中文摘要：

【目的】研究二倍体和同源四倍体西瓜幼苗NaCl胁迫后形态学指标差异和DNA甲基化变化情况,分析不同倍性西瓜幼苗之间耐盐差异,结合形态学指标从表观遗传学角度解释二倍体和四倍体抗逆性差异机制。【方法】以3组不同倍性（二倍体、四倍体）西瓜幼苗为研究对象,待长至三叶一心时,用含有0、100、200、300和400mmol·L-1 NaCl的1/2 Hoagland营养液处理西瓜幼苗,NaCl处理8 d之后,鉴定西瓜幼苗受到的盐害指数,并运用甲基化敏感扩增多态性（methylation sensitive amplified polymorphism,MSAP）技术,分析NaCl处理8 d之后二倍体和四倍体西瓜幼苗叶片基因组DNA甲基化水平和模式的变化。【结果】NaCl处理后,形态学指标比较发现,随着NaCl浓度的增加,三组西瓜幼苗的受伤害程度都随着增加,在不同的西瓜品种之间受伤害程度有差异,但是同一品种内同一NaCl浓度下,西瓜幼苗受伤害程度二倍体大于四倍体;从甲基化水平看,西瓜幼苗基因组DNA全甲基化率、半甲基化率、总甲基化率都随着NaCl浓度的增加而降低,同一NaCl浓度处理下甲基化率二倍体大于四倍体,二倍体和四倍体西瓜甲基化水平与其受伤害程度呈正相关;从甲基化模式来看,NaCl胁迫后DNA的去甲基化比率降低,超甲基化比率升高,并且其变化幅度是四倍体大于二倍体,不同倍性西瓜幼苗的甲基化模式与其受伤害程度呈负相关。【结论】NaCl胁迫后西瓜幼苗基因组DNA的甲基化状态发生了变化,并且这种变化与NaCl胁迫程度高度线性相关,西瓜幼苗通过降低甲基化率和降低去甲基化比率来应对NaCl胁迫,四倍体较二倍体有更低的甲基化比率和去甲基化比率,抗逆性四倍体强于二倍体。

英文摘要：

The morphological differences and DNA methylation changes of diploid and tetraploid watermelon seedlings after NaC1 stress were studied, combined with morphological indicators, this experiment aimed at explaining the resistance mechanisms between diploid and tetraploid watermelon seedlings from the perspective of epigenetics. [Method] Three groups of different ploidy （diploid, tetraploid） watermelon seedlings were used in this experiment, the watermelon seedlings were treated by using 1/2 Hoagland nutrient solution with NaC1 concentration at 0, 100, 200, 300, and 400 mmolL1 when the seedlings had three euphyllas, after 8 days of NaC1 treatment, the salt stress index of watermelon seedlings, the changes of methylation levels and patterns of the watermelon seedlings were analyzed by methylation-sensitive amplified polymorphism （methylation sensitive amplified polymorpbism, MSAP） technology. [Result] According the salt-damage morphological index comparison, it was found that after NaC1 treatment, with the increasing NaC1 concentration, the extent of injury of three groups watermelon seedlings also increased. There was a difference in degree of injury among three watermelon varieties, but at the same NaC1 concentration, the degree of injury in the diploid watermelon seedlings was greater than tetraploid which was in the same variety. From the methylation level perspective, the whole genomic DNA methylation rate, half rate of methylation, the total rate of methylation of watermelon seedlings decreased with the increase of NaC1 concentration, at the same NaCI concentration level, the methylation rate of diploid watermelon seedlings was bigger than the tetraploid ones, the methylation level was positively correlated with the degree of injury of the watermelon seedlings. From the methylation patterns, the DNA demethylation ratio decreased and the hypermethylation rate increased after NaC1 stress, at the same time, the magnitude of the changes in the tetraploid watermelon seedlings was greater than the diploid on