Volume 37 Issue 4
Jul.  2020
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YE Shuyuan, DONG Leiming, DONG Ang, YU Weiwu, DAI Wensheng, ZENG Yanru. Estimation of genetic parameters for juvenile growth of half-sib seedlings of Torreya grandis[J]. Journal of Zhejiang A&F University, 2020, 37(4): 817-822. doi: 10.11833/j.issn.2095-0756.20190542
Citation: YE Shuyuan, DONG Leiming, DONG Ang, YU Weiwu, DAI Wensheng, ZENG Yanru. Estimation of genetic parameters for juvenile growth of half-sib seedlings of Torreya grandis[J]. Journal of Zhejiang A&F University, 2020, 37(4): 817-822. doi: 10.11833/j.issn.2095-0756.20190542

Estimation of genetic parameters for juvenile growth of half-sib seedlings of Torreya grandis

doi: 10.11833/j.issn.2095-0756.20190542
  • Received Date: 2019-09-17
  • Rev Recd Date: 2020-03-14
  • Available Online: 2020-07-21
  • Publish Date: 2020-07-21
  •   Objective   To provide rationale for the selection and breeding of natural superior individuals of Torreya grandis, this research is intended to study the inheritance of the growth traits of T. grandis seedlings which are generally used as the rootstock for grafting scions from T. grandis ‘Merrillii’ in production.   Method   With half-sib seedlings of T. grandis openly pollinated in the natural forests as a material, the height, basal diameter and number of branches were measured for two consecutive years while the relevant genetic parameters were fitted and estimated employing conventional linear mixed model (LMM) and generalized linear mixed model (GLMM) so as to calculate the genetic and phenotypic correlation coefficients.   Result   The coefficient of variation of seedling height was greater than that of basal diameter and decreased with the seedling age. Every growth trait parameter displayed a very significant difference among families (P<0.01) and a relatively high heritability. The heritability of one-year-old seedlings for each parameter was higher than that of two-year-old seedlings and the genetic correlation was greater than that of phenotypic correlation. In terms of genetic gain, the seedling height was bigger than the basal diameter and the number of branches, and the genetic gain of the annual shoot was the highest. The correlation analysis of growth phenotypic traits showed that there was a significant correlation between genotype and phenotype of the same batch seedlings in all the parameters except the number of branches.   Conclusion  Natural T. grandis populations have displayed the great potential for selection and breeding in growth traits. Seed-bearing trees could be selected based on the height of one-year-old seedlings for the purpose of stock cultivation. [Ch, 3 tab. 24 ref.]
  • [1] ZHOU Jiajun, HU Hengkang, GONG Li, GAN Ange, YU Weiwu, WU Jiasheng, HUANG Jianqin, ZHANG Qixiang.  Agrobacterium tumefaciens-mediated genetic transformation system of Torreya grandis ‘Merrillii’ immature embryos . Journal of Zhejiang A&F University, 2022, 39(1): 13-21. doi: 10.11833/j.issn.2095-0756.20210196
    [2] ZHENG Liuhui, ZHAN Liyun, HOU Yu, YU Weiwu, ZENG Yanru, DAI Wensheng.  SSR analysis of genetic diversity of male Torreya grandis . Journal of Zhejiang A&F University, 2022, 39(2): 329-337. doi: 10.11833/j.issn.2095-0756.20210279
    [3] YUAN Ya’nan, LI Zhengcai, WANG Bin, ZHANG Yujie, HUANG Shengyi.  Stoichiometric characteristics of soil C, N and P in Torreya grandis stands of different ages . Journal of Zhejiang A&F University, 2021, 38(5): 1050-1057. doi: 10.11833/j.issn.2095-0756.20200761
    [4] QIAN Yuting, XUE Xiaofeng, ZENG Yanru, CHEN Wenchong, YE Xiaoming, YU Weiwu, DAI Wensheng.  Leaf structure and chlorophyll content in Torreya grandis 'Merrillii' with Nalepella abiesis infestation . Journal of Zhejiang A&F University, 2020, 37(2): 296-302. doi: 10.11833/j.issn.2095-0756.2020.02.014
