Bacillus amyloliquefaciens strains control strawberry anthracnose through antagonistic activity and plant immune response intensification

Abstract

Anthracnose disease caused by Colletotrichum gloeoesporioides can have devastating effects on strawberry production. In addition to the use of fungicides, feasible strategies for controlling this disease include the application of beneficial microorganisms. In this study, we assayed the effects of two Bacillus amyloliquefaciens strains, PMB04 and PMB05, on the control of strawberry anthracnose. First, an in vitro inhibitory assay revealed that the hyphal growth of C. gloeosporioide SC01 was inhibited by PMB04 more strongly than by PMB05. We further found that the culture filtrate from PMB04 was lethal to the conidia of SC01. Meanwhile, PMB05 was previously demonstrated to be a rhizobacterium that intensifies plant immunity in response to bacterial elicitors. Thus, its effect on plant immune signals, such as the rapid reactive oxygen species (ROS) generation and callose deposition triggered by the conidia of SC01 on strawberry leaves, were evaluated in this study. The results showed that only the PMB05 strain could intensify the plant immune signals activated by SC01. In an inoculation assay, meanwhile, both strains exhibited superior efficacy in reducing the occurrence of anthracnose on strawberry seedlings and fruits. More specifically, PMB04 and PMB05 showed better ability to control anthracnose on fruits and seedlings, respectively. We concluded that both the lethal effect on spores caused by PMB04 and the intensification of plant immunity caused by PMB05 could be key factors in controlling strawberry anthracnose. More interestingly, we present a case in which a plant immune response-intensifying strain was applied to control strawberry anthracnose.