相思樹在台灣種源後裔試驗之6年生長與樹幹性狀之遺傳變異

相思樹為台灣林木改良重要的計畫，主要原因是相思樹是菇蕈業太空包培養香菇的重要木屑來源，支撐約百億元台幣的菇蕈業產值。台灣政府在2014年起獎勵相思樹在休耕地造林。為了評估相思樹的遺傳增益及快速提供改良種子，在2011年時，我們從台灣六地區具有千株優良林分各10株優勢木（選擇強度1%），利用嫁接種子苗建立營養系苗。本研究將台灣中西部的嘉義、東北部的宜蘭、及東南部的台東共3種源17家系自然授粉種子培育成苗，在2012年12月於台灣中東部花蓮光復建立逢機不完全區集的種源後裔試驗，試區共10區集，其中8區集有17家系，2區集有15家系，每小區栽植10株，栽植距離2 × 2 m。試區調查3至6年生的生長性狀，包括：樹高、胸徑、每公頃材積，形質性狀包括：樹幹通直度、分叉位置、分叉角度、及側枝數，分析這些性狀的遺傳參數與年齡間相關性。本研究顯示所有性狀在種源間與種源內家系間差異顯著，僅有樹幹通直度在家系間差異不顯著。6年生材積生長為例，宜蘭、台東與嘉義種源各為80.6、32.1、25.3 m^3 ha^(-1)，而家系間差異則宜蘭最佳家系Y-1對最差的嘉義家系C-4之6為105.8與20.0 m^3 ha^(-1)，顯示種源家系的選育非常重要。材積生長的3年生年齡與6年生間的相關分析係數0.83，為極顯著正相關，顯示早期選育是可行的。3至6年生的樹高、胸徑與材積的單株遺傳力（h^2i）數值變化不大，各為0.27～0.22、0.43～0.43、0.30～0.32。而家系遺傳力（h^2f）則呈現上升趨勢：3性狀各為0.04～0.08，0.11～0.32，與0.10～0.39。遺傳增益（ΔG（%））在胸徑及材積生長在各年齡各為25.2～23.9與46.9～50.6，數值變化不大，但樹高則呈現下滑從11.7降至5.3。樹幹性狀中通直度、分叉位置與分叉角度的單株與家系遺傳力都低於0.1，但側枝數的遺傳力較高各為0.34與0.30。林木樹幹性狀的低遺傳力，可能與颱風侵襲傷害林木有關，2013至2017年每年直接侵襲的中、強度颱風都有1至2個。在相關分析中，側枝數與生長性狀無顯著相關，側枝數的多寡並沒有影響林木生長。不過通直度與分叉角度與6年生樹高、胸徑與材積均呈顯著負相關，由於通直度與分叉位置數值越高，樹幹扭曲度越大而分叉位置越低，因此可選育出生長快速兼具良好樹幹形質。分叉角度與林木生長性狀呈極顯著相關，顯示冠幅開展的林木生長較佳。

關鍵字

相思樹；種源後裔試驗；遺傳力；遺傳增益；選育

並列摘要

Tree improvement of Acacia confusa has been an important project in Taiwan. Its sawdust is a major source of culture bags for culturing mushrooms. To support the requirement of the mushroom industry valued at about New Taiwan (NT)$10 billion (≈US$333 million), the Taiwanese government promoted a policy of subsidizing reforestation of this tree species on fallow land in 2014. To estimate genetic gains and rapidly supply improved seeds, we selected 60 plus trees from 7 better stands called provenances located in northern, central, southern, northeastern, southeastern, and southern parts of Taiwan, with a selection intensity of 1% plus trees selected in each stand in 2011. All of them were cloned by grafting onto seedlings, and a seed orchard was established at Liukuei, Kaohsiung City in 2012. Seedlings raised from openly pollinated seeds collected from 17 families within 3 stands called provenances from Chiayi in west-central Taiwan, Yilan in northeastern Taiwan, and Taitung in southeastern Taiwan were planted in Guangfu, Hualien County, eastcentral Taiwan in December 2012, using a randomized incomplete block design in 10 blocks with 10 trees per plot, with 8 of each block including 17 families, and the other 2 blocks including 15 families. The planting density was 2 × 2 m. Genetic parameters, performances of the provenances and families, and age-age correlations with tree growth characteristics, such as height, diameter at breast height (DBH), volume per hectare, and survival rate, and stem traits, such as the degree of stem straightness, forking position, forking angle, and branching number were investigated at the ages of 3~6 yr. This study revealed significant variance among provenances and families within provenances for all traits [not straits/strains], except for no significance of stem straightness among families. For example, growth volumes of 6-yr-old trees in the Yilan, Taitung, and Chiayi provenances were 80.6, 32.1, and 25.3 m^3 ha^(-1), respectively, while the best family of Yilan-1 vs. the worst family Chaiyi-4 was 105.8 vs. 20.0 m^3 ha^(-1), showing both provenance and family selection are very important for A. confusa breeding. Age-age correlations of volume (a 0.83 correlation coefficient for 3~6-yr-old trees) were very significant strong and positive, indicating that early selection could be made. Individual heritability (h^2i) of height, DBH, and volume for 3~6-yr-old trees appeared to be minor changes which ranged 0.27~0.22, 0.43~0.43, 0.30~0.32, respectively, while family heritability (h^2f) showed a growing trend which ranged 0.04~0.08, 0.11~0.32, and 0.10~0.39, respectively. Genetic gains (ΔG (%)) indicated few changes in DBH and volume ranging 25.2~23.9 and 46.9~50.6, respectively, but height dropped from 11.7 to 5.3. The h^2i and h^2f values of stem straightness, forking position, and forking angle were ＜ 0.1, but branching number showed higher heritability at 0.34 and 0.30, respectively. The lower heritability of stem traits might be related to some injury by typhoon damage. In 2013 to 2017, 1 or 2 moderate or strong typhoons every year directly affected the plantation. In the correlation analysis, the branching number did not affect tree growth as there was no significant correlation between them; however, stem straightness and forking were negatively correlated with 6-yr-old height, DBH, and volume. Greater values of stem straightness and forking position indicating less stem distortion and a lower forking position means that we can select rapidly growing trees coupled with good stem traits. However, growth traits were positively and significantly correlated with forking angle, indicating that trees with a wider crown had better growth.

並列關鍵字

Acacia confusa ； provenance and progeny test ； heritability ； genetic gain ； selection and breeding

國際替代計量

相思樹在台灣種源後裔試驗之6年生長與樹幹性狀之遺傳變異

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