Lysobacter enzymogenes strain C3 suppresses mycelium growth and spore germination of eight soybean fungal and oomycete pathogens and decreases disease incidences

Fungal and oomycete diseases can cause severe yield losses on soybean. Lysobacter enzymogenes strain C3 (LeC3) has been reported to be an effective biological control agent (BCA) against various plant pathogens. In the current study, we used a dual culture assay to test antagonism between LeC3 and eight fungal and oomycete pathogens of soybean, including Macrophomina phaseolina (causal agent of charcoal rot), Phytophthora sojae (causal agent of Phytophthora stem and root rot), Pythium spp. (causal agent of seedling blight), Rhizoctonia solani (causal agent of Rhizoctonia root rot), Sclerotinia sclerotiorum (causal agent of Sclerotinia stem rot), Cercospora sojina (causal agent of frogeye leaf spot), Fusarium virguliforme (causal agent of sudden death syndrome), and Septoria glycines (causal agent of Septoria brown spot). Our findings revealed that LeC3 was effective in suppressing mycelial growth or spore germination of all the soybean pathogens tested, which was bacterial dose- and medium nutrient-dependent. Microscopic examination indicated that LeC3 probably works by degrading cell structures. In greenhouse conditions, we observed that application of LeC3 by soil drench or seed treatment led to 16% to 27% increased biomass in co-inoculated plants as compared with F. virguliforme and R. solani-infected plants alone. In addition, spray application of LeC3 at 10⁷, 10⁸, and 10⁹ CFU/ml reduced lesions caused by S. sclerotiorum by 24, 38 and 86%, respectively. As a conclusion, these results suggest that LeC3 is a potential biological control agent with broad-spectrum antagonistic activities against fungal and oomycete pathogens of soybean.