Biocontrol of Lysobacter enzymogenes CQ18 against the tobacco powdery mildew fugus, Erysiphe cichoracearum

Abstract

Background

Powdery mildew is a common leaf disease of crops worldwide. A large quantity of chemical fungicides is used to control this disease in horticulture and agriculture, producing serious safety and environmental problems. To suppress this disease in safe and environment-friendly ways, the biocontrol of a self-isolated new strain of Lysobacter enzymogenes (CQ18) was studied against flue-cured tobacco powdery mildews.

Results

L. enzymogenes CQ18 produced chitinase, protease, β-1,3-glucanase, phosphatase, and siderophore, which may enable this biocontrol bacterium to degrade pathogen cell membranes and walls and deprive pathogens of iron. HPLC/MS analysis identified 14 antifungal metabolites present in L. enzymogenes CQ18 fermentation liquid (LEFL), which were grouped into organic acids, azoles, and pyrimidines. The variable targets in or on pathogen cells and combinative effects of these multiple metabolites may potently suppress the powdery mildew and be less likely to make Erysiphe cichoracearum develop resistance. LEFL was rich in L-pyroglutamate. Both LEFL and L-pyroglutamate inhibited the germination of E. cichoracearum conidia in vitro and reduced the powdery mildew index in the greenhouse and field. L-Pyroglutamate at a concentration of 0.50% achieved the same control efficacy as the chemical fungicide triadimefon (91–94%).

Conclusions

L. enzymogenes CQ18 and the metabolite L-pyroglutamate effectively controlled flue-cured tobacco powdery mildew. L. enzymogenes CQ18 grows rapidly and is resilient to adversity. L-Pyroglutamate has no toxicity to humans and is easy to synthesize at a low cost. Both show potential use in controlling plant powdery mildews.

Graphical Abstract