Isolation and characterization of endophytic bacteria with plant growth promoting traits from maize (Zea mays)

Endophytic microbes that colonize the inner tissues of plants without causing any disease or damage play an important role in the growth and development of host plants that grow under both normal and stressful conditions. Plant growth-stimulating effect of endophytes is manifested by coordinated action on phytohormone production, biological nitrogen fixation, phosphate solubilization, modulation of 1-aminocyclopropane-1-carboxylic acid deaminase (ACC) expression and siderophore production. In this study, 106 endophytic bacterial strains were isolated from leaves, stems, roots and kernels of maize plants collected from different regions of Andhra Pradesh. The ability of these strains were evaluated for plant growth promoting activities. Out of 36 effective isolates, 15 strains were found to grow on N-free semisolid media supplemented with bromothymol blue (BTB) indicator, showed solubilization index varying from 4-6 on Pikovskayas agar, potassium solubilizing index from 1.2-2.5 on Alexandrov agar. Majority of the isolates were found to be positive for IAA production, siderophore production, HCN production and growth on ACC supplemented DF (Dworkin and Foster) minimal agar indicating ACC deaminase activity. The multi trait plant growth promoting isolates can be used microbial inoculants after being tested for growth promotion in maize under field conditions.