Chemical Hormesis on Plant Pathogenic Fungi and Oomycetes

摘要

Hormetic effects of fungicides on fungi and oomycetes include moderate increase in growth rate, secondary metabolite production, and disease severity by plant pathogens. Hormesis has been documented in plant pathogens for exposure to low-doses of fungicides with both high and low fungicide resistance risk. Exposure to sub-inhibitory doses of fungicides can occur from improper use (e.g., over use of an active ingredient, poor application technique, or dilution of fungicide solutions in recirculation systems) or from natural degradation of the active ingredient, which may also lead to selection of fungicide resistant strains. One of the main challenges of chemical hormesis research is reproducibility. Systematic and meticulous screening and selection of target organisms, optimal mycelial age, chemical stressors and appropriate endpoints are required elements in experimental design for hormesis studies. Furthermore, multiple replicates and assay repetitions are necessary to ensure reproducibility and accuracy. Attempts to elucidate the mechanisms behind chemical hormesis have been fruitless so far. However, recent research suggests that increased mutation rates may result from exposure to sublethal doses of fungicides in fungi. Awareness of the risks associated to hormetic stimulation of fungi and oomycetes among scientists, educators, growers and the general public is necessary to prevent aggravated damages and crop losses that may result from accidental stimulation of pathogens.