Dissecting the Genetic Architecture of Melon Chilling Tolerance at the Seedling Stage by Association Mapping and Identification of the Elite Alleles

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.

Identification and Characterization of Stress-Responsive TAS3-Derived TasiRNAs in Melon

“…Considering that equivalent pathways might be regulated by ARFs in melon, it is reasonable to assume that the down-regulation of the TAS3-derived tasiRNA observed in cold-exposed and HSVd-infected plants might be related to the developmental alterations observed in plants growing under these adverse environmental conditions, mainly characterized by delayed growth (Hataya et al 2017, Hou et al 2018. However, we cannot exclude the possibility that changes in the ARF levels observed in cold exposed and HSVd-infected plants may be also modulated, at least in part, by and stress-related increasing in its transcription level, resembling the previously observed in divers plant species such as rice (Jain and Khurana, 2009), sorghum (Wang et al, 2010), banana (Hu et al, 2015) and pepper .…”

Mapping a Partial Andromonoecy Locus in Citrullus lanatus Using BSA-Seq and GWAS Approaches

“…It also identified two SNPs on chromosome 1 as being responsible for the PA phenotype. GWAS was used to map other important agronomic traits in watermelon, melon and cucumber ( Nimmakayala et al, 2016 ; Yagcioglu et al, 2016 ; Dou et al, 2018a ; Dou et al, 2018b ; Hou et al, 2018 ; Wang et al, 2018 ; Bo et al, 2019b ; Bo et al, 2019a ; Oren et al, 2019 ). The major sex-determining gene for monoecy/andromonoecy in melon ( CmACS7 ) was also successfully detected using the GWAS approach ( Gur et al, 2017 ; Zhang H. et al, 2019 ), but so far no other andromonoecy locus had been found in cucurbits.…”

Identification of candidate genes that regulate the trade-off between seedling cold tolerance and fruit quality in melon (Cucumis melo L.)

“…Two-leaf seedlings were used in the cold treatment experiments. Seedlings with developmental uniformity were treated in a climatic chamber at 4°C for 48 h, followed by recovery at normal conditions for 72 h. The chilling injury class was then determined by scoring the phenotype of the first true leaf, and the chilling injury index (CII) was calculated according to Hou et al [ 18 ], although the number of injury classes was increased from five to nine. Three biological replicates were performed for CII and each replicate contained 15 individuals.…”

“…Compared with model plants such as Arabidopsis thaliana , rice, and tomato, research into cold tolerance in melon lags behind. CMCT505_Chr.1 was identified as a key locus that controls cold tolerance in melon in a genome-wide association study (GWAS), but it was not genetically dissected [ 18 ]. At present, no QTL or gene related to low temperature tolerance has been cloned using forward genetics in melon.…”