Oomycetes are fungal-like pathogens that cause notorious diseases. Protecting crops against oomycetes requires regular spraying with chemicals, many of which with unknown mode of action. In the 1990’s, flumorph was identified as a novel crop protection agent. It was shown to inhibit the growth of oomycete pathogens including Phytophthora species, presumably by targeting actin. We recently generated transgenic Phytophthora infestans strains that express Lifeact-eGFP, which enabled us to monitor the actin cytoskeleton during hyphal growth. For analyzing effects of oomicides (8) on the actin cytoskeleton in vivo, the P. infestans Lifeact-eGFP strain is an excellent tool. Here we confirm that flumorph is an oomicide with growth inhibitory activity. Microscopic analyses showed that low flumorph concentrations provoked hyphal tip swellings accompanied by accumulation of actin plaques in the apex, a feature reminiscent of tips of non-growing hyphae. At higher concentrations swelling was more pronounced and accompanied by an increase in hyphal bursting events. However, in hyphae that remained intact, actin filaments were indistinguishable from those in non-treated, non-growing hyphae. In contrast, in hyphae treated with the actin depolymerising drug latrunculin B, no hyphal bursting was observed but the actin filaments were completely disrupted. This difference demonstrates that actin is not the primary target of flumorph.
- oomycete aphanomyces-euteiches
- plant pathogen