ABSTRACT This study investigated the sexual reproduction of Plasmopara viticola in wine regions of southern Brazil. Leaves with mosaic symptoms from susceptible hosts of Vitis vinifera were collected from vineyards in the autumn and screened for the presence of oospores. Leaves from hosts carrying different resistance alleles were also collected in three contrasting environments in Santa Catarina State; the influence of these factors on oospore formation was assessed. Georeferenced oospore records were used in the maximum entropy ecological niche model (MaxEnt) and climatic suitability for oospore formation in southern Brazil was determined. Finally, oospore germination assays were conducted after overwintering under natural conditions in both susceptible and partially resistant hosts. Oospores were detected in all vineyards investigated. The interaction between resistance alleles and the environment influenced oospore formation. Oospores were formed in all partially resistant hosts, even those with pyramided resistance alleles. Ecological niche modelling indicated that 80.8% of southern Brazil has moderate to very high suitability for oospore formation. This is the first study to confirm P. viticola oospore formation in all major wine‐growing regions of southern Brazil, oospore germination under local conditions in susceptible and resistant hosts, and to apply ecological niche modelling to predict climatic suitability for oospore formation. These findings expand the known distribution of the sexual cycle of P. viticola in the southern hemisphere confirming its sexual reproduction in southern Brazil with critical implications for grapevine breeding and disease management, as sexual reproduction promotes genetic diversity, increasing the risk of host resistance breakdown and fungicide resistance.
Bitencourt et al. (Fri,) studied this question.