Isolation and characterization of a cold-tolerant strain of Fusarium proliferatum, a biocontrol agent of grape downy mildew

A cold-tolerant strain of the mycoparasite Fusarium proliferation was isola ted following UV mutagenesis of the G6 strain, which is a biocontrol agent of grape downy mildew. Tbe isolated strain (designated 1505) exhibited radi al growth two to threefold that of the parent strain when grown at 13 degre esC, which is generally suboptimal for growth of Fusarium spp., but desirab le for its host, Plasmopara viticola. This rapid growth was correlated with improved biological control of P. viticola, determined by a detached-leaf assay. Even though radial growth of strain 1505 at higher temperatures was slower than that of G6 and the strain failed to conidiate, there was no red uction in biocontrol efficacy. Significantly higher levels of extracellular beta -glucosidase and endo-1,4-beta -glucanase activity were measured in t he culture filtrate of strain 1505 relative to that of strain G6. A DNA-med iated transformation procedure that included the introduction of antibiotic resistance and a GUS reporter gene system was adapted for F proliferatum. Using the GUS-engineered strains, we demonstrated that both G6 and 1505 exh ibit the characteristic coiling and penetration of host structures.