Age-dependent Grey Mould Susceptibility and Tissue-specific Defence Gene Activation of Grapevine Berry Skins after Infection by Botrytis cinerea

The correlation between the degree of maturity of grapevine berries and their susceptibility to infection by the grey mould fungus Botrytis cinerea was studied. Artificial inoculation with B. cinerea conidia of detached berries from cultivars Riesling and Pinot noir revealed an increasing susceptibility during the last weeks of berry ripening. Wound inoculation resulted in increased lesion formation when compared with inoculation of non-wounded berry skins. Lesion development after non-wounding inoculation was stimulated by the addition of nutrients. Riesling berries were more readily infected than Pinot noir berries, indicating that the Riesling berry skin is more easily colonized by the grey mould fungus. Analysis of defence gene activation in the berry skin tissue revealed increased transcript levels of phenylalanine ammonium lyase and stilbene synthase after inoculation with B. cinerea conidia, while mRNA abundance of osmotin was similar in inoculated and non-inoculated tissue. Our data indicate that properties of the grape berry skin, including its ability for infection-induced defence gene activation, are important for the outcome of grey mould infections