    [5] ZHAN Liyun, LIU Lian, ZENG Yanru, YU Weiwu, DAI Wensheng.  Phenotypic diversity of male cones and the selection of superior plants among male populations in Torreya grandis . Journal of Zhejiang A&F University, 2020, 37(6): 1120-1127. doi: 10.11833/j.issn.2095-0756.20190676
    [6] JIN Houding, YU Weiwu, ZENG Yanru, XIANG Meiyun, DAI Wensheng, DANG Wanyu.  Cutting-based propagation in Torreya grandis 'Merrillii' . Journal of Zhejiang A&F University, 2017, 34(1): 185-191. doi: 10.11833/j.issn.2095-0756.2017.01.025
    [7] NING Ke, SHEN Yueqin, ZHU Zhen, XU Cuixia, HUANG Jiangqin.  Household's production behavior of featured economic forest based on Zhejiang Torreya grandis ‘Merrillii’ . Journal of Zhejiang A&F University, 2016, 33(4): 673-679. doi: 10.11833/j.issn.2095-0756.2016.04.017
    [8] ZENG Songwei, YU Weiwu, JI Changying, YE Bangxuan, XIAO Qinglai.  A peeling machine for Torreya grandis ‘Merrillii’ nuts . Journal of Zhejiang A&F University, 2015, 32(1): 133-139. doi: 10.11833/j.issn.2095-0756.2015.01.020
    [9] LIU Mengmeng, ZENG Yanru, JIANG Jianbin, HAN Jiong, YU Weiwu.  Mineral elements in leaves and seeds of Torreya grandis ‘Merrillii’ during seed development . Journal of Zhejiang A&F University, 2014, 31(5): 724-729. doi: 10.11833/j.issn.2095-0756.2014.05.010
    [10] DONG Leiming, ZENG Yanru, WU Yufen, HUANG Yinzhi, WU Dong, DAI Wensheng.  Variations in phenotypic traits and chemical compositions of seeds from a natural population in Torreya grandis . Journal of Zhejiang A&F University, 2014, 31(2): 224-230. doi: 10.11833/j.issn.2095-0756.2014.02.010
    [11] WU Lianhai, WU Liming, NI Rongxin, YAN Fuhua.  Economic benefits of Torreya grandis ‘Merrillii’ plantings . Journal of Zhejiang A&F University, 2013, 30(2): 299-303. doi: 10.11833/j.issn.2095-0756.2013.02.023
    [12] DONG Lei-ming, SHEN Deng-feng, YU Wei-wu, ZENG Yan-ru, WU Zhi-min, DAI Wen-sheng.  Trait variations of male Torreya grandis trees . Journal of Zhejiang A&F University, 2012, 29(5): 715-721. doi: 10.11833/j.issn.2095-0756.2012.05.013
    [13] SHEN Deng-feng, ZENG Yan-ru, YU Wei-wu, LI Zhang-ju, ZHANG Min, LI Yuan-chun, HUA Jia-qi, YU Shi-qun.  Collection of Torreya grandis germplasm and analysis of seeds’ physico-chemical characteristics . Journal of Zhejiang A&F University, 2011, 28(5): 747-752. doi: 10.11833/j.issn.2095-0756.2011.05.010
    [14] YE Sheng-yue, CHEN Gang, ZHANG Hui, LIU Jian-jie, ZENG Yan-ru, WU Hui-min.  Optimization of an ISSR-PCR system and primer screening for Torreya grandis ‘Merrillii’ . Journal of Zhejiang A&F University, 2010, 27(1): 87-92. doi: 10.11833/j.issn.2095-0756.2010.01.014
    [15] LIANG Dan, ZHOU Qin, SHU Yan, ZENG Yan-ru, YU Wei-wu.  AFLP-based sexual identification in Torreya grandis . Journal of Zhejiang A&F University, 2009, 26(1): 63-67.
    [16] WANG Xiao-ming, WANG Ke, QIN Sui-chu, JIANG Yu-gen.  Review of research on favorable environmental factors of Torreya grandis ‘Merrillii’ . Journal of Zhejiang A&F University, 2008, 25(3): 382-386.
    [17] CHENG Xiao_jian, LI Zhang_ju, YUWei-wu, DAI Wen-sheng, FUQing-gong.  Distribution and ecological characteristics of Torreya grandis in China . Journal of Zhejiang A&F University, 2007, 24(4): 383-388.
    [18] DAI Wen-sheng, LI Zhang-ju, CHENG Xiao-jian, YU Wei-wu, FU Qing-gong, CHEN Qin-juan.  Development future and strategies of production of Torreya grandis 'Merrillii' in Hangzhou . Journal of Zhejiang A&F University, 2006, 23(3): 334-337.
    [19] LI Zhang-ju, CHENGXiao-jian, DAI Wen-sheng, JING Bao-hua, WANG An-guo.  History and status and development of Torreya grandis in Zhejiang Province . Journal of Zhejiang A&F University, 2004, 21(4): 471-474.
    [20] MENG Hong-fei, JIN Guo-long, WENG Zhong-yuan.  Investigation on resource of ancient Torreya grandis trees in Zhuji City , China . Journal of Zhejiang A&F University, 2003, 20(2): 134-136.
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Estimation of genetic parameters for juvenile growth of half-sib seedlings of Torreya grandis

