Screening of sunflower associated bacteria as biocontrol agents for plant growth promotion.

Deleterious effects of artificially applied chemicals have highlighted the significance of biocontrol agents as suitable substitute for sustainable agriculture. In present study, three endophytic bacterial strains SV7, SV10 and LV19 showed extensive range of antifungal as well as plant growth promoting activities signifying potential to accomplish the requirement. Phylogenetic analysis revealed 100% similarity of three strains with taxon Firmicute. However, there was division among these isolates on basis of subgroups as SV7 belonged to Exiguobacterium auranticum, SV10 belonged to Paenibacillus sp. and LV19 was best fit in subgroup Priestia koreensis. All strains showed antifungal activity against Fusarium oxysporum on three different media (PDA, NA, LA) with maximum activity (53%) of LV19 strain on NA and least activity (13%) on PDA medium as recorded by zones of inhibition. In growth promotion experiments, combination of LV19 with Fusarium significantly suppressed chances of Fusarium wilt which is commonly caused by Fusarium oxysporum in sunflower plants. Diverse growth parameters (seed germination percentage, lengths and fresh weights of root and shoot) were significantly increased from 34 to 909% over pathogen infected plants only which was further proved by their root colonization analysis. Based on most efficient growth promotion by LV19 strain, expression of five plant defense related genes (SOD, PAL, NPR1, PR5, Chitinase) was evaluated revealing enhanced expression by 1.7-270-folds in consortium of LV19 and Fusarium. Thus, current study provided a scientific justification that bacterial strains in specific LV19 (Priestia koreensis) could be further developed as biocontrol agent with potential of plant growth promotion.