Antagonism of nutrient-activated conidia of Trichoderma harzianum (atroviride) P1 against Botrytis cinerea

The effect of preliminary nutrient activation on the ability of conidia of the antagonist Trichoderma harzianum (atroviride) PI to suppress Botrytis cinerea was investigated in laboratory, greenhouse, and field trials. Preliminary nutrient activation at 21 degreesC accelerated subsequent germination of the antagonist at temperatures from 9 to 21 degreesC; at greater than or equal to 18 degreesC, the germination time of preactivated T harzianum PI conidia did not differ significantly from that of B. cinerea. When coinoculated with B. cinerea, concentrated inocula of preactivated but ungerminated T harzianum P I conidia reduced in vitro germination of the pathogen by greater than or equal to 87% at 12 to,25 degreesC; initially quiescent conidia achieved this level of suppression only at 25 degreesC. Application of quiescent T harzianum PI conidia to detached strawberry flowers in moist chambers reduced infection by B. cinerea by greater than or equal to 85% at 24 degreesC, but only by 35% at 12 degreesC. Preactivated conidia reduced infection by 60% at 12 degreesC. Both quiescent and preactivated conidia significantly reduced latent infection in greenhouse-gown strawberries at a mean temperature of 19 degreesC, whereas only preactivated conidia were effective in the field at a mean temperature of WC on the day of treatment application. An antagonistic mechanism based on initiation of germination in sufficiently concentrated inocula suggests that at suboptimal temperatures the efficacy of Trichoderma antagonists might be improved by conidia activation prior to application.