Genetics and Molecular Marker Identification of a Resistance to Glomerella Leaf Spot in Apple

Abstract

Apple Glomerella leaf spot (GLS) is a destructive fungal disease that damages apple leaves during the summer in China. Breeding new disease-resistant varieties is considered to be the best way of controlling GLS. A genetic study of resistance to Glomerella leaf spot (GLS) in apple was conducted by using four F1 hybrid groups (‘Fuji’ × ‘Golden Delicious’, ‘Golden Delicious’ × ‘Fuji’, ‘Gala’ × ‘Fuji’, and ‘Fuji’ × ‘QF-2’) generated from two highly resistant varieties or selections, ‘Fuji' and ‘QF-2’, and two highly susceptible varieties, ‘Golden Delicious’ and ‘Gala’. The results showed that the separation ratios of resistant plants to the susceptible ones in the four F1 hybrid groups were statistically consistent with the theoretical ratios of 1:1, 1:1, 0:1, and 1:0. Comprehensive analysis enabled us to generate the following conclusions: GLS resistance in apple may be controlled by a single recessive gene. The genotype of the resistant plants was rr, whereas the genotypes of the susceptible ones were RR and Rr. By using ‘Golden Delicious’ × ‘Fuji’ F1 hybrid groups and the bulked segregation analysis (BSA) method, the marker S0506206-243bp associated with disease resistance character to GLS was identified through screening 500 SSR primers encompassing the entire apple genome with even coverage, and the genetic distance between the marker and the GLS resistance gene was 9.8 cM.