Screening of potential bacterial isolates against Phytophthora capsici and its plant growth-promoting effect on pepper plants

Phytophthora blight, is the most devastating disease of pepper production. To increase agricultural yield and control diseases, many countries in the world use synthetic agrochemicals. However, it has negative effects on human health and the environment, but there are few reports on its biological control. Out of sixty bacterial strains, four that showed biocontrol and plant growth promotion, namely Enterobacter hormaechei , Rhizobium sp., Pseudomonas fluorescens , and undetermined (AAULE51), which were isolated and identified using biochemical tests and 16S RNA sequences. All bacterial strains that showed greater than 55.5% growth inhibition of Phy-tophthora capsici in dual culture were selected for greenhouse and field studies. Also, the antimicrobial activity of the cell-free filtrate of the strains were assessed. AAULE51 was found to be the best inhibitor against P. capsici, ranging from 90.34 to 100% at a concentration of 20%-75%. The effects of bacterial strains on seed germination, vigor index, seedling height, and fresh weight of pepper plants were measured in vitro and showed 70-90.6%, 1069.6-2650%, 37-48 mm, and 64-70 mg, respectively. In greenhouse and field studies the biocontrol efficacy of antagonistic bacteria against P.capsici ranged from 0.6% to 94.2%, and 11%-84.6% respectively. The maximum reduction in disease severity was shown when treated with AAULE41+ AAULE51 (61.1%-94.2%). Therefore, these results suggest that selected potential bacterial strains are good candidates for agricultural biofertilizers and biopesticides.