doi: 10.11833/j.issn.2095-0756.20190542

Abstract:   Objective   To provide rationale for the selection and breeding of natural superior individuals of Torreya grandis, this research is intended to study the inheritance of the growth traits of T. grandis seedlings which are generally used as the rootstock for grafting scions from T. grandis ‘Merrillii’ in production.   Method   With half-sib seedlings of T. grandis openly pollinated in the natural forests as a material, the height, basal diameter and number of branches were measured for two consecutive years while the relevant genetic parameters were fitted and estimated employing conventional linear mixed model (LMM) and generalized linear mixed model (GLMM) so as to calculate the genetic and phenotypic correlation coefficients.   Result   The coefficient of variation of seedling height was greater than that of basal diameter and decreased with the seedling age. Every growth trait parameter displayed a very significant difference among families (P<0.01) and a relatively high heritability. The heritability of one-year-old seedlings for each parameter was higher than that of two-year-old seedlings and the genetic correlation was greater than that of phenotypic correlation. In terms of genetic gain, the seedling height was bigger than the basal diameter and the number of branches, and the genetic gain of the annual shoot was the highest. The correlation analysis of growth phenotypic traits showed that there was a significant correlation between genotype and phenotype of the same batch seedlings in all the parameters except the number of branches.   Conclusion  Natural T. grandis populations have displayed the great potential for selection and breeding in growth traits. Seed-bearing trees could be selected based on the height of one-year-old seedlings for the purpose of stock cultivation. [Ch, 3 tab. 24 ref.]

YE Shuyuan, DONG Leiming, DONG Ang, YU Weiwu, DAI Wensheng, ZENG Yanru. Estimation of genetic parameters for juvenile growth of half-sib seedlings of Torreya grandis[J]. Journal of Zhejiang A&F University, 2020, 37(4): 817-822. doi: 10.11833/j.issn.2095-0756.20190542
Citation: YE Shuyuan, DONG Leiming, DONG Ang, YU Weiwu, DAI Wensheng, ZENG Yanru. Estimation of genetic parameters for juvenile growth of half-sib seedlings of Torreya grandis[J]. Journal of Zhejiang A&F University, 2020, 37(4): 817-822. doi: 10.11833/j.issn.2095-0756.20190542
  • 榧树Torreya grandis多雌雄异株,因天然杂交而群体内遗传多样性丰富[1]。此外,榧树分布范围广,地理环境复杂,极大地增加了榧树种内的性状变异[1-3]。丰富的自然变异为榧树优良种质的选育提供了物质基础。迄今为止,唯一进行人工大面积栽培的香榧T. grandis ‘Merrillii’是榧树优良变异类型经无性繁殖培育而成的优良栽培类型[4-5]。除香榧外,近年来在榧树中发现了许多优良自然变异类型,包括以种子生产为目的种质[6]及种子营养成分含量高[7]或生长性状优良的种质[8],一些优株的综合性状品质甚至超过香榧[6-7]。嫁接是经济树种无性繁殖的方式之一,可以保持嫁接品种的优良性状。生产上榧树优良种质的扩繁以嫁接繁殖为主,而嫁接用的砧木均以榧树种子实生繁殖而成。目前生产上提倡香榧大苗造林,培养的嫁接苗至少为2+2(砧木培养2 a后嫁接,嫁接苗至少再培养2 a才能造林)。研究表明:砧木显著影响接穗生长势[9]、嫁接植株的抗旱性[10]、果实化学成分的积累[11]。香榧嫁接时发现,直径越粗的砧苗往往根系更强壮,有利于嫁接苗的快速生长,并促进开花结实,这对童期长且生命周期达上千年的香榧及其他优良种质而言尤其重要。此外,砧苗的分枝数越少,表皮越光滑,嫁接时越方便,越有利于接口的愈合。榧树优良砧木育种资源的选育目前尚未见相关报道。对林木而言,子代测定中包括各方差分量及由其计算的遗传力、遗传相关系数和遗传增益,以及加性效应值等遗传参数的估计来自线性混合模型(linear mixed model, LMM),且林木中的目标改良性状多为数量性状,即连续性状,服从高斯分布,采用普通的线性混合模型即可估算遗传参数。对于诸如存活、干形、颜色、分枝数等非连续性状,早期研究多数采用原始数据或通过转换使数据呈正态和方差齐次后,再采用普通的线性混合模型建模。然而,广义线性混合模型(generalized linear mixed model, GLMM)可以直接对这类表型数据进行分析,无需进行额外处理。尽管常规转换数据的线性混合模型和广义线性混合模型的结果差异不大,但利用广义线性混合模型更合理,且无需担心常规方法数据转换失败等问题[12],此类方法已在动物及林木育种中得到发展,并逐渐普及[13-15]。本研究对天然榧树群体半同胞子代1年生和2年生幼苗生长性状(苗高、地径)和分枝数,分别采用常规线性混合模型和广义线性混合模型拟合并估算相关的遗传参数,以期为天然优良嫁接砧木用榧树种质的选育及利用提供依据。

