Mapping for Quantitative Trait Loci and Major Genes Associated with Fresh-cut Browning in Apple

Flesh browning is an important negative trait for quality preservation of fresh-cut fruits. To obtain a better understanding of the inheritance and genetic control of flesh browning in apple, the phenotype of a hybrid population derived from 'Jonathan' x 'Golden Delicious' was studied for 2 successive years. The inheritance of the flesh browning trait was analyzed by the frequency distribution of the phenotypes. Flesh browning-associated major genes were then mapped by screening genome-wide simple sequence repeat (SSR) markers. Flesh browning is inherited quantitatively and showed a clear bimodal frequency distribution, indicating that the segregation of major genes is involved in the variation. The segregation ratio of light and heavy browning was 7:1 in 2010, 2011, and 2010 + 2011, suggesting that the inheritance of the trait in apple involves three segregated loci of major genes. The heritability of the major gene effect was 72.14% and 72.76% in 2010 and 2011, respectively. SSR markers were screened from 600 pairs of SSR primers located on 17 apple linkage groups (LGs). The three major genes were mapped on LG10, 15, and 17 on the apple genome, respectively, by linkage analysis of flesh browning phenotypes and the genotypes of SSR markers. Two quantitative trait loci (QTLs) for flesh browning were mapped on LG15 of 'Jonathan' and LG17 of 'Golden Delicious', respectively, which are the same linkage groups that two major genes mapped on.