High-density genetic mapping identified a major locus for environmental sex expression in pumpkin (Cucurbita moschata Duch.)

Long-day length and high temperature inhibit sex expression in pumpkin (Cucurbita moschata Duch.), and therefore directly impact the production potential. In this study, female flowering patterns in photoperiod-insensitive (PPIS) and photoperiod-sensitive (PPS) germplasms differed significantly in a moderately long day and high temperature environment. However, both germplasms exhibited a similar response in short day with either low temperature or high temperature environment. Photoperiod sensitivity led to this difference in sex expression between the germplasms. For the traits of 1st female flowering node (FFFN) and number of female flowers (NFF), high-density linkage map construction and quantitative trait locus (QTL) mapping were performed using SLAF-seq technology and 162 F-2 individuals generated from PPIS and PPS. In total, 4 655 SLAFs were selected and mapped on 20 linkage groups (LGs). The total map length was 2 502.01 cM with an average interval distance of 0.75 cM. Major QTLs for both FFFN and NFF were detected on LG6 with intervals of 7.89 and 17.67 cM and PVE values of 30.5% and 22.9%, respectively. Further analyses of the major locus for FFFN revealed 73 protein-coding genes. Among them, 4 were related to sex expression, photoperiod flowering, and hormone response. An InDel (insertion and deletion) marker partially correlated with FFFN of the F-2 population was also developed. Our study identified the QTL for the sex expression response to environmental factors using the high-density linkage map. The identified candidate genes and markers will provide useful information about the molecular interaction between the environment and sex expression and for marker-assisted selection of pumpkin environment-insensitive resources.