Characterization of faba bean (Vicia faba L.) rhizosphere associating rhizobacteria against Botrytis fabae AAUBF-12 and their plant growth-promoting properties

The rhizobacteria are known to protect plants from different pathogens acting as biocontrol agents and promote growth of plants. This study was conducted to isolate, screen and identify faba bean associating rhizobacteria for their antagonistic properties against Botrytis fabae AAUBF-12 and plant growth-promoting properties under in vitro conditions. In the dual culture assay, the isolates inhibited the mycelia growth of B. fabae AAUBF-12 (6–40 %) upon 3 days of incubation, and the inhibition increased to 9–43 %, 16–50 %, and 24–68 % after five, seven and 9 days of incubation, respectively. The inhibitory activity increased from 6 to 82 % using the culture filtrates of the isolates. Isolate AAUB95 displayed the highest mycelial inhibition (27 %) at 5 % concentration of culture filtrate, followed by AAUB146b that exhibited 21 % inhibition at the same concentration. AAUB146b and AAUB100 effectively inhibited B. fabae AAUBF-12 by 79 % and 80 % at 20 % concentrations of the culture filtrate. The qualitative study demonstrated 75 % of the isolates positive for protease and 60 % for lipase synthesis. Furthermore, the isolates that showed antagonistic activity against B. fabae AAUBF-12, produced IAA and ammonia with 65 % and 60 %, respectively. Moreover, 310–760 μg mL(−1) and 200–620 μg mL(−1) of tricalcium phosphate (TCP) was released on the 3(rd) and 6(th) days of incubation, respectively, due to rhizobacterial solubilization. Nevertheless, the Pearson's correlation analysis between pH and TCP solubilization revealed an inverse relationship (r = -.422∗∗). Based on 16S rRNA sequences analysis, isolate AAUB95, AAUB146b, AAUB100 and AAUB92 were identified as B. subtilis AAUB95, S. nematodiphila AAUB146b, B. tequilensis AAUB100 and B. subtilis AAUB92, respectively. Of the isolates, B. subtilis AAUB95 showed best antagonism of B. fabae AAUBF-12 with multiple plant growth-promoting properties.