  • 榧树在自然分布区内资源分布不均,以浙江省最多,安徽黄山市也有较多分布[6]。黄山市徽州区呈坎镇小容村(29°57′N,118°14′E)分布有大量百年以上的野生榧树。2010年10月待榧树种子开始开裂并脱落时,在小容村随机选择50株彼此至少相距50 m以上,生长健壮、正常结实的雌株,每株分别采集不少于50颗种子。种子带回浙江农林大学国家林业与草原局林木良种基地(30°26′N,119°73′E)后,采用双层薄膜结合湿沙储藏催芽法进行种子处理。种子萌发出土后除去稻草及薄膜,按时进行浇水、除草及病害防治等日常管理。2012年3月将培养1 a的幼苗单株移栽至培养钵内。培养钵规格为18 cm×16 cm(直径×高度);培养基质由黄土、泥炭、蛭石和珍珠岩按6∶1∶1∶1(V∶V)混合而成。培养钵按编号摆放于开阔的水平地面上。

  • 移栽结束后,在每个半同胞家系内选择20株生长良好的幼苗进行编号挂牌,然后用电子数显卡尺和卷尺测定苗高(H1,999株)、地径(D1,999株)。由于1年生幼苗多无分枝,所以到具有一定分枝能力的2年生苗时才观察记录分枝数。2013年1月,对挂牌幼苗进行第2次生长性状测定,指标包括苗高(H2,946株)、地径(D2,946株)、分枝数(B2,944株)。

  • 连续性状采用以下常规线性混合模型:

    式(1)中:y为表型观测值向量;β为固定效应向量(均值);u为随机家系效应向量,服从$u \! \sim \! N $$\left( {0,{{I}}\hat \sigma _u^2} \right)$N表示正态分布,I表示单位矩阵,${\rm{\hat \sigma }}_{u}^2$表示家系效应方差;XZ分别表示固定和随机效应的关联矩阵;e表示随机残差向量,服从$e \! \sim \! N\left( {0,{{I}}\hat \sigma _e^2} \right)$${\rm{\hat \sigma }}_{e}^2$表示残差方差。

    非连续性状采用以下广义线性混合模型:

    式(2)~(3)中:η为线性预测值;I(μ)为链接函数;其余项与公式(1)相同。

    统计分析主要由R语言计算平台的ASReml-R包3.0版完成。模型参数由限制性最大似然估计法(REML)估计,随机效应的效应值由最佳无偏线性预测法(BLUP)预测。各方差组分的统计显著性检验由似然比检验(LRT)完成。利用泰勒级数展开法计算遗传参数标准误。

    因为家系数少(50个),每家系取样量也少(20个),采用常规遗传力计算方法得到的遗传力估计值大于1,超出其取值范围(0~1),因此采用CULLIS等[16]提出的方法计算遗传力,公式为:

    式(4)中:Hc为遗传力;V为成对基因型最佳无偏线性预测差值的方差,$\hat \sigma _{\rm{g}}^2 = 4 \hat \sigma _u^2$。遗传力的标准误采用自主抽样法估计。

    采用下式计算拟合双性状模型连续性状xy间的遗传相关(${\hat r_{\rm{g}}}$)和表型相关(${\hat r_{\rm{p}}}$):

