Suppression of Early Stages of Fungus Development by Hydrogen Peroxide at Low Concentrations

Abstract

Hydrogen peroxide mediates some anti-infectional responses of plants. It is toxic to pathogenous bacteria and fungi. To evaluate its minimal fungitoxic amounts, it was applied to spores of the causal agents of cucurbit scab (Cladosporium cucumerinum) and rice blast (Magnaporthe grisea, formerly Pyricularia oryzae) over the broad concentration range (10(-2) to 10(-14) M). Spore germination and appressorium formation were examined. The dose-response dependence was found multimodal for both fungi. The inhibition of spore germination was maximal at 10(-2) M and practically disappeared at 10(-5) - 10(-6) M H2O2. However, weaker peroxide solutions had increased fungitoxicity. The inhibition of C. cucumerinum spore germination at 10(-11)- 10(-12) M was almost the same extent as at 10(-2) M H2O2. For M. grisea, two maxima of germination inhibition near 10(-7) M and 10-10 M H2O2 were found. Here, the toxicity was higher than at its millimolar concentration. M. grisea appressoria formation repeated the aforementioned pattern generally. Therefore, hydrogen peroxide can have an antifungal action at very low concentrations. Such small amounts of H2O2 might be sufficient for plant defense responses as well.