Antifungal activity and control efficiency of endophytic Bacillus velezensis ZJ1 strain and its volatile compounds against Alternaria solani and Botrytis cinerea

Tomato early blight and grey mould are common diseases that affect tomato yield and quality. Endophytic bacteria are a class of biocontrol microorganisms that exist widely in plants that can, along with their metabolites, be used to develop new bacterial agents to control plant diseases and regulate plant growth while reducing the need for chemical pesticides. We previously isolated an endophytic bacterium ZJ1, Bacillus velezensis, from the stem of Buddleja lindleyana. The volatile organic compounds (VOCs) from ZJ1 exhibited significant antifungal activity against Alternaria solani and Botrytis cinerea. The VOCs were identified via gas chromatography–mass spectrometry of solid-phase microextraction samples (SPME–GC–MS). The results revealed eight main VOCs released by the strain ZJ1, among which isooctanol and 2-nonanol showed inhibitory effects on the mycelia growth of A. solani and B. cinerea. Furthermore, 2-nonanol and isooctanol showed good in vitro antifungal activity and in vivo control effect against the two pathogens. The 500 million CFU mL−1 ZJ1 strain oil suspension with 200 times dilution had the highest control effect, the protective and therapeutic effects were both greater than 80%. Additionally, treatment with ZJ1 and its VOCs caused the mycelium of A. solani to become thin, twisted, deformed, bifurcated, and fractured, with a wrinkled and cracked surface. The VOCs caused leakage of the mycelia intracellular contents, thereby causing withering. Collectively, these findings suggest that the preparation of the ZJ1 strain and its VOC products, 2-nonanol and isooctanol, has good application prospects for the control of tomato early blight and grey mould.