Assessing aerated vermicompost tea (ACT) combined with microbial biological control agents for suppression of Fusarium and Rhizoctonia.

Biological control of plant diseases is important in organic greenhouse vegetable production where fungicide use is limited. Organic producers employ microbially-diverse substrates, including composts, as media for plant growth. Previous research into the impact of vermicompost on the efficacy of applied biocontrol agents is limited. An in vitro assay was developed to test the efficacy of two biological control agents in a competitive microbial background. Suppression of the pathogen Fusarium oxysporum f. sp. radicis-cucumerinum (Forc) by Clonostachys rosea f. catenulata (Gliocladium catenulatum strain J1446 (Prestop®) and Bacillus subtilis strain QST 713 (Rhapsody®), was assessed on agar media amended with aerated vermicompost tea (ACT). Pathogen growth was reduced more by C. rosea than ACT alone and C. rosea was equally effective when combined with ACT. In contrast, B. subtilis reduced pathogen growth less than ACT, and when combined, reduced pathogen growth not more than ACT alone. Both biocontrol agents were similarly tested with ACT against Forc and Rhizoctonia solani on cucumber and radish. Additive, neutral, and antagonistic responses, depending on host, pathogen, and biocontrol agent, were observed. ACT alone provided more consistent disease suppression on cucumber compared with B. subtilis or C. rosea. In combination, disease suppression was most often better than each biocontrol alone but not better than ACT alone. ACT had antagonistic or additive interactions with C. rosea in the radish/R. solani pathosystem, depending on the experiment. The specific and general suppression of plant diseases by biological control agents in microbially-rich environments is variable and requires further study.