Bio control of Selected Oyster Mushroom Diseases and Contaminants Using Antagonistic Fungi and Bacteria

Abstract

Mushroom is widely cultivated as a protein rich vegetable in many countries of the world including Kenya. However, a number of harmful fungi are encountered and many of these act as competitor moulds thereby adversely affecting spawn-run, whereas others attack the fruiting bodies at various stages of crop growth producing distinct disease symptoms. Management of mushroom diseases and contaminants is complicated by the high restriction on the number of accepted pesticides. In addition, the pesticides may be harmful to human health and the environment, and are expensive to small scale farmers. The use of biocontrol agents provides an alternative to replace the existing synthetic pesticides. The aim of this study was to test antimicrobial activity of antagonistic bacteria, selected fungal endophytes and Engleromyces goetzei against mushroom pathogens and contaminants and their effects on mushroom mycelia. Phytochemicals present in E. goetzei were extracted by use of soxhlet apparatus, tested and identified as steroids, terpenoids, saponins, flavonoids and coumarins. The antimicrobial assays were conducted using the dual culture method where a 5 mm plug of actively growing pathogen/contaminant was inoculated on one end of a PDA plate and the plate was doubly inoculated with the antagonist. Colony growth of mushroom pathogens and contaminants in the dual plates were recorded and percentage inhibition calculated in relation to plates with pathogens alone which served as controls. All the experiments were done twice in completely randomized design (CRD) with five replicates. Data was subjected to analysis of variance (ANOVA) using SAS statistical package. Mean values of all treatments were tested for significant differences and separated using LSD. Endophyte LAF 59 (Laggera alata fungus) exhibited the strongest inhibitory activity with 76% inhibition of the mycelial growth of Penicillium digitatum, 46.5% for Aspergillus flavus and 65.8% for A. parasitica. The percent inhibition induced by B. amyloliquefaciens was 76% against Trichoderma harzianum, 79.1% against T. asperellum, 80.3% against Aspergillus sp., 82.4% against Penicillium sp., 75.6% against Mucor sp. and 65.3% against Rhizopus sp. Volatile organic compounds produced by Bacillus amyloliquefaciens were also effective against the pathogens tested. These results indicate that B. amyloliquefaciens and the bioactive endophytic fungi LAF 59 and LAF 13 can be suggested as important alternatives to reduce fungicide application in the control of mushroom diseases and contamination.