Genetic mapping of quantitative trait loci controlling fruit size and shape in papaya

Papaya ( Carica papaya L.) is a pan-tropical tree that bears fruit exhibiting a wide range of size and shape. Depending on variety and environment, papaya fruit may weigh from 0.2 kg up to 10 kg. Papaya fruit shape is a sex-linked trait ranging from spherical to ovate, cylindrical or pyriform. An F2 mapping population, produced from a cross between the Thai variety Khaek Dum, bearing 1.2 kg, red-fleshed fruit, and variety 2H94, a Hawaii Solo type bearing a 0.2 kg, yellow-fleshed fruit, was used to identify quantitative trait loci (QTLs) that influence papaya fruit characters including weight, diameter, length and shape. Fruit phenotype data, collected from two subpopulations planted in successive growing seasons, showed striking differences by year indicating significant genotype × environment interactions. Fourteen QTL with phenotypic effects ranging from 5 to 23% were identified across six linkage groups (LGs) with clusters of two or more QTL on LGs 02, 03, 07 and 09. These loci contain homologs to the tomato fruit QTL ovate, sun and fw2.2 regulating fruit size and shape. The papaya fruit QTL provide a starting point for dissecting the genetic pathways leading to extreme fruit size and shape and may prove useful for papaya breeders attempting to tailor new varieties to specific consumer markets.