Inhibitory mechanism of Bacillus amyloliquefaciens subsp. plantarum CGMCC 11640 against Botryosphaeria dothidea , the pathogen of canker disease of Carya cathayensis

Abstract

The canker disease of Carya cathayensis caused by Botryosphaeria dothidea, is one of the diseases in China that has resulted in serious damage and even death for the tree. To overcome the serious disease threat to the C. cathayensis industry, Bacillus amyloliquefaciens subsp. plantarum CGMCC 11640, which has shown a strong inhibitive activity in vitro against Botryosphaeria dothidea, was obtained by screening with the dual-culture method and cultured in medium mixtures with ratios of sterilized fermentation supernate to PDA being 1:9, 2:8, and 5:5(volume ratio). Then, the inhibitory mechanisms of strain CGMCC 11640 against Botryosphaeria dothidea were further explored by scanning electron microscopy (SEM). Results revealed that the Botryosphaeria dothidea strain growth rate for the three volume ratio mediums were restrained by 75.8% for 1:9, 88.8% for 2:8, and 94.3% for 5:5. The SEM results showed that both bacterial cells and their sterilized fermentation supernate exhibited strong inhibition activity in vitro against Botryosphaeria dothidea and that the hyphae and spores of Botryosphaeria dothidea exhibited atrophy and introcession. Thus, CGMCC 11640 inhibited Botryosphaeria dothidea by destroying cell membranes (e.g. punching holes in them) and walls of hyphae and spores resulting in leakage of plasmatic material from the inside of the cells.