Biological control of gray mold of tomato by Bacillus altitudinis B1-15

Gray mold, caused by Botrytis cinerea, is one of the most serious and widespread diseases that affect tomato plants and fruit and reduce yield. In the present study, Bacillus altitudinis B1-15 isolated from saline-alkali soil showed strong antifungal activity against B. cinerea. In pot experiments, a significant biocontrol efficacy of strain B1-15 was observed against tomato gray mold at 3-leaf stage (87.63%) and 6-leaf stage (76.43%), and the biocontrol efficacy was found to be 39.83% even after inoculation for 35 d at 6-leaf stage. A significant improvement of stem diameter, plant height, dry weight and fresh weight was also observed after tomato plants inoculated with strain B1-15. Strain B1-15, applied to tomato fruit by wounded or unwounded inoculation, could significantly inhibit gray mold and prolong the storage period of postharvest tomato fruit. The antifungal substances of strain B1-15 were found both in intraspore and extraspore, and the strain was also able to produce volatile organic compounds (VOCs), which could cause the mycelia of B. cinerea swelling and dehydrated malformation, the shortening of mycelia septum and the decomposition of cell wall and vacuole. Besides that, strain B1-15 could produce protease at a greater level, and chitinase and amylase at a lower level, which contributed to its antifungal activity. Additionally, 15 and 9 chemical compounds (similarity ≥ 80%) were individually identified from the crude extracts of the supernatant and precipitate of strain B1-15 via gas chromatography-mass spectrometry (GC–MS), including two VOCs 3-methylbutanoic acid and 2-methylbutanoic acid detected in both the supernatant and precipitate. Therefore, strain B1-15 could be used as a biocontrol agent and has great potential to control tomato gray mold and improve tomato yield and storage quality in practical production.