Location: Molecular Plant Pathology
Title: Self-inhibition of spore germination via reactive oxygen in the fungus Cladosporium cucumerinum, causal agent of cucurbit scab Authors
Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2012
Publication Date: November 14, 2012
Citation: Averyanov, A.A., Lapikova, V.P., Pasechnik, T.D., Zakharenkova, T.S., Baker, C.J. 2012. Self-inhibition of spore germination via reactive oxygen in the fungus Cladosporium cucumerinum, causal agent of cucurbit scab. European Journal of Plant Pathology. 131:541-550. Interpretive Summary: Fungal diseases of crops cause major losses for farmers each year. Many of these diseases start by the germination of the fungal spore on the leaf surface. By learning to disrupt critical mechanisms that are involved in spore germination we could reduce the amount of disease. This study asked why the rate of spore germination, for some fungal pathogens, decreases after an optimum concentration of spores is reached. The rate increases until this optimum spore concentration is reached. The study suggests that a self-inhibitor is produced when spores reach higher than optimal concentrations. This information will be of use to plant scientists who are devising new strategies to improve disease resistance in plants.
Technical Abstract: Cladosporium cucumerinum spore germination in vitro depended on spore suspension density. Different fungal isolates displayed maximum germination at different spore concentrations. For one isolate, maximum spore density was observed at both 18 and 25 °C, although germination percentage increased slightly at the higher temperature. Diffusates originating in other spore suspensions of the same isolate reduced germination percentage of spores taken at optimal concentration. The least effect occurred in diffusate taken from spores kept at their optimal concentration. Self-suppression of spore germination at unfavorable concentrations was diminished more or less by antioxidants (superoxide dismutase, catalase, mannitol or formate). The same compounds, added to spore diffusates, reduced their fungitoxicities. All diffusates generated superoxide radical (assayed by adrenalin oxidation sensitive to superoxide dismutase). This activity correlated positively with diffusate toxicity. Leaf inoculation of the susceptible cucumber cultivar at 18 °C with spore suspensions at extreme densities, at which they germinated poorly in vitro, led to less disease severity then that at optimal density. In contrast, no disease symptoms appeared at 25 °C. It is suggested that spores germinating at their extreme concentrations produced reactive oxygen species, suppressing the pathogen; this effect could reduce disease development at low temperatures. At high temperatures, however, this mechanism seems not to work, suggesting that plant infection may be reduced by other disease inhibiting factors.