粤西地区西南桦优良无性系早期选择

对粤西地区27个3 a 生西南桦（Betula alnoides）无性系进行调查测定，分析其生长和干形因子的差异，应用相对排序法进行综合评价，进而初步筛选优良无性系。结果表明，27个西南桦无性系间胸径、树高、冠幅和干形等级均呈极显著差异(P<0.01)，其均值分别为4.96 cm、4.32 m、2.58 m 和1.78；4个性状的变异系数为18.86%~40.88%，重复力为0.08~0.24。通过综合评价筛选出 FB2、A13、B1、Q2、Q4和 FB4共6个生长较为迅速、树干通直且较为圆满的西南桦优良无性系，其胸径、树高和冠幅均值分别比群体均值高7.62%、8.08%和5.50%，其干形等级值低18.87%，这些无性系可在粤西、桂东等地区推广应用。

Early Selection of Superior Clones of Betula alnoides in Western Guangdong

A total of 27 three-year-old clones of Betula alnoides planted in western Guangdong were studied. The growth performance and stem form of three-year-old B. alnoides were measured for preliminary selection of superior clones through the comprehensively evaluation by a relative ranking method. The results showed that there existed significant differences in diameter at breast height (DBH), height (H), crown diameter (CD) and stem form class (SF) among these clones (P<0.01), and their mean values were 4.96 cm, 4.32 m, 2.58 m and 1.78, respectively. The coefficients of variation ranged from 18.86% to 40.88%, and repeatability ranged from 0.08 to 0.24. The comprehensive evaluation based on a ranking system screened out 6 superior clones (FB2, A13, B1, Q2, Q4 and FB4) with relatively better performance in growth rate, stem straightness and fullness. Their DBH, H, CD and SF were improved by 7.62%, 8.08%, 5.50% and 18.87%, respectively, when compared with the total population. The selected clones could be promoted and applied in west of Guangdong and east of Guangxi.