Development of plant growth promoting microbial consortia based on interaction studies to reduce sclerotinia rot in brassica oleracea L

Abstract

In this study an attempt was made to isolate and formulate a bacterial consortia which could act as a Plant Growth Promoting Rhizobacteria (PGPR) with broad spectrum antagonistic potential against phytopathogens especially against Sclerotinia rot caused by Sclerotinia sclerotiorum L. From 6 rhizospheric soil, 10 Pseudomonas sp. and 13 Bacillus sp. were isolated and their antagonistic activity was tested on 6 fungal phytopathogens which were known to cause damping off diseases in plants. Nine of the above isolates exhibited varied percentage of antagonistic activity along with PGPR attributes like PO4 solubilisation, production of siderophore, IAA, HCN ammonia, etc., Through inters train interaction studies isolates B12, B20, P22 and B23 were found to be compatible with each other and were used for further experiments. Consortia B12+B20+P22 and B20+P22+B23 showed increased seed germination potential on cabbage and cauliflower seeds respectively. Interaction studies of the bacterial isolates using spectrophotometric method proved that neither the cells nor their extra cellular products inhibited each other. Partially amplified 16S rDNA sequences of the isolates gave their molecular identity. B12 was identified as Bacillus subtilis (GenBank Acc. No. MG586233.1), B20 as Bacillus subtilis strain J20A (GenBank Acc. No. MG601747.1), B23 as Bacillus subtilis strain J20B (GenBank Acc. No. MG602478.1) and P22 as Pseudomonas aeruginosa strain J22P (GenBank Acc. No. MG738317.1). Bioformulation and shelf life studies were done using four different carriers (talc, lignite, saw dust and peat) supplemented with CMC as a binding agent. The survival percentage of the bacterial consortia in lignite was found to be the best in RT and at 4°C. In the disease control study using cabbage as the experimental plant, challenged inoculated plants (T4) gave efficient protection in host plants due to which till 60th day, infection (lesions) was not spotted in plants. 90th day onwards the plants showed characteristic lesions on leaves but the plants were healthy with the formation of juvenile heads indicating the efficient protection exerted by the bacterial biocontrol agent (consortia) against S. sclerotiarum. There was an increased production of plant defence inducing substances in the infected (T3) and challenged inoculated (T4) plants. This suggests that the presence of PGPR could trigger Induced Systemic Resistance (ISR) in the host plants thereby protecting plants against the infections. These results suggests that the bacterial consortia composed of Bacillus subtilis and Pseudomonas aeruginosa could be used control Sclerotinia rot in cabbage along with plant growth promotion. newline