Nutrient amendments affect Trichoderma atroviride conidium production, germination and bioactivity

• Medium composition affected conidium production, germination and bioactivity.
• Large amounts of carbohydrate decreased conidium fitness.
• Low amounts of carbohydrate increased conidium fitness.
• C:N ratios near 5:1 were likely optimum for conidium production and bioactivity.
• Results obtained could be generalised for Trichoderma-based biocontrol products.

Trichoderma atroviride LU132, the active organism in two commercialised biological control products, was grown under different in vitro culture carbon to nitrogen ratios, to assess effects on conidium production, germination and bioactivity. Sucrose as a carbon source in agar-based growth media was adjusted to 4.2, 8.4, or 16.8 g/l carbon, and soy peptone as a nitrogen source to 0.03, 0.05, 0.11, 0.21, 0.42, 0.84, 1.68, or 3.36 g/l, to give C:N ratios in the growth media ranging from 5:1 to 160:1. Conidium production was greatest at 16.8 g/l carbon and least at 4.2 g/l, and was prolific at C:N 5:1, but was sparse at C:N 160:1. Mean conidium germination was greatest (68%) at 4.2 g/l carbon and least (58%) at 16.8 g/l carbon. Germination was greatest (74%) for C:N 5:1 and least (52%) for C:N 160:1. Trichoderma inhibition activity against the diseases-causing Rhizoctonia solani was also affected slightly for colonies obtained from conidia grown on media with 4.2 g/l carbon from 67% to 70% with 16.8 g/l carbon. Inhibition activity was greatest (73%) from conidia produced at C:N 5:1 and least (63%) from C:N 160:1. Low amounts of carbohydrate in growth media at C:N ratios near 5:1 were optimum for growth of T. atroviride LU132. Large amounts of carbohydrate probably repressed carbon catabolism, resulting in decreased conidium fitness. These results provide new knowledge to assist commercial production of biocontrol agents based on T. atroviride LU132.

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