Quantitative trait locus (QTL) analysis of fruit-quality traits for mandarin breeding in Japan

The improvement of fruit quality is an important objective in citrus breeding. Using an F-1 segregating population from a cross between citrus cultivars 'Harehime' ('E647'-'Kiyomi' [Citrus unshiu Marcow. 'Miyagawa Wase' x Citrus sinensis (L.) Osbeck 'Trovita'] x 'Osceola'-a cultivar of clementine [Citrus clementina hort. ex Tanaka] x 'Orland' [Citrus paradisi Macfad. 'Duncan' x Citrus tangerina hort. ex Tanaka] x 'Miyagawa Wase') and 'Yoshida' ponkan (Citrus reticulata Blanco 'Yoshida'), a SNP-based genetic linkage map was constructed and quantitative trait locus (QTL) mapping of four fruit-quality traits (fruit weight, sugar content, peel puffing, and water rot) was performed. The constructed genetic linkage map of 'Harehime' consisted of 442 single nucleotide polymorphisms (SNPs) on 9 linkage groups (LGs) and covered 635.8 cM of the genome, while that of 'Yoshida' ponkan consisted of 332 SNPs on 9 LGs and covered 892.9 cM of its genome. We identified four QTLs associated with fruit weight, one QTL associated with sugar content, three QTLs associated with peel puffing, and one QTL associated with water rot. For these QTL regions, we estimated the haplotypes of the crossed parents and verified the founding cultivars that these QTLs were originated from and their inheritance in descendant cultivars using pedigree information. QTLs identified in this study provide useful information for marker-assisted breeding of citrus in Japan.