Numerous fungi and bacteria, including existing biocontrol strains with known activity against soilborne fungal pathogens as well as isolates collected from the roots and rhizosphere of tomato plants growing in the field, were tested for their efficacy in controlling Fusarium wilt of tomato. Tomato seedlings were treated with the potential biocontrol agents in the greenhouse and transplanted into pathogen-infested field soil. Organisms tested included nonpathogenic strains of Fusarium spp., Trichoderma spp., Gliocladium virens, Pseudomonas fluorescens, Burkholderia cepacia, and others. Specific nonpathogenic isolates of F. oxysporum and F. solani collected from a Fusarium wilt-suppressive soil were the most effective antagonists, providing significant and consistent disease control (50 to 80% reduction of disease incidence) in several repeated tests. These isolates also were equally effective in controlling Fusarium wilt diseases of other crops, including watermelon and muskmelon. Other organisms, including isolates of G. virens, T. hamatum, P. fluorescens, and B. cepacia, also significantly reduced Fusarium wilt compared to disease controls (30 to 65% reduction), but were not as consistently effective as the nonpathogenic Fusarium isolates. Commercially available biocontrol products containing G. virens and T. harzianum (SoilGard and RootShield, respectively) also effectively reduced disease (62 to 68% reduction) when granules were incorporated into potting medium at 0.2% (wt/vol). Several fungal and bacterial isolates collected from the roots and rhizosphere of tomato plants also significantly reduced Fusarium wilt of tomato, but were no more effective than other previously identified biocontrol strains. Combinations of antagonists, including multiple Fusarium isolates, Fusarium with bacteria, and Fusarium with other fungi, also reduced disease, but did not provide significantly better control than the nonpathogenic Fusarium antagonists alone.
