以团头鲂"浦江1号"选育后期3个世代群体(F_7、F_8、F_9)为试验对象、其选育奠基群体(1985年淤泥湖野生群体)后代、淤泥湖野生群体(2007年)、梁子湖野生群体(2007年)为对照材料,通过ISSR标记技术分析,并通过部分样本的细胞色素b基因测序的补充验证,了解选育所产生的遗传变异及野生群体遗传结构现状.主要结果:(1)从100个ISSR引物中筛选出26个引物,扩增出清晰、可重复的条带共164条,多态性条带比例49.39%.细胞色素b基因在选育良种3个世代中只发现一种单倍型.(2)选育群体同选育奠基群体后代、野生群体间的遗传差异显著,如群体多态位点百分数,F_9(28.05%)比选育奠基群体后代(40.24%)减少了30.29%,比淤泥湖野生群体(41.46%)减少了32.34%.选育群体同淤泥湖野生群体间的遗传相似系数最小(0.935 0),距离最大(0.067 2),两两配对F_(ST)值最大(F_(ST)=0.305 72);UPGMA法构建系统进化树表明,选育群体同野生群体处于两个大分支,而在野生群体大支中,选育奠基群体后代与淤泥湖原种野生群体问配对F_(ST)值最小(F_(ST)=0.050 45).(3)选育群体F_7、F_8、F_9各世代间遗传分化虽弱(低GST0.141 7值,高Nm 3.027 9值),但多态位点百分数、位点基因平均多样性、Nei氏基因多样性、群体内Shannon多样性指数等遗传参数仍然都呈现随选育世代数的累进而降低的趋势.(4)ISSR比细胞色素b基因更适合近缘种的相关关系研究.(5)经过二十多年9代的选育,相对于野生群体,团头鲂"浦江1号"良种已产生了明显的遗传分化,性状已相当稳定,但离选育极限尚有一定距离,今后应在继续监测其遗传结构变化的基础上,进一步挖掘选育潜力,同时要避免种质混杂、近交衰退及瓶颈效应等的发生.%Inter-simple sequence repeat (ISSR) analysis was performed in order to evaluate three successively selected populations ( F_/F_8/F_9 of Pujiang No. 1 breeding improved variety), two wild populations (Liangzi Lake/Yuni Lake of 2007) and one hatchery population (Base group, offspring of Yuni lake of 1985 ) of blunt snout bream (Megalobrama amblycephala). The sequence analysis of mitochondrial DNA cytchrome gene was also used to evaluate the effectiveness of ISSR analysis. Main results: (1) Among 100 ISSR primers, 26 could produce 164 clear and repeatable bands, of which 81 bands appeared to be polymorphic(49.39% ). The sequencing analysis of the cyt b gene presents that three selected generations (F_,F_8,F_9) of Pujiang No. 1 possess the same haplotype. (2) There is a high genetic differentiation between wild/base and selected populations. Compared to Yuni Lake and base population, the percentage of polymorphic loci of F_9 generation decreased by 32. 34% and 30. 29% respectively. Genetic distance (0.067 2) ,pairwise F values(0.305 72)were the highest between F_9 generation and Yuni lake population. Based on the UPGMA dendrogram: the selected populations (F_7, F_8, F_9) are genetically distinct they were placed in a relatively derived position as the sister branch to a branch containing wild and base populations, it also shows the closest relationship between Yuni Lake and base population. (3) The low G_(ST) value (0.141 7) combined with the high N_m value(3.027 9) contributed to lower degree of genetic divergence among selected populations (F_7, F_8, F_9); The percentage of polymorphic loci/Average gene diversity over loci/Neis (1973) gene diversity and Shannon genetic diversity show a tendency that it has been decreased generation by generation. (4) The ISSR technique used was confirmed to be more sensitive than cyt b sequence analysis for the study of closely related populations. (5)The authors acknowledged that,through over 20 years and 9 generations selection, compared with the wild population, Pujiang No. 1 variety exhibits a significant differentiation from the wild population in genetics, and shows a rather high stability in improved trails, but there is still some distance from the plateau of selection. In the future, based on the monitoring of changes in genetic structure, potential for selection should be tapped further and attention should be paid to the possible mix in genetics, inbreeding and genetic bottleneck .
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