Biological Control Effects of a New Isolate ofTrichoderma harzianumonPythium aphanidermatum

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Abstract
A wheat-bran plus peat mixture (1:1 vol/vol) was the most efficient of the raw plant material substrates (which included several agricultural plant wastes) found suitable for growing a new isolate of T. harzianum (T-315). The bran/peat preparation of T. harzianum, applied to either soil or rooting mixture, efficiently controlled damping-off induced by P. aphanidermatum in peas [Pisum sativum cv. Perfection], cucumbers [Cucumis sativus cv. Alma], tomatoes [Lycopersicon esculentum cv. Rehovot 13], peppers [Capsicum annuum cv. Maor] and gypsophila [Gypsophila paniculata cv. Bristol Fairy]. Disease reduction of up to 85% was obtained in tomatoes. T. harzianum applied in a seed coating mixture containing 5 .times. 109 conidia/ml was as effective in sandy soil as the broadcast application of wheat bran/peat preparation. However, the broadcast application was superior to seed coating for protecting tomato seedlings in an infested peat/vermiculite rooting mixture. When germinated at low temperature (22.degree. C) pea seeds coated with conidia of T. hamatum were better protected from P. aphanidermatum than seeds with T. harzianum, but this was not the case at 30.degree. C. Extracellular filtrate from cultures of T. harzianum, added to a synthetic medium, inhibited linear growth of P. aphanidermatum by 83% compared with 8% inhibition by a culture filtrate of T. hamatum. Substances excreted by P. aphanidermatum into the growth medium enhanced the linear growth of T. harzianum by 34%, but not that of T. hamatum.