Antifungal Effects of Volatiles Produced byBacillus subtilisAgainstAlternaria solaniin Potato

Antifungal activities of plant-beneficialBacillushave been widely studied in recent years. Numerous studies have studied the antifungal mechanisms of soluble non-volatile bioactive compounds such as lipopeptides and proteins produced byBacillusagainst soil-borne diseases. However, the antagonistic mechanisms of volatile organic compounds (VOCs) fromBacillusagainst airborne phytopathogens are still largely unknown, and the function ofAlternaria solanipathogenic genes has not been well identified. Here, we first isolated aBacillusstrain with strong antifungal activity and finally identified it asB. subtilisZD01. Then, the antagonistic mechanisms of VOCs produced by strain ZD01, againstA. solani, an airborne fungal pathogen that can cause early blight diseases of potato, were studied. We showed that VOCs produced by strain ZD01 can reduce the colony size and mycelial penetration and can cause serious morphological changes ofA. solani. Scanning electron microscope (SEM) observation showed that VOCs released by ZD01 could cause more flaccid and gapped hyphae ofA. solani. Also, we found that VOCs produced by ZD01 can inhibit the conidia germination and reduce the lesion areas and number ofA. solani in vivosignificantly. Meanwhile, based on gas chromatography/mass spectrometry (GC/MS) analysis, 29 volatile compounds produced by strain ZD01 were identified. Out of 29 identified VOCs, 9 VOCs showed complete growth inhibition activities againstA. solani. Moreover, we identified two virulence-associated genes (slt2andsod) inA. solani.slt2is a key gene that regulates the mycelial growth, penetration, sporulation, and virulencein vivoinA. solani. In addition,sodplays a significant role in the SOD synthetic pathway inA. solani. Results from qRT-PCR showed that the transcriptional expression of these two genes was down-regulated after being treated by VOCs produced by ZD01. These results are useful for a better understanding of the biocontrol mechanism ofBacillusand offer a potential method for potato early blight disease control.