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Biological Control of Fusarium Crown Rot of Tomato by Trichoderma harzianum Under Field Conditions. A. Sivan, Research Assistant, Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel. Orna Ucko, and I. Chet. Agricultural Advisor for The Ministry of Agriculture Extension Service, Beer Sheva; and Professor, Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot. Plant Dis. 71:587-592. Accepted for publication 29 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0587.

Biological control experiments were carried out during two successive growing seasons in tomato fields naturally infested with Fusarium oxysporum f. sp. radicis lycopersici. Trichoderma harzianum was applied as a seed coating or as a wheat-bran/peat (1:1, v/v) preparation introduced into the tomato rooting mixture. Trichoderma-treated transplants were better protected (P = 0.05) against Fusarium crown rot than untreated controls when planted in methyl bromide-fumigated or nonfumgated infested fields. The total yield of tomatoes in the T. harzianum-treated plots was increased as much as 26.2% over the controls. When T. harzianum was applied to the root zone of tomato transplants, it proliferated successfully in the rhizosphere. Soil samples taken from the crown area 510 cm from the plant stem showed an increase in T. harzianum population levels during the growing season; however, no significant decline was found in the soil population density of Fusarium spp. in the same soil samples. When tomato seeds previously treated with conidia of T. harzianum were sown in a naturally infested field, the antagonist was detected on root segments from plants sampled 20 wk after planting. The highest counts of the antagonist were detected on the root tips, resulting in the complete reduction of Fusarium spp. recovered from these segments.