Microbial Fungicides in the Control of Plant Diseases

As environmental and commercial requirements for new fungicides are increasingly demanding, antifungal compounds of microbial origin attract tremendous interest as a starting point in the development of environmentally sound agricultural fungicides. As seen in fenpiclonil, fludioxonil and synthetic derivatives of the strobilurins such as azoxystrobin and krexosim‐methyl, this approach for the development of microbial fungicides has proven to be a promising and effective strategy for developing new fungicides. As a result, microbial metabolites face a revival as lead compounds. Recently, numerous antifungal compounds were discovered from diverse microbial sources using traditional activity‐based screening techniques. These microbial compounds showed potent control efficacy against various plant diseases, including chronic diseases which are difficult to control with conventional synthetic fungicides. Advances in screening systems directed to specific targets of fungal metabolism have increased the opportunities to discover novel antifungal agents with selectivity over non‐target organisms. Microbial metabolites have also been exploited as a source for non‐fungicidal disease control agents that do not inhibit vegetative hyphal growth, but rather interfere specifically with the infection process of pathogenic fungi. The specificity of microbial fungicides is a highly preferred characteristic in terms of impacting the environment, where it is closely related to the occurrence of fungicide resistance. The most recently developed fungicides from microbial metabolites, the strobilurins, provide a cue for the high risk of resistance development of site‐specific fungicides.