Ufra - The Deeply Mysterious Disease

Abstract

Deep-water rice/floating rice/long-stemmed rice/bao dhan is the only crop that provides a means to use the unruly flood water to the advantage of human beings in many parts of Asian and West African countries. The production of this long duration crop (150‒240 days) is severely affected by several abiotic and biotic stresses. Ditylenchus angustus, commonly known as rice stem nematode or ufra nematode, is considered as one of the major constraints for successful production and productivity in Southeast Asian countries, being responsible for 10‒90 per cent yield loss. In severe conditions, farmers fail to harvest a single panicle. This stubble-borne, obligate parasite of rice, capable of infesting 13 different species of Oryza and a few weed species, is distributed throughout the deep-water growing countries of the world. The symptoms of the disease caused by this nematode (ufra disease) are not recognizable at the early stage of crop growth, though infested crops develop disease symptoms like white patches, or dot and/or dashes at the base of the leaf in a splash pattern or mosaic-like discolouration and shows leaf chlorosis or white coloured streaks on young leaves and sheaths etc. at about two months of crop growth. The most typical and conspicuous symptoms of the ufra disease are seen at the heading stage of the crop. Based on the degree and time of infestation, the ufra symptoms may be classified as ‘thor ufra’ or swollen ufra and ‘pucca ufra’ or ripe ufra; or may be reclassified as ‘ufra-I’, ‘ufra-II’ and ‘ufra-III’. Humidity, temperature, rainfall, and water depth are major abiotic factors in disease development. The disease may be controlled to a greater extent by burning of diseased stubbles before sowing the seeds, delayed sowing, transplanting deep water rice wherever possible, crop rotation with mustard and jute, crop diversification, use of resistant varieties, application of balanced fertilizers with zinc. Soil application of granular nematicides before sowing the rice seeds is also effective in managing this disease.