Allozyme variation and population genetic structure of Betula alnoides from Guangxi, China

Allozyme variation and population genetic structure of Betula alnoides Buch. Ham. ex D. Don in 11 natural populations from Guangxi Zhuang Autonomous Region, China, were investigated by starch gel electrophoresis. Variation at 15 loci from 10 enzyme systems was analyzed. Allozyme analysis revealed a high level of genetic variation in this species, with percentage of polymorphic loci (P-p), the average number of alleles per locus (A(p)), and the expected heterozygosity (Hep) being 55.2%, 2.0, and 0.204, respectively, which exceeds the average level among out-crossing wind-pollinated woody species at the population level. At the species level, P-s,A(s), and H-es were 60.0%, 2.67, and 0.206, respectively. The observed heterozygosity (Hop) was higher than Hep, indicating the existence of natural selection against homozygotes. The negative fixation index (F = -0.216) implied a significant excess of heterozygosity at the population level. Among-population differentiation (F-ST) accounted for 4.0% of the total variation. No significant correlation was detected between the genetic distance and geographic distance among populations. Extensive gene flow was inferred, based on the allozyme data (N-m = 6.000 from F-ST; N-m = 5.605 from the "private allele" method). The results demonstrated that the fragmentation status of B. alnoides had no remarkable effects on the population genetic structure of this species. Some populations are recommended for both in situ genetic conservation and germplasm collection for breeding programs.