Current Status and Future Prospects of Research on Bacterial Blight of Rice

New diseases arise when agriculture moves toward higher productivity. With a change of rice ecology, some formerly less important pests emerge, others vanish, and new ones appear. Bacterial blight is not a new disease of rice. Its importance to rice production in tropical Asia, however, was recognized only after the introduction of modern cultivars, which are highly responsive to nitrogen fertilizer. It is now a major rice disease throughout Asia. Bacterial blight is especially prevalent in irrigated and rainfed lowland rice areas in Asia. Severly infected leaves tend to dry quickly, and many farmers attribute the effects of the disease to drought, thus letting it go unnoticed. In the last twenty years, epidemics have been reported prior to the introduction of modern rices. Since the introduction and widespread cultivation of high­ yielding but susceptible rice cultivars, bacterial blight has become one of the most serious diseases of rice in Asia. In Punjab, Haryana, and western Uttar Pradesh States of India, major epidemics occurred in 1979 and 1980 ( 14); severe kresek was observed; and total crop failure was reported. Estimates of yield losses caused by bacterial blight are not available. The extent of yield loss depends on locality, season, weather, and cultivar. An increase in the amount of nitrogen fertilizer application favors disease development and thus causes greater yield loss (60) . The amount of nitrogen applied did not increase the incidence and severity of the disease in a resistant cultivar. In recent years the disease has been observed not only in all major rice­ producing countries of Asia, but also in the Sahelian countries of Africa (1)