Abstract:

In the present study，a total of 192 representative melon germplasms were selected from the National Mid-term Genebank for Watermelon and Melon（Zhengzhou，China）and used as an association mapping population. The soluble solid content（SSC）in mature fruits of these melon accessions were measured in 2013，2014 and 2015，respectively. One hundred and four SSR markers distributed evenly across the melon chromosomes were adopted for association mapping with the fruit SSC of the germplasm pool，with the aim to explore the significant association loci and their elite alleles. The results showed that the 192 melon accessions possessed abundant fruit SSC variation and could be separated into two subgroups by the Bayesian model，the thin-skinned germplasm subgroup and the thick-skinned germplasm subgroup. Totally，16 SSR loci associated with the fruit SSC，which were distributed across the 10 chromosomes，were identified by the general linear model（GLM）and mixed linear model（MLM），with the maximum number of association loci across the chromosome 9. Of the loci detected，six loci expressed stably in two years and three loci in three years，and seven loci were in agreement with the previously published QTLs from linkage analysis. Eight SSR loci with high explanation of phenotypic variation and stable expression were selected from the comparative analysis，with the phenotypic effect of their elite alleles ranging from–5.87 to 4.06. The elite allele CMATN22-166 demonstrated the strongest positive effect with a mean of 2.56 and the typical carrier material Elizabeth，while CMCTTN166-157 had the strongest negative effect（mean =–5.16）with the carrier material PI163206，a local germplasm of India. Five elite alleles showed dominant frequencies，however，the rest three were low-frequency elite alleles（< 0.3）. The present results will be beneficial for further positional cloning of the genes related to quality characters and development of practical molecular markers in melon.

Key words: melon, soluble solid, simple-sequence repeat, association mapping, elite allele