腰果的生產與遺傳改進

Production and Genetic Improvement of Cashew

印度是世界腰果（＂Anacardium occidentale＂L., cashew）種仁（kernel）外銷第一大國，自1950年代即開始進行研究發展，產業初起是從種原實生選育高產單株為新品種，但忽略種仁的質與量，繼而加強種仁大小等級超過W320（W320為腰果種仁重量分級在1.42-1.88g之間，每英鎊含種仁數320粒）與較高出仁率（shelling percentage）等特性的選拔，創造質、量兼顧的新品種。在澳大利亞鄉村產業研究與發展部（Rural Industries Research and Development Corporation），其推動腰果品種改良的策略是利用樹冠生產力並導入種仁市場價值，再以實生苗的經濟價值高低當作選拔的參考依據，並將此一概念量化為評估育種值（estimates breeding values, EVB），以此數據決定第二世代（next generation）雜交親本性狀的選拔，不但提升育種效率且達成育種目標。本論述並導入影響波斯核桃（＂Juglans regia＂L., Persianwalnut）與長山核桃﹝＂Carya illinoinensis＂（Wangenh.）K. Koch, pecan﹞產量高低與樹形結構的關聯性，來提升腰果育種效率。亦即腰果實生後代於開花時期有較多的側枝發生數目與較高比率的側枝結實性為選拔指標，以此育種策略改進腰果產量因素的合理遺傳獲得量。臺灣開發理想的腰果新品種，應具備耐寒性強、高產、高出仁率、高單價種仁等級、營養價值高、抗生物與非生物逆境等特性的新品種，以加速產業發展。此外，持續從國外各研究所收集、評估與利用腰果種原；加強矮生與緊密型的種原研究，創新腰果高密度種植栽培系統，提升單位面積產值；建立優良品種或單株的種苗繁殖技術，大量供應名符其實的優良種苗木等；將是未來研究的重點。 India is the leading producing country in the world to export the kernel of cashew (＂Anacardium occidentale＂ L.) for international trade. Cashew research in India started way back in the 1950s. The initiation of the India nut industry was to select cultivars by yield realized per tree from germplasm materials. This has resulted in the release of cultivars with kernel grades of less than W320 (kernel grades 1.42-1.88 g, 320 kernels per pound), so that the characteristics of kernel weight, grade, and shelling percentage received much more attention for crop improvement. The Rural Industries Research and Development Corporation of Australia has developed a breeding strategy for selection of new cashew hybrids by evaluating canopy productivity and its derivative trait value. Hybrids were selected as potential new parents based on estimated breeding values (EVB) to improve the value trait in the next generation. The author showed that the most important reason for low yield in pecan [＂Carya illinoinensis＂ (Wangenh.) K. Koch] as compared with high yield in Persian walnuts (＂Juglans regia＂ L.) is the comparatively fewer lateral shoots. Rapid genetic gain for yield potential could be achieved in cashew breeding by selecting for much more lateral shoots and higher percentage of shoots fruitfulness during flowering period. The cashew cultivar improvement in Taiwan should focus mainly on chilling tolerance, high nut yield, high shelling percentage, high value of kernel grade, fixing nutrient requirement, and resistance to biotic and abiotic stresses. Meanwhile, our aims in the future will be to collect germplasm materials from foreign cashew research centers, to concentrate on dwarfing and compact plant types for high density planting, and to standardize vegetative propagation techniques for producing quality seedlings.