AUTHOR=Zhang Dai , Yu Shuiqing , Yang Yiqing , Zhang Jinglin , Zhao Dongmei , Pan Yang , Fan Shasha , Yang Zhihui , Zhu Jiehua 

TITLE=Antifungal Effects of Volatiles Produced by Bacillus subtilis Against Alternaria solani in Potato

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01196

DOI=10.3389/fmicb.2020.01196

ISSN=1664-302X

ABSTRACT=<p>Antifungal activities of plant-beneficial <italic>Bacillus</italic> have 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 by <italic>Bacillus</italic> against soil-borne diseases. However, the antagonistic mechanisms of volatile organic compounds (VOCs) from <italic>Bacillus</italic> against airborne phytopathogens are still largely unknown, and the function of <italic>Alternaria solani</italic> pathogenic genes has not been well identified. Here, we first isolated a <italic>Bacillus</italic> strain with strong antifungal activity and finally identified it as <italic>B. subtilis</italic> ZD01. Then, the antagonistic mechanisms of VOCs produced by strain ZD01, against <italic>A. solani</italic>, 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 of <italic>A. solani</italic>. Scanning electron microscope (SEM) observation showed that VOCs released by ZD01 could cause more flaccid and gapped hyphae of <italic>A. solani</italic>. Also, we found that VOCs produced by ZD01 can inhibit the conidia germination and reduce the lesion areas and number of <italic>A. solani in vivo</italic> significantly. 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 against <italic>A. solani</italic>. Moreover, we identified two virulence-associated genes (<italic>slt2</italic> and <italic>sod</italic>) in <italic>A. solani</italic>. <italic>slt2</italic> is a key gene that regulates the mycelial growth, penetration, sporulation, and virulence <italic>in vivo</italic> in <italic>A. solani</italic>. In addition, <italic>sod</italic> plays a significant role in the SOD synthetic pathway in <italic>A. solani</italic>. 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 of <italic>Bacillus</italic> and offer a potential method for potato early blight disease control.</p>