The role of a β-1,3-1,4-glucanase derived from Bacillus amyloliquefaciens FS6 in the protection of ginseng against Botrytis cinerea and Alternaria panax

Abstract

Gray mold and Alternaria blight, caused by Botrytis cinerea and Alternaria panax, respectively, are the most common diseases of ginseng (Panax ginseng), and cause significant yield losses and reduced quality. Previous field experiments revealed that treatment of ginseng with Bacillus amyloliquefaciens FS6 provided an excellent control against these two diseases, although its mechanism of action was unclear. In the present study, we demonstrated that the bacteria-free fermentation broth obtained from B. amyloliquefaciens FS6, a FS6-bgl strain of B. amyloliquefaciens overexpressing the bgl gene (encoding a β-1,3-1,4-glucanase), and purified recombinant β-1,3-1,4-glucanase can inhibit B. cinerea and A. panax both in vitro and in planta. The recombinant β-1,3-1,4-glucanase protein, BG-Ba, significantly inhibited the mycelial growth and spore germination of both A. panax and B. cinerea. Bacteria-free fermentation broth derived from FS6-bgl cultures overexpressing the bgl gene also inhibited mycelial growth and spore germination of A. panax and B. cinerea. The level of inhibition in the fermentation broth of the wild-type vs. the recombinant strain increased from 9 to 12% and 8 to 12% for the two pathogens, respectively. Inoculation assays on ginseng leaves indicated that the BG-Ba protein and the bacteria-free fermentation broth of the FS6-bgl strain provided significant protective effect against infection by A. panax and B. cinerea. The present study provides new information on the antimicrobial activity of FS6 and reveals that the use of β-1,3-1,4-glucanase alone has good potential for the management of ginseng diseases.