Microbial compost tea properties affect suppression of strawberry grey mould (Botrytis cinerea Pers.)

Compost teas are aqueous filtrates of steeped composted materials, which can be applied to the phyllosphere or rhizosphere of plants. Compost teas possess beneficial effects including reducing the impact of plant pathogens. Six compost teas were prepared and tested for their ability to inhibit mycelial growth of strawberry pathogens and to suppress grey mould of strawberry. All compost teas inhibited the growth of Alternaria alternata, Botrytis cinerea, Phytophthora fragariae, and Verticillium dahliae, by 45-73%. Compost teas prepared from forest, sea, sheep, shrimp, and vermicomposts reduced grey mould lesions on strawberry leaves by 38-62% up to 12 days. Heat and cold sterilised compost teas did not provide inhibition of B. cinerea, indicating that presence of microorganisms seemed key to the activity of the compost tea. Total bacteria, Gram negative bacteria, and fungal/oomycete population numbers did not relate to effectiveness of the compost teas. Three isolates from sheep compost tea showed antibiosis-like activity. Isolates SH1 and SH2 resembled Bacillus velezensis and isolate SH3 resembled Pseudomonas azotoformans, following sequence analysis and phylogenetic relatedness testing. Results indicated that pathogen inhibition and grey mould suppression did not seem related to different microbial community groups or population numbers, but rather to the general presence of specific microbial groups or individual antagonistic microorganisms.