Virulence of Hungarian Plasmopara halstedii Isolates on Sunflower Differential Lines Carrying Pl6, Pl8, and PlArg Resistance Genes with Specific Instability of Pl8-Mediated Resistance

Sunflower downy mildew, caused by Plasmopara halstedii, remains one of the most destructive diseases worldwide. The genetic diversity of P. halstedii populations continues to challenge resistance breeding efforts. This study evaluates the effectiveness of key resistance genes against P. halstedii isolates collected in Hungary. Eight isolates were tested using the sunflower differential lines HA-335, RHA-419, and RHA-340, with the resistance genes Pl6, PlArg, and Pl8, respectively. Disease develo