Association Analysis of Six Yield-related Traits with SSR Markers in Melon(Cucumis melo L.) Landraces

Exploring the quantitative trait loci(QTL) of yield-related traits in melon(Cucumis melo L.) is helpful to the genetic improvement of melon yield. Total 221 melon landraces collected from various regions in China were used as experimental population in present study. The melon population was genotyped with 66 SSR markers that evenly distribute through the 12 melon chromosomes. On the basis of identification of population structure,genome-wide association study(GWAS) was applied to analyze the association between the SSR markers and the six yield-related traits,including fruit diameter,fruit length,thickness of fruit flesh,fresh weight of single fruit,1000-seed weigh,and yield per plot. The results showed that the melon landraces were rich in variation at phenotype and molecular level,with phenotypic Shannon's index of 1.69 and SSR polymorphic information content of 0.576,and this population with diverse accessions was suitable for GWAS. All the accessions were divided into three subgroups by the mathematical model-based cluster in Structure software; the information on the subgroup was used for the next GWAS. The GLM(general linear mode) program in TASSEL software was run to make regression analysis of the phenotypic data and molecular marker data. Twenty four markers were found to associate with the six traits,of which 8 marker associations were significantly different at P0.01. These markers distributed throughout the 11 linkage groups(LGs) besides LG 12,implying a complex genetic composition of the yield-related traits. Fourty seven marker-trait associations were detected herein,five for fruit diameter with an explanation of phenotypic variation(R2) range of 5.50% ~ 14.08%,six for fruit length with a R2range of 6.07%~14.22%,7 for thickness of fruit flesh with a R2range of 4.85%~11.22%,11 for fresh weight of single fruit with a R2range of 6.25%~14.22%,4 for 1000-seed weight with a R2range of 5.63%~10.50%,and 14 for yield per plot with a R2range of 47.4%~16.08%. As for some SSR markers,each co-associated with two or more traits. Positioning of some markers in association map were in agreement with the results of QTL mapping in reported genetic maps,whereas some markers were complementary to those located in the genetic maps. From the present study,the association loci mentioned above as well as their adjacent genome regions could contain numerous QTLs that influence melon yield and the related traits. The marker-trait association loci developed in present study will offer an important information for molecular improvement of melon yield.