Assessment of severity of important diseases of rainfed Bt transgenic cotton in Southern Maharashtra

In recent days, cotton cultivation in India has witnessed some of the most pronounced changes in cultivars, agronomic and protection practices. There has been a gradual shift from conventional cultivation of G. arboreum, the short staple cultivars to transgenic cotton. The crop confined earlier to dry land is now cultivated with high inputs and heavy schedules of plant protection. The significant relief in level of bollworms infestation by synthetic pyrethroids and other chemicals revolutionized the cotton crop protection technology followed by genetically modified crops. These alterations have brought in many new biotic problems like parawilt and foliar diseases nither to less economic importance. Between 1978 and 1989 the parawilt has been reported mainly from central and southern cotton growing areas of the country (10). In Maharashtra, the sporadic incidence noted on cv. DCH-32 during 1982 (7) became a serious concern with large scale cultivation of hybrids (NHH 44, MECH 1, JKHY 1, PH 36, and AHH 468). Roving surveys of late 1990s revealed that the disease was well distributed. The most significant effect of parawilt was on staple length, fineness, bundle strength, ginning output, seed weight, maturity coefficient, germinability, and vigor index (8,10,11). Transgenic Bt cotton was approved for commercialization by Government of India in 2002 and about 40,000 ha has subsequently gone under three Bt cotton hybrids in central and south zones. In order to develop IPM technology, large-scale field validation trials involving 2 transgenic Bt cotton hybrids (MECH 162 and 184) were conducted in village Naigaon situated 60 km away from Nanded (MS) during 2002-03 and 2003-04 crop seasons. Studies were designed to generate data on disease situation on Bt transgenic cotton vis-a-vis conventional cotton.