Development and characterization of a co-dominant molecular marker via sequence analysis of a genomic region containing the Female (F) locus in cucumber (Cucumis sativus L.)

Abstract

Cucumber is a typical monoecious having separate male and female flowers on the same plant, and sex expression in cucumber is mainly determined by three major genes: F/f, M/m and A/a. Gynoecy plays an important role in cucumber hybrid breeding, and the use of gynoecious lines as maternal parents ensures high productivity. This study aimed to identify a co-dominant marker linked to Female (F) locus to distinguish homozygous and heterozygous gynoecious lines for efficient selection of gynoecy in cucumber breeding. Firstly, we analyzed a 50-kb genomic sequence of five gynoecious and five monoecious inbred lines to detect the polymorphism linked to F locus. A pair of specific primers, Cs-BCAT-F/Cs-BCAT-R, based on an In/Del polymorphism at 3′-UTR of branched-chain amino acid transaminase (BCAT) gene was designed to examine the polymorphism in gynoecious and monoecious parents, their F1 hybrids and two F2 segregating populations. The PCR fragments amplified with Cs-BCAT-F/Cs-BCAT-R co-segregated with sexual phenotypes in the F2 populations, behaving as a co-dominant marker with two alleles: F (gynoecious) and f (monoecious). When we further verified the consistency of the co-dominant marker using additional 55 diverse inbred lines, it can explain ~90 % of accessions. Linkage analysis also showed that the gene which enhances the number of female flowers co-segregated with the co-dominant marker on the long arm of chromosome 6. This is the first report for the development of F locus-specific co-dominant marker which can distinguish perfectly homozygous and heterozygous gynoecious, and it could be used in marker-assisted selection in cucumber breeding.