Long-term survival of Plasmopara viticola oospores

A research was carried out in order to verify the long-term viability of Plasmopara viticola oospores. It is commonly assumed that oospores may survive across grapevines growing seasons, but no experimental evidence of this assumption has been provided to date. Grapevine leaves were collected from untreated plants in Emilia-Romagna in fall 2004 to 2008. Fragments of these leaves were kept in soil under natural conditions. In spring 2005 to 2009, part of the leaf fragments collected in the previous autumn were used to evaluate oospore germination using the floating disk bioassay; in spring 2009, the bioassay was also performed using the leaf residue collected in fall 2005 to 2007. Results demonstrated that P. viticola oospores remained viable for the whole period considered in this work, i.e., about 65 months (from fall 2004 to spring 2009).