甜瓜果实可溶性固形物含量的关联作图及优异等位变异发掘

Association Mapping of Soluble Solid Content in Melon Fruits and Exploration of the Elite Alleles

从国家西瓜甜瓜种质中期库(郑州)中抽取192份有代表性的甜瓜种质,于2013、2014和2015年分别测定成熟果实可溶性固形物含量(soluble solid content,SSC),采用在甜瓜染色体上均匀分布的104个SSR标记对SSC进行关联作图,发掘显著性关联位点及优异等位变异。结果表明,192份甜瓜种质果实的SSC变异明显,可划分为2个亚群,即薄皮种质亚群和厚皮种质亚群。应用一般线性模型(general linear model,GLM)和混合线性模型(mixed linear model,MLM),共检测到与SSC相关的16个位点,分布在10条染色体上,其中第9染色体的关联位点数最多。6个位点在2个年份稳定表达,3个位点在3个年份均稳定表达,7个位点与已报道的QTL定位结果一致。共检出8个表型解释率高且稳定表达的SSR位点,其等位变异的表型效应变幅为–5.87~4.06。等位变异CMATN22-166的增效作用最明显,平均效应为2.56,典型承载种质为伊丽莎白;CMCTTN166-157的减效作用最明显,平均效应为–5.16,典型承载种质为印度地方种质PI163206。5个优异等位变异是优势等位变异,3个是低频率(<0.3)的优异等位变异。

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.