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 c inerea was investigated in laboratory, greenhouse, and field trials. Prelim inary nutrient activation at 21 degreesC accelerated subsequent germination of the antagonist at temperatures from 9 to 21 degreesC; at greater than o r equal to 18 degreesC, the germination time of preactivated T harzianum PI conidia did not differ significantly from that of B. cinerea. When coinocu lated with B. cinerea, concentrated inocula of preactivated but ungerminate d T harzianum P I conidia reduced in vitro germination of the pathogen by g reater than or equal to 87% at 12 to,25 degreesC; initially quiescent conid ia achieved this level of suppression only at 25 degreesC. Application of q uiescent T harzianum PI conidia to detached strawberry flowers in moist cha mbers 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 inf ection by 60% at 12 degreesC. Both quiescent and preactivated conidia signi ficantly reduced latent infection in greenhouse-gown strawberries at a mean temperature of 19 degreesC, whereas only preactivated conidia were effecti ve in the field at a mean temperature of WC on the day of treatment applica tion. An antagonistic mechanism based on initiation of germination in suffi ciently concentrated inocula suggests that at suboptimal temperatures the e fficacy of Trichoderma antagonists might be improved by conidia activation prior to application.