Combined interaction between the diazotrophic Niallia circulans strain YRNF1 and arbuscular mycorrhizal fungi in promoting growth of eggplant and mitigating root rot stress caused by Rhizoctonia solani

Abstract

Rhizoctonia root rot of eggplant, caused by Rhizoctonia solani, is an economically important disease. Niallia circulans YRNF1 and arbuscular mycorrhizal fungi (AMF) were assessed for their biocontrol and biofertilizing effects against R. solani, as potential replacements for synthetic fungicides and fertilizers. The diazotrophic N. circulans YRNF1, isolated from soil, reduced in vitro growth of R. solani by 42%. GC-MS analysis of culture filtrate of N. circulans YRNF1 detected bioactive compounds, including butyric acid (85%) and ethylene glycol (8%). In greenhouse experiments, combined application of N. circulans YRNF1 and AMF reduced the severity of eggplant root rot by 26%. This combined treatment triggered the transcriptional expression of five resistance genes (JERF3, PAL1, C3H, CHI2, and HQT) in the treated eggplants. Biochemical analyses of the infected eggplant roots treated with the combined bio-inoculants showed enhancement of the phenol content (+188%), and increased antioxidant enzyme activity, mainly of POD (+104%) and PPO (+72%). Combined application of N. circulans YRNF1 and AMF also promoted eggplant growth and improved the total NPK concentrations in treated plant leaves. Inoculation of eggplant with N. circulans YRNF1 in the presence of AMR increased the mycorrhization level. This is the first report of N. circulans and AMF as potential agents for biological control of Rhizoctonia root rot and growth promotion of eggplant.