用EST-SSR标记分析中国北部和中部地区天蓝苜蓿的遗传多样性和遗传结构

Genetic structure and diversity of Medicago lupulina populations in northern and central China based on EST-SSRs markers

天蓝苜蓿(Medicago lupulina)隶属于苜蓿属,是一年生或越年生、广布的草本植物。通常认为它是自交种,但也有些研究报道它具有异交或者混合交配的繁育系统。为了了解它的居群遗传变异、基因流、繁育方式及其遗传背景,我们用9个EST-SSR标记分析了中国新疆、内蒙古、甘肃、北京、山西、陕西、湖北7个省区的17个天蓝苜蓿野生居群。结果表明:(1)EST-SSR的多态位点百分率(PPL)为71.9%;每个SSR位点的等位基因数(A)为4-11(平均为7.333);遗传多样性(HE)最高的居群是新疆那拉提(0.388),最低的为陕西西安(0.042)。自交率达93.8%。(2)居群间的遗传分化水平高(FST=0.528;RST=0.499),AMOVA分析结果显示遗传变异主要存在于居群间,占总变异的59.02%。(3)Mantel检验发现遗传距离和地理距离有显著的相关性(r=0.4141,P≤0.0003)。根据Nei's遗传距离(Da)得出的Neighbor-joining树显示,地理距离近的居群聚在一起,这进一步验证了Mantel检验的结果。由此推测,天蓝苜蓿中等水平的遗传多样性和高度的居群间遗传分化主要受它的自交特性和分布方式影响。上述结果有助于初步了解天蓝苜蓿的种群动态和遗传结构,同时对苜蓿属种质资源的保护和遗传育种有重要意义。

Medicago lupulina is an annual or short-perennial and widespread herbaceous plant. It is generally considered a selfing species with a strong self-compatibility system, but a shift in mating system towards outcrossing or mix-mating has been reported. To estimate genetic variation, gene flow, mating system and genetic background of M. lupulina, we characterized 354 individuals from 17 wild populations from northern and central China using nine EST-SSRs markers. We found that： （1） EST-SSRs markers had a high percentage of polymorphic loci （PPL = 71.9%） and 4-11 alleles per loci. The Xinjiang-Nalati population had the highest level of genetic diversity （HE= 0.388）, whereas the Shaanxi-Xi＇an population had the lowest （HE= 0.042）. Selfing rate was 93.8 %. （2） Genetic differentiation was high among populations （FST= 0.528; RST= 0.499）. Of the total genetic variation, 59.02% was found among populations. （3） Mantel test revealed that genetic distance and geographic distance were positively correlated （r = 0.4141, P 〈 0.0003）. Neighborjoining trees based on Nei＇s genetic distance （Da） showed that neighboring populations clustered into the same clade, which was consistent with results of Mantel test. Our results indicated that the genetic structure ofM. lupulina populations have been strongly affected by dispersal patterns and a strategy of inbreeding.