Synergistic inoculation of Azotobacter vinelandii and Serendipita indica augmented rice growth

In the rhizosphere, microbes act as crucial constituent for plant growth and development. The root-endophytic plant growth-promoting fungus-Serendipita indica and nitrogen fixing bacterium Azotobacter vinelandii are well known for plant growth promotion and stress alleviation. Individual inoculation of S. indica or A. vinelandii strain SRIAz3 has already been reported to augment plant growth. Therefore, it would be interesting to investigate the mutual interaction among these two microbes along with their symbiotic influence on growth of rice plant. The present study explores the interaction of S. indica and A. vinelandii strain SRIAz3 under in vitro condition and perceive their cumulative effect on rice growth. Differential growth response of S. indica was observed after inoculation of A. vinelandii strain SRIAz3 on different days. An enhanced S. indica growth in terms of hyphal radius and dry cell weight was found when SRIAz3 was inoculated 7 days after fungal inoculation. Moreover, confocal microscopy analysis revealed that A. vinelandii strain SRIAz3 cell-free supernatant increased S. indica spore germination. The sequential inoculation of A. vinelandii strain SRIAz3 on seventh day after S. indica inoculation in rice variety IR64 demonstrates better growth in terms of root-shoot biomass and chlorophyll content as compared to the non-inoculated and to singly inoculated plants. These findings recommend the sequential inoculation of S. indica followed by A. vinelandii strain SRIAz3 for the enhancement of rice growth.