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A total of 26 endophytic Methylobacterium sp. strains were obtained from surface sterilized leaves of two banana cultivar (Robusta and Nattu poovan) and the strains were tested for its ability to fix atmospheric nitrogen, EPS and IAA production for promoting banana tree growth. The result of the present study demonstrated that endophytic population ranged from 4.03 and 4.14 log cfu per gram of leaf tissue. Among these four isolates were chosen based on colony morphology and their distinct pigmentation. All the selected four isolates were able to grow in nitrogen free methanol mineral salt medium. The synthesis of indole-3-acetic acid (IAA) in the presence of L-tryptophan was detected in all the isolates tested. The isolate FM2 (Methylobacterium sp.) produced the highest amount of IAA (13.01g ml-1) in medium supplemented with L-tryptophan and was able to synthesize IAA in the absence of L-tryptophan. The maximum amount of ASP and WSP was recorded in FM3 (21.73 µg ml-1) and FM1 (157.79 µg ml-1), respectively. They were tentatively identified at species level based on carbon utilization test. The classified strains were also screened for methanol dehydrogenase (mxaF gene sequencing) using specific primers and obtained 555 bp PCR product. So the Methylobacterium sp. strains analyzed here had a promising potential for developing as a plant growth promoting bacteria for sustainable agriculture.

Abstract:In the context of increasing international concern for food security and environmental quality, the use of bioinoculants like diazotrophs and plant growth-promoting rhizobacteria (PGPR) for reducing chemical inputs in agriculture is a potentially important issue. The improvement in agricultural sustainability requires optimal use and management of soil fertility and soil physical properties, where both rely on soil biological processes and soil biodiversity. Biological nitrogen fixation by plant-associated bacteria is eco-friendly and has been effectively exploited for crop plants including legumes. Although associations of rhizobacteria with non-leguminous plants such as grasses have been known for decades, they have been poorly -studied. Weedy grass species normally thrive in adverse conditions and act as potential habitats for the diverse groups of elite bacteria with multiple beneficial characters remains unexplored. A more complete understanding of the diversity and functioning of rhizobacterial microorganisms, especially those that have symbiotic relationships with grass species is of great value for agricultural research and application.