Impact of Seed Applied Rhizobacterial Inoculants on Growth of Wheat (Triticum aestivum) and Cowpea [Vigna unguiculata] and their Influence on Rhizospheric Microbial Diversity

Current study was planned to demonstrate (Experiment I), the impact of seed bacterization (inoculation dose-10(6), 10(8), 10(10), 10(12) CFU/ml) with two bacterial isolates Variovorax paradoxus RAA3 and M11 (Unidentified) on growth and foliar nutrient content (NPK) of wheat (var. H1105 and PBW660) and cowpea (var. PL-1 and PL-2) cultivars under glass house conditions. Strain RAA3 treated plants exhibited most promising results for shoot fresh weight (26.7%, 30.2%), shoot dry weight (44.4%, 63.3%) and chlorophyll content (66.8%, 66.9%) as compared to the control plants of respective varieties. This inoculant also caused significant changes in the foliar nitrogen (14.5%, 14.2%), phosphorus (36.4%, 46.7%) and potassium (20.1%, 65.9%) content in wheat and cowpea, respectively, as compared to the non-inoculated plants. Moreover, the inoculum dose of 10(8) of bacterial inoculum was found to be most effective and thus, considered as an optimum dose for the plant growth promotion. In another study (Experiment II), seed bacterization with RAA3 (10(8) CFU/ml) on nine different varieties of wheat was performed, and significant varietal and treatment effect were observed for many of growth parameters as compared to untreated control plants. Overall results showed maximum response at inoculum dose of 10(8), therefore this dose was taken to assess the influence of PGPR inoculation on rhizospheric microbial diversity of wheat and cowpea. We observed that RAA3 inoculation has led to a shift in microbial population in both wheat and cowpea varieties. Irrespective of varieties, RAA3 (inoculum dose of 10(8) CFU/ml) treated plants of wheat showed dominant microbial groups of siderophores producers, nitrogen fixers and actinomycetes, whereas, in RAA3 treated plants of cowpea the dominant microbial population of only siderophores producers was recorded.

Automated summary

The study demonstrated the impact of seed bacterization with two bacterial isolates on growth and foliar nutrient content of wheat and cowpea cultivars, showing significant changes in plant growth and nutrient content. The inoculum dose of 10(8) was found to be most effective. Additionally, RAA3 inoculation led to a shift in microbial populations in both wheat and cowpea varieties, with different dominant microbial groups observed in treated plants.