Seed Priming with Sulfur Oxidizing Bacteria Isolated from the Rhizosphere and their Effect on Vigna radita (L.)

The plant rhizosphere harbors various kinds of microbes that play significant roles in plant growth. Sulfur oxidizing bacteria (SOB) play a vital role in the oxidation of elemental sulfur to plant accessible sulfate, which helps in plant growth, acts as a biocontrol, and acts as a bioleaching agent. In our present work, we explored the diversity of sulfur oxidizing bacteria from the rhizosphere of Catharanthus, Begonia, Pisum, Trigonella, Spinacia and Azadirachta. Twenty five bacterial strains were isolated and stabbed in thiosulfate containing growth medium. Out of twenty five isolates, six most effective strains, CR1, PS2, SO3, TF4, BS5 and AI6 with a remarkable change in color of the thiosulfate containing growth medium from red to yellow due to sulfate production, were selected for plant growth promoting activities such as phosphate solubilization, IAA production, HCN and ammonia production. All six bacterial strains showed significant Plant Growth Promoting Rhizobial (PGPR) activities with the production of indole-3-acetic acid (662 to 724 μg ml^-1) and phosphate solubilization (7 to 14 μg ml^-1). Selected strains and their consortium are further assessed for growth responses on Vigna radiata L. under in-vitro conditions. Based on the analysis of variances, seed priming with different sulfur oxidizing bacterial strains showed a significant (P < 0.05) effect on vigor index. The vigor index increased in primed as compared to unprimed seeds of Vigna radiata L. The maximum growth rate of seedlings for the single culture of CR1 (10.80) and for the mixed culture of CR1 + BS5 (10.94) was observed as compared to the control. All six SOB strains showed in-vitro plant growth promoting activities and may be used as a viable alternative to organic fertilizers and as potential applicants for sustainable agriculture.