Efficacy of plant growth promoting bacteria Bacillus amyloliquefaciens B9601-Y2 for biocontrol of southern corn leaf blight

Southern corn leaf blight caused by Bipolaris maydis is one of the major threat to maize production worldwide. In this study, Bacillus amyloliquefaciens B9601-Y2, previously isolated from wheat rhizosphere, exhibited antagonistic effect against several important phytopathogens, solubilized mineral phosphate, potassium and was able to grow without nitrogen under in in vitro conditions. To further evaluate its potential agricultural use, maize pot and field experiments were performed to evaluate the plant growth-promotion and southern leaf blight suppression of B9601-Y2 culture. The results showed that B9601-Y2 significantly promoted maize seedling growth, improved several enzymes associated with soil quality, as well as increased chlorophyll content. After challenge inoculation 10 days with Bipolaris maydis, the causal agent of southern leaf blight, B9601-Y2-treated maize plants showed 61.38% decrease in disease index. To determine the antagonistic mechanism of B9601-Y2, its colonization pattern in the rhizosphere and maize tissue were also investigated using a GFP marker. The results indicated that B9601-Y2 predominantly colonized the elongation zones of primary roots, root hairs and the junctions between roots, subsequently entering the stems and leaves. The population dynamics of GFP-tagged B9601-Y2 in the rhizosphere and on maize roots were monitored. B9601-Y2 significantly reduced southern leaf blight severity in maize and increased its marketable yield under field conditions. The present study demonstrated that B9601-Y2 may be developed as a promising biocontrol and plant-growth-promoting agent due to its enhanced nutrient solubilization and disease suppression traits.