Rice disease is one of the major barriers to high and sustainable rice productivity. Deploying resistant varieties is the most effective and economical way to control disease and it plays a key role in world rice productivity (Mew, 1991; Bonman, Khushand Nelson, 1992). During the 1970s and 1980s, when epidemics of rice tungro were frequent in the Philippines and Indonesia, farmers expressed more confidence in using resistant varieties than in other control measures. There are limitations, however, in using resistant varieties alone to manage rice disease. Most varieties are only resistant to a few major diseases that are the subject of intensive breeding efforts. Rice production environments, particularly in the tropics, provide the habitat for many rice pathogens causing varying degrees of damage. Even the "minor" diseases could collectively pose a significant threat to production (Mew, 1992a). Epidemic loss is dramatic but less frequent, whereas endemic loss is less obvious but pervasive in eachcropping season. Recent surveys indicated that an estimated annual yield loss of between 1 and 10 percent was due to a combination of different diseases (Savary et al., 2000a). Thus, resistance against a few targeted diseases only offers a partial solution to rice disease problems. To those diseases caused by non-specialized pathogens, such as sheath blight and false smut (caused by Ustilaginoidea virens), no useful source of resistance has been identified to improve the resistance of rice varieties. To achieve sustainability of rice production in Asia, what is needed is a rice production system built upon effective resistant varieties with broad resilience to a range of diseases and insect pests. Broad-spectrum resistance at the genotypic level and sustainability at the cropping systems level are therefore complementary approaches in the management of rice diseases.
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