以采自广西区11个西南桦(Betula alnoides)天然居群的种子培育出的幼苗为材料，取其嫩叶开展21种酶系统的水平切片淀粉凝胶电泳实验，运用作者改进的Tris-马来酸提取缓冲液 (含30%PVP 40 000和1%2-巯基乙醇)，筛选出AMP(氨基肽酶Aminopeptidase)、FBA(果糖二磷酸酶Fructose-bisphosphate aldolase)、GDH(谷氨酸脱氢酶Glutamate dehydrogenase)、G6PD(6-磷酸葡萄糖脱氢酶Glucose-6-phosphate dehydrogenase)、IDH(异柠檬酸脱氢酶Isocitrate dehydrogenase)、MDH(苹果酸脱氢酶Malate dehydrogenase)、PGD(6-磷酸葡萄糖酸脱氢酶Phosphogluconate dehydrogenase)、PGI(磷酸葡萄糖异构酶Phosphoglucoisomerase)、PGM(磷酸葡萄糖变位酶Phosphoglucomutase)和SKD(莽草酸脱氢酶Shikimate dehydrogenase)等10种酶，获得了清晰且可重复的酶谱。通过谱带遗传分析确定了15个位点，其中有6个单态位点，9个多态位点 (0.95标准)，具40个等位基因。在居群水平上，西南桦的多态位点百分数 (P) 为55.2%，平均每个位点的等位基因数 (A) 为2.00，平均预期杂合度 (He) 为0.204。均超过Hamrick (1992)等提出的远交风媒木本植物的平均值(53.0%，184%和0154)，表明西南桦的遗传变异水平高。在11个西南桦居群内，实际杂合度 (Ho)均高于预期杂合度，出现杂合子过量，可能存在利于杂合子的自然选择。西南桦遗传多样性与地理位置相关不显著。居群2 (靖西地州)、5 (平果海城)、9 (田林者苗) 包含绝大部分的等位基因，而且具较高的遗传多样性，应加以保护和管理，作为其基因资源就地保存的基地。本研究解决了以西南桦嫩叶为材料进行等位酶分析的关键技术，为进一步开展西南桦乃至桦木属树种的遗传结构和遗传多样性等提供了技术基础；同时掌握了西南桦天然居群的遗传多样性现状，为其有效保护和合理经营以及西南桦的遗传改良提供了理论依据。
Betula alnoides is a valuable tree species in tropical and warm sub-tropical areas in South-east Asia and China. Its natural populations have become increasingly fragmented due to over-harvesting for local economic development in Guangxi, China during the last decade. Thus conservation of its genetic resources is of urgent need for future genetic improvement programs and sustainable management. Here, the allozyme diversity of Betula alnoides was analyzed by starch gel electrophoresis with improved Tris-maleate extraction buffer. Young leaves were collected from seedlings grown by seeds from 11 natural populations in Guangxi, China. Of the 21 enzymes tested, 10 (AMP, FBA, GDH, G6PD, IDH, MDH, PGD, PGI, PGM and SKD) could be consistently resolved and scored. Among 15 interpretable loci there were 9 polymorphic loci (0.95 criterion); the remaining 6 loci were monomorphic. High genetic variability was quantified by three indices: percentage of polymorphic loci (P), mean number of alleles per locus (A) and mean expected heterozygosity (He). The observed values of these indices were 55.2%, 2.00 and 0.204 respectively, all of which were higher than the averages of outcrossing wind-pollinated woody species (53.0%, 1.84 and 0.154, summarized by Hamrick et al., 1989). Ho was always higher than He in the 11 populations, indicating an excess of heterozygotes, which perhaps resulted from a higher probability of survival for heterozygous individuals. No significant correlation was detected between the genetic diversity and geographic variables of these populations. It is worth noting that populations 2 (Dizhou, Jingxi County), 5 (Haicheng, Pingguo County) and 9 (Zhemiao, Tianlin County) should be selected and managed as in-situ conservation localities, because they contain a majority of alleles and high levels of genetic diversity. The method and findings in this study could be applied in further studies on the genetic structure, diversity and genetic improvement of this species and other species of the genus Betula. Betula alnoides is a valuable tree species in tropical and warm sub-tropical areas in South-east Asia and China. Its natural populations have become increasingly fragmented due to over-harvesting for local economic development in Guangxi, China during the last decade. Thus conservation of its genetic resources is of urgent need for future genetic improvement programs and sustainable management. Here, the allozyme diversity of Betula alnoides was analyzed by starch gel electrophoresis with improved Tris-maleate extraction buffer. Young leaves were collected from seedlings grown by seeds from 11 natural populations in Guangxi, China. Of the 21 enzymes tested, 10 (AMP, FBA, GDH, G6PD, IDH, MDH, PGD, PGI, PGM and SKD) could be consistently resolved and scored. Among 15 interpretable loci there were 9 polymorphic loci (0.95 criterion); the remaining 6 loci were monomorphic. High genetic variability was quantified by three indices: percentage of polymorphic loci (P), mean number of alleles per locus (A) and mean expected heterozygosity (He). The observed values of these indices were 55.2%, 2.00 and 0.204 respectively, all of which were higher than the averages of outcrossing wind-pollinated woody species (53.0%, 1.84 and 0.154, summarized by Hamrick et al., 1989). Ho was always higher than He in the 11 populations, indicating an excess of heterozygotes, which perhaps resulted from a higher probability of survival for heterozygous individuals. No significant correlation was detected between the genetic diversity and geographic variables of these populations. It is worth noting that populations 2 (Dizhou, Jingxi County), 5 (Haicheng, Pingguo County) and 9 (Zhemiao, Tianlin County) should be selected and managed as in-situ conservation localities, because they contain a majority of alleles and high levels of genetic diversity. The method and findings in this study could be applied in further studies on the genetic structure, diversity and genetic improvement of this species and other species of the genus Betula.