A Rapid and Accurate PCR-Based Method for Mating-Type Determination in the Heterothallic Oomycete <i>Plasmopara viticola</i> , the Causal Agent of Grapevine Downy Mildew

Plasmopara viticola is a heterothallic diploid oomycete responsible for grapevine downy mildew, one of the most damaging grapevine diseases worldwide. Since no rapid method for mating type characterization of strains is currently available, mating type identification must be performed through crossing assays, which are time-consuming. This study reports the development of two PCR-based molecular markers (MT_indel1 and MT_indel2) through genome sequencing and structural variant calling to distinguish between the mating-type alleles of the oomycete Plasmopara viticola. For both markers, P1 strains (Mat-a/Mat-b) exhibited a double-band profile, whereas P2 strains (Mat-a/Mat-a) displayed a single PCR band. The markers were validated on a set of 37 reference strains collected across Europe and showed perfect concordance with mating-type phenotypes determined by crossing tests. They provide a robust, sensitive, and inexpensive DNA-based detection system for mating-type identification in P. viticola, offering valuable insights into the pathogen’s reproductive biology and genetic diversity.