Quantitative trait loci for sex ratio in monoecious bitter gourd (Momordica charantia)

Abstract

Sex ratio (male or female flower frequency per plant) is an important trait of monoecious bitter gourds because it directly influences fruit yield. Quantitative trait loci (QTL) for the sex ratio were explored in F2 populations derived from the gynoecious OHB61-5 and monoecious OHB95-1A using both QTL mapping and QTL-seq methods. Female flower frequency data was used as the phenotype data, along with 1,036 bin-marker genotypes, and linkage maps from previous studies to detect sex ratio QTL. For QTL-seq, after the strong effect of the gynoecious locus was masked by marker-assisted selection of its heterozygotes, F2 plants showing higher- or lower-female flower frequency were selected and employed for making bulked samples. Three QTL were found on chromosomes 2 and 5 by QTL-seq, and only the qFR5-2 on chromosome 5 was identified by both QTL mapping and QTL-seq analyses. Focusing on the expressed genes with non-synonymous variations between parental lines in qFR5-2, 16 genes were nominated as candidate causal genes. Four of these encoded L-type lectin receptor kinase (LecRK), and amino acid substitutions in the conserved lectin or kinase domain were observed in three LecRKs between parental lines. Markers or genes for these sex ratio QTL will contribute to the development of bitter gourd inbred lines useful for stable production of fruits.