First and third authors: Department of Chemistry and Biotechnology, Agricultural University of Norway, 1432 Ås, Norway; and second author: Department of Plant Pathology, The Norwegian Crop Research Institute, 1432 Ås, Norway
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Accepted for publication 13 August 2001.
The effect of preliminary nutrient activation on the ability of conidia of the antagonist Trichoderma harzianum (atroviride) P1 to suppress Botrytis cinerea was investigated in laboratory, greenhouse, and field trials. Preliminary nutrient activation at 21°C accelerated subsequent germination of the antagonist at temperatures from 9 to 21°C; at ≥18°C, the germination time of preactivated T. harzianum P1 conidia did not differ significantly from that of B. cinerea. When coinoculated with B. cinerea, concentrated inocula of preactivated but ungerminated T. harzianum P1 conidia reduced in vitro germination of the pathogen by ≥87% at 12 to 25°C; initially quiescent conidia achieved this level of suppression only at 25°C. Application of quiescent T. harzianum P1 conidia to detached strawberry flowers in moist chambers reduced infection by B. cinerea by ≥85% at 24°C, but only by 35% at 12°C. Preactivated conidia reduced infection by ≥60% at 12°C. Both quiescent and preactivated conidia significantly reduced latent infection in greenhouse-grown strawberries at a mean temperature of 19°C, whereas only preactivated conidia were effective in the field at a mean temperature of 14°C 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.
© 2001 The American Phytopathological Society