Inheritance of Apple (Malus × domestica (L.) Borkh) Resistance against Apple Scab (Venturia inaequalis (Cooke) Wint.) in Hybrid Breeding Material Obtained by Gene Pyramiding

Apple scab caused by the pathogenic fungus Venturia inaequalis causes significant damage to apples. The creation of apple-scab resistant varieties is considered an alternative to pesticide-based management. To evaluate R gene inheritance, 862 apple hybrid samples were analyzed and divided into populations depending on the resistance genes (Rvi6 and Rvi5) present in the parents’ genotypes and their combinations. The field evaluation was carried out in 2016–2018 using the international VINQUEST scab evaluation methodology, but the genes were identified using specific scab resistance-gene molecular markers. Parent plants were genotyped using 22 SSR markers. The study determined that the field resistance of apple scab is influenced not only by the resistance genes present in the genotype but also by the genetic background of the apple cultivar, the tree’s general health status and resistance to other diseases. It was found that the apple scab resistance genes Rvi6 (Vf) and Rvi5 (Vm) are inherited according to Mendelian laws, and when both genes are pyramided in offspring, they are inherited as separate genes. In general, the inheritance of both genes in the offspring is not a determining factor for apple field resistance, as field resistance to scab is influenced by a combination of several factors.