Abstract
Low temperature is an important abiotic stress that negatively affects morphological growth and fruit development in melon (Cucumis melo L.). Chilling stress at the seedling stage causes seedling injury and poor stand establishment, prolonging vegetative growth and delaying fruit harvest. In this study, association mapping was performed for chilling tolerance at the seedling stage on an expanded melon core collection containing 212 diverse accessions by 272 SSRs and 27 CAPSs. Chilling tolerance of the melon seedlings was evaluated by calculating the chilling injury index (CII) in 2016 and 2017. Genetic diversity analysis of the whole accession panel presented two main groups, which corresponded to the two subspecies of C. melo, melo, and agrestis. Both the subspecies were sensitive to chilling but with agrestis being more tolerant. Genome-wide association study (GWAS) was conducted, respectively, on the whole panel and the two subspecies, totally detecting 51 loci that contributed to 74 marker-trait associations. Of these associations, 35 were detected in the whole panel, 21 in melo, and 18 in agrestis. About half of the associations identified in the two subspecies were also observed in the whole panel, and seven associations were shared by both the subspecies. CMCT505_Chr.1 was repeatedly detected in different populations with high phenotypic contribution and could be a key locus controlling chilling tolerance in C. melo. Nine loci were selected for evaluation of the phenotypic effects related to their alleles, which identified 11 elite alleles contributing to seedling chilling tolerance. Four such alleles existed in both the subspecies and six in either of the two subspecies. Analysis of 20 parental combinations for their allelic status and phenotypic values showed that the elite alleles collectively contributed to enhancement of the chilling tolerance. Tagging the loci responsible for chilling tolerance may simultaneously favor dissecting the complex adaptability traits and elevate the efficiency to improve chilling tolerance using marker-assisted selection in melon.
Highlights
Melon (Cucumis melo L.), an important horticultural crop, is planted widely in both tropical and temperate regions around the world
212 melon accessions were used for association mapping, which contained 189 diverse accessions and 23 accessions from USDA melon germplasm collection, and coved the major areas of origin of melons in the world (Supplementary Table S1)
20 hybrids were prepared with their parents chosen from the melon panel based on identification of the alleles related to chilling tolerance in the association mapping, and were used in the present study to examine the combination of potential elite alleles
Summary
Melon (Cucumis melo L.), an important horticultural crop, is planted widely in both tropical and temperate regions around the world This crop has abundant genetic diversity, especially for the fruit characters. Melon seedlings are more sensitive to low temperature than at other growth stages; in general, the seedlings stop growth at 10◦C–13◦C and display injury symptoms (e.g., leaf rolling, necrosis, and chlorosis) when the temperature falls below 8◦C (Lin et al, 1995). This leads to prolongation of the seedling stage delaying fruit harvest and listing. Developing new cultivars with enhanced chilling tolerance is helpful to solve this problem and has been a major focus in melon breeding programs (Luan et al, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
