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

• pH and water activity in culture media affected conidium quality.
• Medium buffer capacity and pH are factors determining Trichoderma bioactivity.
• Low aw and high pH in production gave rapid germination and high bioactivity.
• Culture conditions are not independent factors, but interact with each other.

Biological control activity of Trichoderma spp. is heavily influenced by abiotic factors. Effects of pH and water activity (aw) 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 aw 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 aw 0.995 and the least at aw 0.948. Mean conidium germination was greatest (78%) from media at aw 0.961, and least (21%) from aw 0.985. Inhibition and overgrowth activities of Trichoderma colonies were greatest at aw 0.961 and least at aw 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.

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