    式(5)~(6)中:${\hat \sigma _{{\rm{g}}(xy)}}$${{\rm{\hat \sigma }}_{{\rm{p}}(xy)}}$分别表示性状xy间的加性遗传和表型协方差估计值;${\rm{\hat \sigma }}_{{\rm{g}}(x)}^2$${\rm{\hat \sigma }}_{{\rm{g}}(y)}^2$分别表示性状xy的加性遗传估计值;${\rm{\hat \sigma }}_{{\rm{p}}(x)}^{2{\rm{}}}$${\rm{\hat \sigma }}_{{\rm{p}}(y)}^{2{\rm{}}}$分别表示性状xy的表型方差估计值。由于ASReml-R包3.0版不能拟合含有非连续性状的双变量模型,因而分枝数与生长性状的遗传相关用性状最佳无偏线性预测育种值间的Pearson相关系数替代,表型相关由表型值间的Pearson相关系数替代。

    设定入选率为10%,采用WHITE等[17]提出的公式计算各性状的遗传增益ΔG

    式(7)中:${\bar A_{\rm{s}}}$${\bar A_{\rm{p}}}$分别为入选群体和试验群体的平均育种值。

  • 表1可见:1年生榧树幼苗苗高均值为(19.428±4.465) cm,地径均值为(3.608±0.635) mm;2年生幼苗的平均苗高和地径分别为(29.105±6.267) cm和(4.383±0.630) mm;分枝数为1~17条。苗高和地径在年龄尺度上呈不同程度的变异,总体上苗高的变异系数大于地径,且随年龄的增加而降低;在2 a的观测中,苗高的变异系数均大于20%,地径的变异系数略小(表2)。

    项目 H1/cm H2/cm D1/mm D2/mm B2/条
    均值±标准差 19.428±4.465 29.105±6.267 3.608±0.635 4.383±0.630 7.451±2.902
    最小值 9.00 13.00 1.56 2.64 1
    最大值 35.00 50.00 5.63 6.98 17

    Table 1.  Descriptive statistics for growth and branching traits in T. grandis

  • 表2表明:5个表型性状家系间在统计学上存在极显著差异(P<0.01),说明各性状在家系间存在丰富的变异,具有在家系水平开展选择的潜力。1年生苗高的遗传变异系数最大,第2年分枝数的遗传变异系数最小;遗传变异系数苗高大于地径。苗高和地径表型变异系数与遗传变异系数有相同的变化趋势,且遗传及表型变异系数随年龄的增加而降低,但分枝数的遗传变异系数很小,苗高和地径变异系数则较大。5个表型性状均有较大的遗传力估计值(Hc>0.7),且标准误不大(0.012~0.029)。在相同年龄水平上,苗高的遗传力最高,变幅为0.857~0.943;地径略低,变幅为0.808~0.866;分枝数的遗传力最低,为0.734。在遗传增益上幼苗苗高大于地径及分枝数,1年生枝条的遗传增益最高,达32.60%;苗高和地径的遗传增益第1年高于第2年。

    性状 家系方差 残差方差 遗传力 遗传变异系数/% 表型变异系数/% 遗传增益/%
    H1 9.963(2.134)** 11.932(0.548) 0.943(0.015) 22.98 24.08 32.60
    H2 9.506(2.238)** 29.784(1.407) 0.857(0.014) 14.98 21.54 18.49
    D1 0.099(0.023)** 0.306(0.014) 0.866(0.012) 12.33 17.64 11.65
    D2 0.073(0.018)** 0.326(0.015) 0.808(0.018) 8.72 14.42 8.04
    B2 0.020(0.005)** 1.000(NA) 0.734(0.029) 1.89 13.55 11.00
      说明:括号内数值为标准误;**表示在P<0.01水平上差异显著;NA表示不可用

    Table 2.  Genetic parameters for growth and branching traits in T. grandis

  • 表3可见:同一批榧树幼苗,无论生长年限多长,表型上苗高、地径及分枝数两两间都具有极显著的相关性(P<0.01),且以不同年份地径间及苗高间的相关性较高,说明第1年的生长对第2年的生长有影响;此外,第1年的苗高与第2年的地径,第2年的苗高与第2年的地径及分枝数的相关性处于中等水平,说明苗高的影响比较大。遗传相关表明:不同年份苗高间及地径间相关性高,且相关极显著(P<0.01);而分枝数与第1年的苗高及地径相关不显著,但与当年的苗高及地径相关显著(P<0.05)(表3),说明遗传相关与表型相关格局基本一致,选择第1年苗高及地径数值大的幼苗,第2年苗高及地径值也大。可见,当年的生长影响苗木的分枝。遗传增益的分析结果也是第1年大于第2年(表2)。

