伽瑪射線誘變對“愛文”芒果矮化之效應

Effect of Gamma Ray on Induction of Dwarfism-like “Irwin” Mango (Mangifera indica L.) After Treatment

矮化芒果栽培可提高土地利用率，相對降低生產成本。誘變在果樹育種上可免去幼年性長的限制，並導入重要園藝性狀，如樹勢減小、果色改變及緊密生長型等。本試驗以放射線處理愛文芒果種子後，將之播種並定植田間，探究植株高度於放射線照射後的反應，以期有機會選育矮型株。愛文芒果種子以2-krad伽瑪射線第一次照射後，存活率為65.2%。於二次抽梢後，再從被照射族群中選約120株表現如同未照射者做第二次照射，放射線照射後於溫室內培育半年。比較未照射之對照組、照射一次者以及照射二次者的植株高度，對照組平均植株高度42.4cm,非常顯著較處理組高。定植田間四個月後，對照組平均植株高度78.7cm,照射一次者植株高度55.1cm,照射二次者與對照組沒有顯著差異。依植株高度50及90cm將各處理分為高、中、矮不同生長勢，其中照射一次矮型株佔45.6%,照射二次之矮型株佔13.8%:半年後再調查處理組矮型株平均株高約64cm,而高型株約為140cm,中型株則約95cm。卡方測試（X2=28.12, P<0.01）顯示，伽瑪放射照射明顯影響植株高度。矮型株之植株高度頻度分佈與高型者有顯著差別。伽瑪射線照射後15個月矮化的愛文芒果植株仍保持矮化。然植株高度的改變是否源自遺傳質的變異仍需進行研究。

Reduction of mango size would provide an opportunity to increase land utilization efficiency and to decrease production cost. The use of mutagenesis for fruit tree breeding could overcome some limitations, such as long juvenile period of seedling; and introduce important horticultural traits such as plant size reduction, fruit color, and compact growth habit. The responses of mango, treated with gamma ray, were investigated on'Irwin'in the greenhouse and in the filed condition. The survival ratio of'Irwin'seedlings was 65.2% after 2-krad gamma ray radiation. The same dosage was applied again on visually normal-looking 'Irwin' seedlings, which were surveyed after the secondary shoot growth in the greenhouse. Comparisons were made on I) the control, without radiation treatment, 2) radiation once, and 3) radiation twice. The mean plant height of the half-year-old control seedlings in the greenhouse was 42.4cm, which was significantly higher than the radiated seedlings. The mean plant height of the control mango seedlings was 78. 7 cm four months after planting in the field. The radiation once group had a mean plant height of 55.1 cm. The radiation twice group was as high as the control. Plant heights less than 50 cm would considered as dwarf ones which occupied 45.6% of the treatment one in July of 1998. The proportion was 13.8% of the plant height less than 50 cm for the radiation twice group. The height of dwarf'Irwin' plants were about 64 cm surveyed in January of 1999. However, the mean plant height of the high group was about 140 cm and the intermediate group was about 95 cm. The radiation would dramatically affect plant height according to the independence test of Chi-square (x 2 =28.12, p<0.01). The frequency d 1stribut10n after radiation treatment could be divided into three groups. The dwarfism distribution was distinct to the distribution of high group of the plant height. The radiation was effective reduction of the plant height of'Irwin'mango. Further studies are needed to investigate changes of plant height due to the genetic effect.