Biological control of sclerotial blight of tea using arbuscular mycorrhizal fungus and plant growth promoting rhizobacterium.

Glomus fasciculatum , one of the dominant arbuscular mycorrhizal fungus (AMF) associated with tea root colonization, was selected and maintained in maize plants. Besides AMF, Bacillus amyloliquefaciens TRS6 isolated from tea rhizosphere, which showed in vitro antagonism to a number of tea root rot pathogens as well as siderophore-producing and phosphate-solubilizing activities, was selected for utilization as bioinoculants in tea plants for improvement of health status. The bacterium was applied to the soil as aqueous suspensions, and in case of G. fasciculatum , soil was inoculated with its spores and in joint inoculations, the AMF was inoculated prior to the bacterium. Inoculation of rhizosphere of tea plants of six different varieties (TV-18, T-17, AV-2, T-78, UP-3 and UP-26) with any of two microorganisms increased growth of plants, but the most significant increase was obtained in dual application. Plant growth was measured in terms of increase in height, increase in number of branches and leaves. Similarly, sclerotial blight of tea, caused by Sclerotium rolfsu , was suppressed to certain extent by G. fasciculatum or B. amyloliquefaciens , but significant suppression occurred when G. fasciculatum and B. amyloliquefaciens were applied jointly. Polyphenolics and four major defense enzymes showed enhanced activities during disease suppression. Western blot of the enzjone extracts from control and all treated plants using PAb raised against chitinase revealed strong reaction when disease suppression was evident. Population of S. rolfsu in soil was also determined following immunological techniques using PAb raised against the pathogen. Results of ELISA and dot-blot revealed that application of G. fasciculatum and B. amyloliquefaciens significantly reduced S. rolfsu population.