    性状H1H2D1D2B2
    H1 1.00 0.61 (0.03) ** 0.53 (0.04) ** 0.51 (0.04) ** 0.20 (0.05) **
    H2 0.84 (0.05) ** 1.00 0.34 (0.04) ** 0.46 (0.03) ** 0.59(0.03) **
    D1 0.63 (0.10) ** 0.51 (0.13) ** 1.00 0.71 (0.02) ** 0.14 (0.04) **
    D2 0.58 (0.11) ** 0.57 (0.12) ** 0.82 (0.06) ** 1.00 0.34(0.04) **
    B2 0.21 (0.16) 0.55(0.13) ** 0.13 (0.18) 0.33(0.16) * 1.00
      说明:上三角是表型相关,下三角是遗传相关;括号内数值为标准误;*表示显著相关(P<0.05),**表示极显著相关(P<0.01)

    Table 3.  Genetic and phenotypic correlations between growth traits

  • 香榧产业发展迅猛,大量榧树用作香榧嫁接的砧木,但用于选育的丰富榧树遗传资源没有得到很好的利用,有必要制订保护策略,对榧树开展遗传基础研究。然而,相对于对香榧生产的重视程度,人们对榧树的兴趣主要在于采种生产砧木苗及采集花粉,仅对包括雌性榧树[1, 18]、雄性榧树及物种水平榧树的遗传多样性开展了研究,未涉及遗传参数的研究。以混合线性模型估算遗传参数和预测相关性状的育种值是一种较为先进的遗传评定方法,已得到了广泛运用[19-20]

    目前,以结果为生产目的的经济树种往往要求树冠开张,这样不仅受光面大,且有利于枝条养分累积、生殖生长和果实的生长发育,可提高经济产量。由于香榧嫁接使用的是2年生砧木,故本研究重点关注幼苗前2年的生长和遗传变异情况。本研究中榧树苗第1年基本没有分枝,第2年绝大多数幼苗产生分枝,且表型变异系数大于遗传变异系数,其遗传力也不低,达0.734±0.029,说明分枝性状受营养条件的影响较大。苗高与地径生长都需要营养。作为砧木,嫁接前要截梢,苗高与地径相比地径更为重要。因此,培育砧木苗可考虑到1年生苗地径比较粗短的雌株上去采种。育种群体的遗传变异(遗传力或加性遗传变异系数)随年龄变化的规律受多个因素影响,如群体组成、群体遗传背景、树种及测试地点的气候及立地条件等。虽然多数研究表明:生长性状的遗传力随年龄的增加先增加而后趋于稳定,但并不总是这样,如杉木Cunninghamia lanceolata[21]、美国黑松Pinus contorta[22]等。此外,榧树生产大粒种子,可食部位主要是胚乳,因而营养含量要远高于其他树种的种子,对幼苗的生长有更为显著的影响。随着幼苗的生长,营养物质逐渐消耗,作用逐渐减弱,可能使家系间差异缩小,加上家系内误差逐渐增大,造成遗传力估计值下降的现象。因此第2年的遗传力小于第1年应该是榧树的正常现象。

    经营管理中的培育措施往往会影响生长性状表现,这在高度集约经营的经济林生产中尤其如此。因此,从优良基因型入手的优良种质选育,结合经营管理中的良法,是促进经济林生产的关键。从分析结果来看,生长性状表型上两两间呈极显著正相关(表3),说明它们的遗传改良可以同步进行[21]。在榧树半同胞幼苗中,苗高与地径性状受较高的遗传力(>0.8)控制,这与黧蒴栲Castanopsis fissa[23]、麻疯树Jatropha curcas[24]等的研究较为一致。此外,各性状的表型变异系数均大于遗传变异系数,且各性状在家系间均存在极显著的差异,表明天然榧树种内存在丰富的变异,具有极高的选育潜力。从年均生长量来看,2 a间地径增量不大,而苗高生长增量较大(表1),且苗高的遗传力也较高(表2),因此可以基于苗高生长尤其是1年生苗的苗高来选择培育砧木的采种树,因为1年生苗高的遗传增益最大(32.60%),基因型的变异系数也最大(16.25%),在相同栽培条件下表型的变异系数最大(24.08%),选择相对容易。榧树生产育苗过程确实发现生长量特别大的优良个体[8]。在育种实践中,由于遗传相关不包括环境因素的影响,因此性状间的遗传相关更为重要。从遗传力相关来看,1年生苗高与2年生苗高及地径均极显著相关。因此,无论从生长性状表型相关还是遗传相关来讲,两者的结果比较一致。

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