QTL mapping of domestication and diversifying selection related traits in round-fruited semi-wild Xishuangbanna cucumber (Cucumis sativus L. var. xishuangbannanesis)

Abstract

QTL analysis revealed 11 QTL underlying flowering time and fruit size variation in the semi-wild Xishuangbanna cucumber, of which, FT6.2 and FS5.2 played the most important roles in determining photoperiod-dependent flowering time and round-fruit shape, respectively. Flowering time and fruit size are two important traits in domestication and diversifying selection in cucumber, but their genetic basis is not well understood. Here we reported QTL mapping results on flowering time and fruit size with F and F segregating populations derived from the cross between WI7200, a small fruited, early flowering primitive cultivated cucumber and WI7167, a round-fruited, later flowering semi-wild Xishuangbanna (XIS) cucumber. A linkage map with 267 microsatellite marker loci was developed with 138 F plants. Phenotypic data of male and female flowering time, fruit length and diameter and three other traits (mature fruit weight and number, and seedling hypocotyl length) were collected in multiple environments. Three flowering time QTL, FT1.1, FT5.1 and FT6.2 were identified, in which FT6.2 played the most important role in conferring less photoperiod sensitive early flowering during domestication whereas FT1.1 seemed more influential in regulating flowering time within the cultivated cucumber. Eight consensus fruit size QTL distributed in 7 chromosomes were detected, each of which contributed to both longitudinal and radial growth in cucumber fruit development. Among them, FS5.2 on chromosome 5 exhibited the largest effect on the determination of round fruit shape that was characteristic of the WI7167 XIS cucumber. Possible roles of these flowering time and fruit size QTL in domestication of cucumber and crop evolution of the semi-wild XIS cucumber, as well as the genetic basis of round fruit shape in cucumber are discussed.

FLOWERING LOCUS T Improves Cucumber Adaptation to Higher Latitudes

“…We propose that there are loci other than CsFT that determine flowering time in these accessions. This is consistent with previous studies reporting cucumber flowering time quantitative trait loci on chromosome 1, chromosome 5, and chromosome 6 (Dijkhuizen and Staub, 2002;Fazio et al, 2003;Weng et al, 2010;Bo et al, 2015;Pan et al, 2017).…”

The USDA cucumber (Cucumis sativus L.) collection: genetic diversity, population structure, genome-wide association studies, and core collection development

“…More than 100 putative selective sweeps appear to be associated with domestication, including extended linkage disequilibrium in regions surrounding loci associated with key fruit traits such as size and bitterness. Results of the genomic analyses, including assignment of a basal role of the Indian group and separation of the orange-endocarp Xishuangbanna group, complement prior genetic and morphological assessments 12 – 16 . These analyses have allowed for evolutionary insight into the relationships and domestication trajectories among cucumber accessions.…”

“… 56 ), and on chromosomes 1, 5, and 6 in a cross between American pickling cucumber and semi-wild var. Xishuangbanna 16 . There appears to be potential overlap among the identified QTL in those studies and the current GWAS.…”

LITTLELEAF (LL) encodes a WD40 repeat domain‐containing protein associated with organ size variation in cucumber

“…in cucumber, none was localized to the map location of ll (e.g. Yuan et al ., ; Qi et al ., ; Shi et al ., ; Bo et al ., ; Weng et al ., ; Pan et al ., ,b). These data are consistent with spontaneous mutation of the ll allele in H19, which affects the size of multiple organs and conceivably plays a more fundamental role in plant growth and development.…”