LAUSR

Glomerella leaf spot (GLS) is a new fungal disease of apple that damages apple leaves mainly during the summer in China. For efficient GLS-resistant apple breeding by marker-assisted selection (MAS) and a better understanding of the molecular mechanisms of the resistance, it is important to find molecular markers that are tightly linked to GLS resistance genes and construct fine mapping. However, the development and selection of DNA markers are time-consuming and labor-intensive processes. Next-generation sequencing technology provides a powerful tool to overcome this limitation and is faster and more efficient in establishing the association of GLS resistance with molecular markers or searching for candidate genes. In this study, we report a method for rapid location of a GLS resistance gene locus (Rgls) in apple by whole genome re-sequencing technology coupled with bulked segregant analysis (BSA). A total of 3,399,950 single nucleotide polymorphisms (SNPs) were identified. Through the genome-wide comparison of SNP profiles between the resistant and the susceptible bulks constructed from F1 individuals derived from a cross between “Golden Delicious” and “Fuji,” the Rgls locus was identified on apple chromosome 15 between 2 and 5 Mb. In this region, eight SNP markers were validated using high resolution melting (HRM), and the fine genetic mapping of the eight markers was constructed. The Rgls locus was sandwiched by two flanking markers SNP4208 and SNP4257, with the recombination frequency of 0.97% (2/207). The marker SNP4236 co-segregated with Rgls. The physical size of the Rgls locus was estimated to be 49 kb. In this genetic interval, nine genes were predicted. Our study provides an effective method for rapid identification of genomic regions and development of the diagnostic markers for MAS. This strategy is potentially useful for other agronomic traits or plant species.