Epidemiology and Management of Leaf Spot of Cotton Caused by Alternaria spp

Abstract

Cotton, does not need much emphasis as being the principal raw material for a newlineflourishing textile industry. The research studies revealed that the maximum Alternaria leaf newlinespot disease severity was recorded in Gulbarga, Yadagiri, Dharwad and Raichur districts. newlineAmong 17 isolates, in morphological studies mean colony diameter ranged between 60 mm newline(Hirebagevadi) to 84 mm (Bagalkot). The mycelial width was larger in Kalmala (4.76 and#956;m) and newlinewas least in Hattigudoor (2.53 and#956;m). The dimensions of conidia of Kalmala isolate showed newlinemaximum size of 43.98-76.89 x 8.43-18.70 and#956;m and Annigeri isolate showed maximum beak newlinelength of 16.30 and#956;m. newlineThe temperature studies revealed that, the Hanumanamatti isolate (230.20 mg) newlinerecorded maximum dry mycelial weight. The highest dry mycelial weight was recorded at newline30oC (252.38 mg) followed by 25oC (237.76 mg). The dry mycelial weight was significantly newlinesuperior at pH 7 (230.21 mg), followed by pH 8 (215.18 mg). RAPD analysis revealed the newlinemaximum genetic similarity of 93 per cent between Gabbur (A7) and Sunkeshwarhal (A8) newlineisolates, whereas the least similarity (40 per cent) was between Hattigudoor (A9) and newlineYaragatti (A13). The isolates were made into i.e., A cluster and B cluster. newlineStepdown regression led to the equation as Y = 235.94 + 9.89X1 11.84X2 + newline1.89X3 + 0.64X4 1.23X6 with R2 value of 0.78 including variables maximum temperature, newlineminimum temperature, RH (morning), RH (evening) and rainy day. Fungi viz., Alternaria spp., newlineFusarium spp., Helminthosporium spp., Aspergillus spp., Penicillium spp., Rhizopus spp. and newlineMucor spp. were detected in infected seeds and survival studied for more than 14 months in newlinerefrigerator condition. newlineThe maximum per cent avoidable yield loss was recorded in Propiconazole (0.1%) at newline35, 55, 75, 95, and 115 DAS. Yield reduction was 32.38 per cent in Bunny Bt caused by newlineAlternaria leaf spot. Seed Treatment (ST) of Vitavax power (0.3%) + Foliar Spray (FS) with newlinePropiconazole (0.1%) significantly lowered Alternaria leaf spot per cent disease index. newlineHowever, the ST of Vi