Effect of temperature and nutrient stress on the capacity of commercial Trichoderma products to control Botrytis cinerea and Mucor piriformis in greenhouse strawberries

Three commercial Trichoderma products (Trichodex, Binab TF WP, and Rootshield) and the laboratory strain T. harzianum Fl were sprayed weekly onto greenhouse-grown strawberry plants during the flowering period in an attempt to reduce fruit disease caused by Botrytis cinerea and Mucor piriformis. None of the treatments affected the marketable yield of strawberries. Laboratory tests showed that at the mean temperature of the greenhouse (12 degrees C), formulated conidia of the various Trichoderma strains required up to 96 h to germinate, and conidia of B. cinerea and M. piriformis isolated from greenhouse strawberries required 11 and 16 h, respectively. Furthermore, the commercially formulated conidia were much more subject to fungistasis under nutrient stress in vitro than were fresh conidia of the same strains. This nutrient sensitivity was not revealed when assaying germination on a standard nutrient-rich laboratory medium. Formulated conidia were also inferior to fresh conidia in capacity to colonize senescent strawberry leaves. We conclude that not only were the Trichoderma strains tested unable to germinate as quickly as B. cinerea and M. piriformis at the ambient temperatures of the greenhouse, but also that the commercially formulated conidia lost the capacity to germinate on and effectively colonize nutrient-poor natural substrates. These findings may be relevant not only to the lack of disease control shown in the present application but also to the inconsistent performance of these products reported in other trials. (C) 2000 Academic Press.