Department of Chemistry and Biotechnology, Agricultural University of Norway, N-1432 Ås, Norway
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Accepted for publication 9 July 2003.
Trichoderma biocontrol isolates are most effective as highly concentrated inocula. Their antagonism to other fungi may be a result of pregermination respiration. In a nutrient-rich medium, almost all Trichoderma atroviride P1 (P1) conidia initiated germination processes and increased respiration, even in dense suspensions. When 1 × 107 P1 conidia/ml were coinoculated with 1 × 105 Botrytis cinerea conidia/ml, dissolved oxygen fell to <1% within 2 h and the pathogen failed to germinate. More dilute P1 suspensions consumed oxygen slowly enough to allow coinoculated B. cinerea to germinate. On nutrient-poor media, fewer P1 conidia initiated germination. Oxygen consumption by the inoculum and inhibition of B. cinerea were enhanced when P1 conidia were nutrient activated before inoculation. Pregermination respiration also affected competitive capacity of the antagonist on solid substrates, where respiratory CO2 stimulated germination rate and initial colony growth. These parameters were directly correlated with inoculum concentration (R2 ≥ 0.97, P < 0.01). After initiating germination, Trichoderma conidia became more sensitive to desiccation and were killed by drying after only 2 h of incubation on a nutrient-rich substrate at 23°C. These results indicate that nutrient-induced changes preceding germination in Trichoderma conidia can either enhance or decrease their biological control potential, depending on environmental conditions in the microhabitat.
© 2003 The American Phytopathological Society