Is the mycoparasitic activity of Ampelomyces quisqualis biocontrol strains related to phylogeny and hydrolytic enzyme production?

The use of mycoparasites is a highly elegant method of biocontrol, as the agent is specific and can expand its activity on its own, and it presents no risk to the environment. Ampelomyces quisqualis best typifies the potential of mycoparasites, as it is highly specific to powdery mildews, does not produce any toxic metabolites and can easily be mass-produced in vitro. However, the level of parasitization varies between strains, and the cause of this variation is unknown. In this study, twenty-four selected strains isolated from different host mildews and possessing different ITS rDNA sequences were evaluated for their ability to colonize cucumber, grapevine and strawberry powdery mildews and for in vitro production of cell wall degrading enzymes (CWDEs). Individual strains differed significantly in enlargement of the colonization area by intra-hyphal formation of pycnidia within powdery mildew colonies and in inhibition of host conidation. Pronounced differences in the in vitro activity of chitobiases, proteases and β-1,3-glucanases were also observed between strains. We found a positive correlation between mycoparasitic activity and chitobiases and proteases but not glucanases. Furthermore, principal component analysis showed that A. quisqualis strains with similar levels of mycoparasitic activity originated from the same host species and shared an identical ITS rDNA sequence. These results provide a deeper understanding of the process of mycoparasitism and a sound basis for developing new screening strategies for detecting highly effective A. quisqualis strains in the biocontrol of powdery mildews.