Compost teas provide reduction of grey mould (Botrytis cinerea Pers.) on tomato plants

Compost teas are watery fermented extracts with proven suppressive effects against plant pathogens. Compost teas were prepared from six different compost sources and assayed for in vitro effects against Botrytis cinerea growth. In vivo, weekly foliar application of compost teas on tomato plants and a tomato leaflet trial with undiluted and 10 × diluted teas were conducted to assess effects on grey mould caused by B. cinerea. Results showed that all tested compost teas inhibited B. cinerea growth when unsterilized. Heat- and cold-sterilization of compost teas reduced or eliminated inhibitory effects, suggesting that the presence of microorganisms is essential for inhibitory efficacy. When used as foliar sprays, bovine manure (BOV), shrimp (SHR), and garden-leaves-straw (GLS) compost teas effectively reduced disease severity for six weeks. In leaflet trials, BOV, GLS, and garden waste (GAR) compost teas caused the greatest delay in grey mould lesion expansion. Moreover, BOV, GLS, and, in particular, SHR compost teas were equally effective in undiluted and diluted form. Microbial characterization showed varying microbial compositions across all compost teas, with notably large populations of fungi or oomycetes and Pseudomonas spp. in GLS. There was no clear relationship between the source of compost (manure, other animal by-product, solely plant-based) and efficacy against grey mould. Results also indicate that the abundance of microbial populations and subpopulations did not correlate with the inhibitory effects of the teas. The diversity of microbial populations or the presence of particular microbial species is more likely to be a determining factor of compost tea efficacy.