spraying insecticides to control GLH does not always result in effective tungro disease management. Insecticides may be harmful to human health and to the environment and indiscriminate use of certain compounds in rice has been shown to cause outbreaks of secondary pests. Alternative methods of managing tungro disease in endemic areas are available and these should be used for GLH control. Currently, virus-resistant varieties are being developed and it is hoped that they will soon be available to rice farmers and that these varieties will provide them with a further option for managing tungro. The role of vector control in rice tungro disease management N. Widiarta Tungro disease, which is spread by rice green leafhoppers, especially Nephotettix virescens, is one of the most destructive diseases of rice. The disease is successfully suppressed by planting rice at the recommended time to avoid high disease pressure and by rotating varieties with resistance to green leafhopper in synchronously planted areas, for example, in South Sulawesi. Simultaneous planting, however, is difficult to practice by farmers for various reasons. Therefore, until recently, tungro disease expansion and outbreaks have mainly occurred in asynchronously planted areas, primarily in Bali and Java. The population density of green leafhoppers in paddy fields in those areas is maintained at a low level by the dispersal activity of adults. Integrated pest management (IPM) strategies have been developed based on characteristic population dynamics of the vector to reduce the proportion of viruliferous vectors. In this study, the use of antifeedants against N. virescens to control tungro spread in synchronously and asynchronously planted fields was also examined. The antifeedant and virus transmission inhibition activities of andrographolide, a major compound of Andrographis paniculata, and commercial insecticides such as imidacloprid, pymetrozin, MIPC, and nytenpyram were tested against female adults of N. virescens. Imidacloprid and nytenpyram showed better antifeedant activities than andrographolide and pymetrozin. Imidacloprid inhibited acquisition and inoculation of tungro viruses better than the others. The results imply that antifeedants have a potential to reduce virus transmission without directly disturbing the food chain. In asynchronously planted areas, application of diacloden and MIPC successfully decreased vector population density but not tungro spread. In synchronously planted areas, application of diacloden, imidacloprid, and MIPC significantly reduced both vector population density and disease incidence. GLH control for the management of rice tungro disease T. Ganapathy, N. Subramanian, and M. Surendran Green leafhopper (GLH) is one of the major sucking pests of rice and is capable of transmitting rice tungro disease (RTD), a devastating virus disease of rice. GLH is considered to be more important as a virus vector than as a direct pest of rice. In a seedbed protection trial, application of neem cake in the seedbed followed by spraying of 5% neem seed kernel extract (NSKE) at 30 d after transplanting reduced the incidence of tungro disease by more than 50% and increased rice grain yield. GLH abundance and the presence of a higher percentage of transmitters resulted in high RTD incidence. A significant positive linear relationship was observed between RTD incidence and both log transmitters and percent transmitter population during an RTD epidemic in the northern districts of Tamil Nadu, India, during 1991-93. Management of rice tungro disease by chemical control of the green leafhopper vector E.H. Batay-An and S.C. Mancao The field efficacy of five synthetic pyrethroid insecticides was evaluated for the control of green leafhoppers (GLH) and rice tungro disease (RTD) and for their effect on natural enemy populations and yield of IR64. In each of two seasons, pyrethroid-treated plots significantly reduced GLH populations and had significantly lower RTD incidence. Among the five treatments, plots treated with cypermethrin and ethofenprox had the lowest GLH population and RTD incidence at all sampling dates. Yields were higher in the treated plots than in the control. Populations of spiders, Cyrtorhinus lividipennis, Conocephalus longipennis, Agriocnemis pygmaea, and coccinellids were significantly affected by insecticide applications 1 d after treatment at 5, 20, and 35 d after transplanting (DAT). Cypermethrin, however, did not affect C. lividipennis populations at 20 DAT. Likewise, none of the insecticides reduced A. pygmaea populations at 35 DAT in the 1989 wet season or populations of any of the natural enemies at 35 DAT in the 1990 dry season. Sprays of cypermethrin and ethofenprox did not significantly affect the population of spiders, C. lividipennis, and A. pygmaea at 20 DAT in the 1990 dry season. |
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Rice tungro disease in the Philippines Preliminary analysis of genetic variation of rice tungro spherical virus in the Philippines Breeding for rice tungro disease resistance at PhilRice Breeding for rice tungro virus resistance in Indonesia Genetic engineering of rice for tungro resistance Are tungro disease counts repeatable? Surveillance scheme for tungro forecasting in Malaysia Farmers' rice tungro management practices in India and the Philippines Community-based rice pest management Improving IPM technology for rice tungro disease in Indonesia Leafhopper control by insecticides is not the solution to the tungro problem The role of vector control in rice tungro disease management GLH control for the management of rice tungro disease Management of rice tungro disease by chemical control of the green leafhopper vector |
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