云杉天然群体遗传多样性的等位酶变异

采用等位酶淀粉凝胶电泳和聚丙烯酰胺凝胶电泳技术对中国西部亚高山特有树种云杉(Picea asperata)10个天然群体的300个个体的遗传多样性和遗传分化进行研究。对8个酶系统17个酶位点(27个等位基因)的检测分析结果表明,10个位点为单态位点,云杉具有中等偏低的遗传变异水平。群体水平上的遗传多样性指标分别为:多态位点的百分率P_P=29.41%~41.18%,等位基因平均数A_P=1.4~1.6,平均期望杂合度H_ep=0.06~0.131;种级水平的遗传多样性指标分别为:P_s=41.18%,A_s=1.2,H_es=0.138。10个群体的群体水平的观测杂合度为0.094 3,期望杂合度为0.096 4;10个群体中,7个多态位点的单位点的观测杂合度(H_o)的均值为0.229(变幅为0.142 9~0.342 9),期望杂合度(H_e)的均值为0.234 1(变幅为0.160 8~0.317 3), 云杉天然群体间遗传分化度(F_ST)为0.311,云杉群体间变异占总变异的31.1%,基因流低(N_m=0.553 9),说明群体间的基因交流有限。异交率高(t=0.957),近交率低(F_is=0.005),这些研究结果表明:云杉群体间等位基因的频率分化显著,其它云杉属树种基因的渐渗、群体微生境差异和不同强度的选择压力可能是造成群体间分化显著的主要原因;Fdh-2-B基因与综合生态梯度值呈显著的负相关(r=-0.661 1^*),H_e与经度呈显著负相关(r=-0.683^*),云杉群体间的地理和遗传距离相关不显著。10个群体均含有绝大部分等位基因,且群体间分化很大,应加以重点保护和管理,作为云杉种质资源原地保存的基地和该树种进一步遗传改良的重要育种群体。

ALLOZYME VARIATION IN 10 NATURAL POPULATIONS OF PICEA ASPERATA

Picea asperata is an important tree for the production of pulp wood and timber and a prime reforestation species in western China. P. asperata occurs in the alpine and canyon regions of northwestern Sichuan Province and sout heastern Gansu Province (100°-105° E, 30°-35° N), which are important water self_restraint regions. The genetic diversity of ten populations of P. asperata  in the western part of China was assessed using allozyme analysis by horizontal sliceable starch gel electrophoresis. Seventeen loci (27 alleles) of 8 enzyme systems demonstrated relatively low levels (mean He=0.096) of genetic variation within populations with values of PP=29.41% - 41.18%, AP=1.4 - 1.6 and Hep= 0.06 - 0.131; at the species level, the genetic diversity of P. asperata ( Ps=4 1.18%, As=1.2, Hes=0.138) was lower than the mean value of long_ lived woody angiosperm species (Ps=59.5%, As=2.10, Hes=0.183 ). Genetic diversity is generally the result of long_term evolution. The low level of genetic variation present in P. asperata populations may be due to severe contractions in the area of distribution and population size during the last glacial period. Wrights F statistics analysis indicated that Fis, a measure of deviation from random mating within the 10 populations, was 0.005 suggesting deviation from Hardy_Weinberg equilibrium and a slight (homozygosity) excess in some populations. The higher level of differentiation (Fst=0.311) among populations than those of other long_lived woody plants may have resulted from factors such as habitat fragmentation, introgression from another species, variation in environmental conditions and differing selection pressure. Low level of gene flow (Nm=0.553 9), low level of inbreeding (mean Fis=0.005), and high level of outbreeding (Fis=0.005) could be caused by environmental deterioration and human disturbance, including over_harvesting. There were significantly negative correlations between Fdh_2_B gene and ecological gradient value (r=0.661 1*), as well as between expected heterozygosity (He) and longitude (r=0.683*). It was worth noting that the 10 populations harbored the majority of alleles and had higher genetic diversity suggesting that these populations in particular should be conserved in situ and form population used for tree improvement.