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Antifungal and antioomycete properties of California Collimonas isolates and their use in synergy-based biocontrol of Fusarium wilt of tomato
H. K. DOAN (1), N. Maharaj (1), E. Miyao (2), R. M. Davis (3), J. H. Leveau (3). (1) Univ of California, Davis, CA, U.S.A.; (2) University of California, Woodland, CA, U.S.A.; (3) University of California, Davis, CA, U.S.A.

The bacterial genus <i>Collimonas</i> comprises three species: <i>C. fungivorans, C. pratensis</i>, and <i> C. arenae</i>.  Collimonads are best known for their mycophagous, weathering, and antifungal properties. A total of five <i>Collimonas</i> isolates from Northern California forest soils were tested along five strains from the Netherlands and one from Japan for their ability to inhibit the growth of phytopathogenic fungi and oomycetes <i>in vitro</i>. Of the collimonads tested, <i>C. arenae</i> Cal35, was by far the most antagonistic in these confrontation assays. <i>Collimonas arenae</i> Cal35 showed the greatest antagonism against <i>Fusarium oxysporum</i> f. sp. <i> lycopersici</i> (FOL), the causal agent of Fusarium wilt of tomato, and <i>Verticillium dahliae</i>, the causal agent of Verticillium wilt of tomato. In greenhouse trials, Fusarium wilt of tomato was effectively controlled by a mixture of <i>C. arenae</i> Cal35 and a commercially available, <i> Bacillus</i>-based biofungicide, but not by either one alone. Tomato plants had reduced vascular discoloration and increased shoot dry weight with soil drenches of the mixture of <i> C. arenae</i> Cal35 and the <i> Bacillus</i>-based biofungicide. In field experiments, application of this mixture reduced the incidence of FOL in tomato plants and increased fruit yield. In addition, this mixture reduced fruit sunburn and prevented FOL-induced loss of plant foliage.

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