Colony, morphological and biochemical characteristics of cotton phyllosphere bacteria and its antagonistic activity against the Alternaria leaf spot of cotton

Abstract

Cotton crop is known to suffer from number of fungal, bacterial and viral diseases. Among them, Alternaria leaf spot caused by Alternaria spp. is predominant in causing economic losses to the cotton crop in the country. Phyllosphere inhabitants termed as epiphytes may consists of a variety of bacteria and filamentous fungi. They also play a key role in carbon and nitrogen cycling and help in important environmental processes such as methanol degradation and nitrification. So, bacterial phyllosphere cultures (P1 to P8) were isolated from the Bt and non Bt cotton by leaf imprint method and dilution method. The colony characters of isolates of bacteria pertaining to their shape, size, elevation, margin, texture, appearance and pigmentation were recorded. Gram’s staining and endospore staining revealed that P1, P2, P3, P5, P8 were Gram positive, P1, P2, P5 were showing endospore staining and P1, P4, P6, P7 were rod shaped. Biochemical tests revealed that the eight isolates Bt and non Bt cotton were differed in each test and showed positive for the catalase and oxidase test. The isolates P1, P5 and P6 showed positive results to Voges proskauer test. Isolates P2, P4 and P6 revealed positive results of phyllosphere bacteria to Indole test. Whereas, isolates P1, P2 and P8 showed negative reaction to methyl red test. The phyllosphere bacterial isolates P3, P5 and P7 recorded negative reaction to gelatin liquefaction. Screening of phyllosphere microflora against Alternaria macrospora was conducted following dual culture technique for all the isolates. Phyllosphere bacterial isolate P5 recorded maximum growth inhibition with 57.41 per cent followed by P4 isolate with 53.52 per cent growth inhibition over the test fungus Alternaria macrospora. Whereas least per cent growth inhibition was reported in isolate P6 with 45.63 per cent.