Integrated control of fusarium crown and root rot of tomato with Trichoderma harzianum in combination with methyl bromide or soil solarization

Combination of Trichoderma harzianum with soil solarization or with a reduced dose of methyl bromide, under field conditions, resulted in significant (p = 0.05) disease control of fusarium crown and root rot of tomato induced by Fusarium oxysporum f. sp. radicis-lycopersici (FORL). T. harzianum or soil solarization applied alone were ineffective in protecting the tomato plants from crown and root rot. Soil fumigation with a sub-lethal dose of methyl bromide (300 kg ha^-1) provided the same degree of protection as the recommended dose (750 kg ha^-1). Maximum disease control (48%) was obtained with a combination of T. harzianum and the reduced dose of the fumigant. Treatments that resulted in disease control also elicited a significant yield increase (p = 0.05). The highest yield improvement (105% over the control) was recorded in plots where the antagonist had been applied in combination with soil solarization. In plots not treated with T. harzianum, the rhizosphere soil contained low levels of Trichoderma spp. [10²-10³ colony-forming units (c.f.u.) g^-1 rhizosphere soil], and tomato root segments showed no evidence of colonization by the antagonist. High levels of Trichoderma (10⁴-10⁵ c.f.u. g^-1) were recovered from rhizosphere soil or crown segments of plants treated with the antagonist in combination with methyl bromide or soil solarization. Conversely, high population levels of Fusarium spp. (2 × 10⁵ - 3 × 10⁷ c.f.u. g^-1) were recorded in rhizosphere soil or on crown segments sampled from all treatments. The combination of T. harzianum with methyl bromide (300 kg ha^-1) or soil solarization reduced the final colonization level of Fusarium spp. on the crown surface by 76 or 94%, respectively. This study reveals that combination of T. harzianum with a sub-lethal dose of methyl bromide or with soil solarization is effective in controlling FORL in tomato.