不同类型甜瓜种质SSR遗传多样性及耐冷性评价

Genetic Diversity Analysis of Melon Germplasms Using SSR Markers and Tests for Chilling Tolerance

从国家西瓜甜瓜种质中期库(郑州)和美国农业部国家种质资源中心选取厚皮、薄皮和野生甜瓜种质共191份,利用在甜瓜染色体上均匀分布的43个SSR标记鉴定其基因型,评价其遗传多样性,并利用4℃恒温条件下种质幼苗的冷害指数和低温处理前后的叶肉组织超微结构变化评价不同类型种质的耐冷性。结果显示,SSR标记共检测到366个等位基因,平均8.512,平均观测杂合度和期望杂合度分别为0.074和0.704,平均多态性信息含量为0.668。UPGMA法将所有种质聚为4个类群,Ⅰ类群仅有2份印度野生种质,Ⅱ类群包含来自印度的34份野生和15份薄皮种质,Ⅲ类群含有地理分布广泛的51份厚皮和1份野生种质,IV类群由来自东亚的75份薄皮、7份厚皮和6份野生种质组成。Bayesian算法将所有种质分为3个亚群,主要对应厚皮、野生和薄皮3类种质。通过计算3类种质间的分化系数和雷氏距离,结果发现厚皮种质与薄皮种质间的分化最大,野生种质与薄皮或厚皮种质间的分化相对较小,不同类型种质多样性水平表现为:野生种质>厚皮种质>薄皮种质。3类种质幼苗的冷害指数趋向正态分布,薄皮种质的耐冷性要优于野生和厚皮种质。叶肉组织超微观察显示,薄皮种质蛤蟆酥5在低温处理前后的细胞超微结构变化不大,其耐冷性较强,而厚皮种质凤凰在低温处理后,叶绿体大量解体,细胞超微结构遭到破坏,其耐冷性较弱。

In order to investigate the genetic diversity of melon accessions,of 191 melon accessions including thick-skinned,thin-skinned,and wild types,which were collected from the National Mid-term Genebank for Watermelon and Melon(Zhengzhou,China)and USDA-ARS GRIN database,were analyzed with 43 chromosomally-distributed SSR markers.Furthermore,chilling tolerance was evaluated using the chillinginjury indices of melon seedlings under the constant temperature 4℃as well as the leaf-ultrastructure changes before and after the low-temperature treatment.Totally,366 alleles were detected by the SSR markers,with an average of 8.512 alleles per marker.Mean of observed and expected heterozygosity were 0.074 and 0.704,respectively,while mean of the polymorphism information index was 0.668.The method of UPGMA clustered all the accessions into four groups.Group Ⅰ had only two genetically diverse Indian accessions.Group Ⅱ included 34 wild accessions and 15 thin-skinned accessions,all of which were originated from India.Group Ⅲ comprised of 51 thick-skinned accessions and one wild accessions,which were collected from a wide geographic distribution.The remained 75 thin-skinned accessions,7 thick-skinned accessions and 6 wild accessions were clustered into group IV,most of which were from East Asia.Furthermore,the Bayesian algorithm assigned the whole accession panel into three subpopulations,mostly correlated to the three germplasm types,i.e.,thick-skinned,wild,and thin-skinned accessions.The coefficient of differentiation and Nei′genetic distance among the three germplasm types indicated the highest level of genetic differentiation(FST)between the thick-skinned and thin-skinned accessions,following by FST values between wild accessions and thick-skinned accessions or thin-skinned accessions.The rank of the diversity level among the germplasm types were:wild accessions>thick-skinned accessions>thinskinned accessions.The chilling-injury indices of the three germplasm types tended to follow normal distribution;the chilling tolerance of thin-skinned accessions was largely superior to that of wild or thick-skinned accessions.Leaf ultrastructure showed a slight change observed with the seedlings of the thin-skinned accession‘Hamasu5’,indicating a high level of chilling tolerance.In contrast,the thick-skinned accession‘Fenghuang’presented a heavy chloroplast destruction and an aggravated damage in cell ultrastructure,indicating a high sensitivity to chilling temperature.