Molecular screening of ‘Aport’ apple on Malus sieversii rootstock for resistance to scab and powdery mildew 

Abstract

Apple (Malus domestica Borkh.) is an economically important fruit crop in Kazakhstan, where its wild progenitor, Malus sieversii, represents a valuable source of genetic diversity and disease resistance. Apple scab (Venturia inaequalis) and powdery mildew (Podosphaera leucotricha) are among the most destructive fungal diseases limiting apple production. This study aimed to identify resistant M. sieversii rootstocks using integrated phytopathological and molecular analyses of graft combinations with the cultivar ‘Aport’. Field evaluations conducted during 2023–2025 revealed considerable variation in disease resistance among 11 scion–rootstock combinations. Forms №4, №7, №9, and №10 remained free of symptoms of both diseases throughout the study period, whereas forms №3, №5, and №8 exhibited moderate susceptibility to apple scab. The PCR screening identified scab resistance loci Rvi6 (forms №2, №3, №7, and №10), Rvi2/Rvi8 (№8, №9, and №10), Rvi5 (№7 and №10), and Rvi14 (№2, №7, and №10). Powdery mildew resistance was associated with the Pl1 locus, which was detected in all analyzed forms, while Pl2 was identified only in forms №2 and №10, and Pl-w in forms №3, №10, and №18. Form №10 exhibited the most favuorable genetic profile, combining multiple scab and powdery mildew resistance loci with complete field resistance. The results demonstrate the effectiveness of integrating molecular markers with field assessment for identifying resistant apple germplasm and highlight promising donor genotypes for breeding disease-resistant cultivars adapted to Kazakhstan.