Volatile organic compounds of L. enzymogenes LEC suppress the growth of fungal and oomycete pathogens and modify the cell physiology of Rhizoctonia solani

Lysobacter enzymogenes LEC is a plant disease-suppressive bacterium. To obtain a more comprehensive understanding of its biocontrol activity and to identify further potential application methods, we investigated the function of its volatile organic compounds (VOCs). VOC activity was assessed in vitro using split-plate assays with eight different fungal and oomycete isolates and in planta against Pseudoperonospora cubensis on cucumber plants. The volatilomes of LEC and the less active L. enzymogenes DSM2043 were analysed by GC-MS analyses. Further, the effects of VOCs on cell physiology of Rhizoctonia solani were analyzed by fluorescence and transmission electron microscopy. The strongest inhibition of LEC VOCs was observed for Phytophthora infestans (94%) and Phoma lingam (83%), while inhibitions were lower for Rhizoctonia solani (42%) and Alternaria spp. (24% and 29%) and not detectable for two Fusarium isolates. VOC exposure also significantly reduced downy mildew caused by P. cubensis on cucumber plants (39%), although this effect was locally restricted to the leaf directly above the VOC source. In R. solani, VOC exposure reduced nuclei abundance and increased lipid accumulation. GC MS analyses revealed distinct volatile profiles between LEC and L. enzymogenes DSM2043 and identified ketones, such as 2-dodecanone and undecanone as candidate bioactive compounds, which is in agreement with previous findings. Our results demonstrate broad-spectrum VOC-mediated biocontrol activity, and thereby provide a more comprehensive understanding of its biocontrol activity and highlight new ways for potential applications of LEC.