pH and water activity in culture media affect biological control activity of Trichoderma atroviride against Rhizoctonia solani

Abstract Biological control activity of Trichoderma spp. is heavily influenced by abiotic factors. Effects of pH and water activity ( a w ) in culture media of Trichoderma atroviride LU132 were assessed on conidium production, germination percentage and bioactivity against a soil-borne pathogen Rhizoctonia solani in dual agar culture assays. The effects of pH and buffer capacity in media were tested on T. atroviride colonies using different proportions (50, 100, 200 and 400 mM) of phosphate buffers at pHs of 3.5, 4.5, 5.5, 6.5, 7.5 or 8.5. Water activity experiments tested different a w values (0.998, 0.995, 0.985, 0.977, 0.961 and 0.948). Conidium production was reduced with increasing phosphate buffer concentrations from 50 to 400 mM. Maximum germination, and inhibition activity against R. solani was measured for conidia obtained from medium at pH 7.5. Greatest conidium production occurred at a w 0.995 and the least at a w 0.948. Mean conidium germination was greatest (78%) from media at a w 0.961, and least (21%) from a w 0.985. Inhibition and overgrowth activities of Trichoderma colonies were greatest at a w 0.961 and least at a w 0.998. This study has demonstrated that manipulation of culture conditions as such may improve conidium fitness (quantity and quality). However, these factors may not have caused independently effects on the fungus. Effects of physical growth conditions (besides nutritional requirements) are likely to be important for optimum production of biocontrol agents based on T. atroviride LU132, and other similar biocontrol agents.