Survey for Diseases and Evaluation of Cotton Germplasm Against Alternaria Leaf Spot

Survey conducted during kharif2012–13 in ten villages of Guntur district revealed the highest incidence of Alternaria leaf spot (30%) followed by Cercospora leaf spot (12%), Tobacco Streak Virus disease (9%) and bacterial blight (5%) in Lam village. Grey mildew and rust diseases were not recorded at flowering stage. Intensity of Alternaria leaf spot, bacterial blight, grey mildew, Cercospora leaf spot and rust was to the tune of 12%, 3.0%, 6.6%, 6.0% and 8.2% respectively. The species associated with Alternaria leaf spot was identified as Alternaria alternata based on conidial characters. Among twenty popular varieties and hybrids evaluated at Regional Agricultural Research Station, Lam, Tulasi 144 BGII and U5-SS-33 BGII showed resistant reaction while Jadoo and Brahma recorded moderately resistant reaction against Alternaria leaf spot; eleven varieties viz., L 799, L 788, L 761, L 755, L 804, L 1011, L 1008, L 604, L 801, L 763 and L 808 were moderately resistant. Two hybrids KSPL (KDCCH-065) and NCS 9605 and three varieties viz., L 765, L 389, L 762 were moderately susceptible. One hybrid (SWCH 4746 BG II) and one variety i.e. Narasimha (NA1325) recorded susceptible reaction to Alternaria leaf spot. In conclusion cotton farmers, may choose disease resistant hybrids as a component of integrated disease management to reduce cost of plant protection and thus reap maximum benefits.