Antimycotal activity of Collimonas isolates and synergy-based biocontrol of Fusarium wilt of tomato

In a continued effort to discover microorganisms with plant-protective properties, we characterized a collection of bacterial isolates from multiple geographic origins and belonging to the genus Collimonas, for their ability to inhibit in vitro the growth of a wide range of plant-pathogenic fungi and oomycetes. Isolate Collimonas arenae Cal35 showed the greatest all-round performance and was the single-best inhibitor of several of the tested pathogens, including Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt of tomato. In greenhouse trials, neither C. arenae Cal35 nor the control treatment, i.e., the commercially available Bacillus-based biofungicide Serenade Soil, was able to prevent symptom formation on tomato plants challenged with F. oxysporum f. sp. lycopersici. However, a mixture of Cal35 and Serenade Soil (referred to as Collinade) significantly reduced vascular discoloration and F. oxysporum f. sp. lycopersici-induced loss of shoot dry weight. In replicated field experiments, a Collinade application reduced vascular symptoms as well as the relative abundance of F. oxysporum in the root endosphere of F. oxysporum f. sp. lycopersici-challenged plants. We discuss the emerging property of “biocombicontrol” by Collimonas and Bacillus in the context of synergy-based formulations for the protection of crops against pathogens.