Identification of markers linked to major gene loci involved in determination of fruit shape index of apples (Malus domestica)

Abstract

Fruit shape index (FSI) is one of the most important traits in apple. In this study, the inheritance of a FSI (ratio between height and diameter at the widest point of the fruit) was analysed in a hybrid population derived from ‘Jonathan’ × ‘Golden Delicious’ (Malus domestica Borkh) using frequency distribution and molecular marker analysis. A binary distribution pattern was observed which matched a 31:1 segregation ratio for small: large FSI scores. This ratio can be explained by the segregation of five independently inheriting single dose loci, whereby high FSI requires the simultaneous absence of all dominant alleles. The joined heritability of these major genes was estimated to be 75.00 and 75.51% in the year of 2008 and 2009, respectively. Bulked segregant analysis (BSA) on two subsets of 30 seedlings, 30 seedlings with large FSI and 30 seedlings with small FSI resulted in the discovery of four genomic regions associated with FSI. They are located at four linkage groups (10, 11, 12 and 13) at short distance of the SSR markers CH02c11, CH04a12, CH03c02 and GD147 respectively. One AFLP marker, M-CTA/E-AGG-0240, was also found. Our results indicated that five major genes involved in FSI determination segregated in this population and that the genotypes of the parental cultivars, ‘Jonathan’ and ‘Golden Delicious’, are putatively f10f10F11-1f11-1F11-2f11-2F12f12F13f13 and F10f10f11-1f11-1f11-2f11-2f12f12f13f13 respectively.