An integrated approach to creating scab-resistant apple: phytopathological testing and marker-assisted selection

The creation of highly scab-resistant apple genotypes increases the profitability and environmental friendliness of the production of this fruit crop. Early stage evaluation of the resistance using phytopathological testing and DNA markers allows to accelerate the process of breeding for this trait allows the use. The purpose of the study was to comprehensively assess resistance to the causative agent of scab of hybrid seedlings of apple obtained from crossing susceptible (Rennet Simirenko) and resistant (Modi) cultivars for the Rvi6 gene, using infectious background and marker assisted selection. A phytopathological analysis of 207 hybrid apple seedlings against the natural background of apple scab pathogen revealed 117 (56%) plants without scab lesions (0 points). The remaining seedlings had lesions of varying degrees. DNA marker analysis of the Rvi6 gene allowed identification of 105 plants (51%) with the Rvi6rvi6 genotype and 102 (49%) – rvi6rvi6, which is close to a theoretical segregation ratio 1:1 in the crosses of this type. Comparison of the results of infectious evaluation and DNA-marker analysis showed 98% coincidence of the presence of the resistance gene with no lesions. In general, the complex use of the phenotypic and molecular markers evaluation of the hybrid family for resistance to Venturia inaequalis (Cooke) G. Winter shows a high degree of agreement between the results of the methods. However, the discrepancy between the qualitative classes of reactions to infection and the results of molecular genetic analysis indicates an insufficient strength of the natural infectious background of the study year. The low efficiency of the development of the disease was due to the unfavorable weather and climatic conditions at the beginning of the vegetative period and the formation of infection, which were expressed in a higher average monthly temperature and a small amount of precipitation compared to the norm. Our results suggest an advantage, a comprehensive assessment of resistance to the scab pathogen using an infectious background and marker-assisted selection for the Vf gene (Rvi6) in which the first stage involves the selection of resistant samples against a natural infectious background, followed by confirmation of the presence of the desired gene using a DNA marker analysis.