Biological Control of Fusarium Crown Rot of Tomato by Trichoderma harzianum Under Field Conditions

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Abstract
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 nonfumigated 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 5-10 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 infected field, the antagonist was detected on root segments from plants sampled 20 wk after planting. The highest counts of the antagonists were detected on the root tips, resulting in the complete reduction of Fusarium spp. recovered from these segments.