Abstract:

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 southeastern Gansu Province (100°-105° E, 30°-35° N), which are important water self-restraint regions. The genetic diversity of ten populations ofP. 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 H_e=0.096) of genetic variation within populations with values of P_P=29.41% - 41.18%, A_P=1.4 - 1.6 and H_ep=0.06 - 0.131; at the species level, the genetic diversity of P. asperata (P_s=41.18%, A_s=1.2, H_es=0.138) was lower than the mean value of long-lived woody angiosperm species (P_s=59.5%, A_s=2.10, H_es=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 F_is, 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 (F_st=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 (N_m=0.553 9), low level of inbreeding (mean F_is=0.005), and high level of outbreeding (F_is=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 (H_e) 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.

Key words: Picea asperata, Natural populations, Genetic diversity, Allozyme marker