Field evaluation of bt and non bt cotton hybrids to foliar diseases

Identification of resistant sources is a prerequisite for management of diseases through the use of resistant varieties/hybrids that constitutes an important strategy of integrated plant protection. Ninety two Bt and five Non Bt cotton hybrids were evaluated at Regional Agricultural Research Station, Guntur using infector row technique under unprotected conditions. Reaction of these hybrids to bacterial blight and fungal foliar diseases was recorded by adopting 0 to 4scale and percent disease intensity was calculated. Four entries viz., RCH-368 Bt, Brahma BG-I, MRC-7347 BG-II and MRC-6918 Bt recorded moderately susceptible reaction to bacterial blight; RCH-530 BG-II was resistant and 38 were moderately resistant to Helminthosporium leaf spot; 28 hybrids showed moderately resistant reaction to Myrothecium leaf spot; Tulasi-118 BG-II was free from Cercospora leaf spot while seven hybrids viz., ABCH-1020 Bt, GK-207 Bt, RCH-368 Bt, Dhruv Bt, ACH-33-1 Bt, NCS-854 BG-II and NHH-44 Bt recorded resistant reaction. Six hybrids viz., MRC-7347 BG-II, PRCH-505 BG-II, NCS-854 BG-II, GK-217 BG-II, ACH-6 BG-II and VBCH-1506 BG-II were free from rust while Tulasi-118 BG-II, MRC-7351 BG-II, ACH-5 BG-II, ACH-111 BG-II, MRC-7201 BG-II and NCEH-2R F Bt were resistant. MRC-7347, Brahma BG I, RCH-368 Bt, RCH-530 BG II, Tulasi-118 BG II and MRC-6918 showed multiple disease resistance/tolerance. Cotton farmers should grow best Bt cotton hybrids with multiple disease resistance/tolerance to reduce the cost of plant protection and increase net returns.