紅光及黑暗處理對培養短節間矮生型桃微體繁殖芽之影響

Effect of Red Light and Dark Treatment on Culturing Micropropagated Shootsof Brachytic Dwarf Peach [Prunuspersica (L.) Batsch]

桃樹[Prunus persica（L.）Batsch]具短節間矮生性狀者又稱矮性桃（brachytic dwarf peach tree），在果園經營管理作為砧木使用時，有降低接穗生長活力形成較矮樹冠，便於田間操作等優勢。惟若實際推廣採用本方法時，砧木的需求要靠大量無性繁殖來支持。本研究利用微體繁殖法建立兩種矮性桃brachytic dwarfism 1（BD1）與2（BD2）的繁殖系統。先將新梢的帶節莖段培養於添加4.44µΜ6-benzyladeninepourine（BAP）及0.49μΜindole-3-butyric acid（IBA）的Woody Plant Medium（WPM）培養基中進行側芽誘導，可建立無菌培養之芽體。再於芽體增殖及抽長階段將芽培殖體在添加2.22μΜBAP及0.049μΜIBA的WPM培養基中，分別進行黑暗及紅光處理，發根階段則將源自兩種不同光環境處理之芽體個別以IBA進行二階段發根誘導馴化。試驗結果顯示BD1及BD2之芽體皆以紅光處理後可獲得較佳的芽體增殖與大芽（≥1.5 cm）數量。惟BD1及BD2芽體發根條件並不一致，BD1芽體不論接受何種光環境處理，皆以14.8µM IBA刺激96 h可獲得最佳發根率（> 90%）及馴化率（> 71%），使其繁殖效果最佳。而來自兩種光環境處理過的BD2芽體，則以49.2µM IBA刺激48 h可獲致較佳之繁殖效果，發根率為80%~85%，但馴化率偏低。BD2芽體在發根階段有頂芽壞疽（shoot tip necrosis）及葉片黃化掉落的現象，以致小植株馴化時存活率不佳，需將其發根階段培養時間縮短以降低這些負面影響。總體而言，使用紅光培養相較於黑暗處理可有效促進BD1與BD2芽體之增殖並育成較多之大芽，而後續發根與馴化之條件則須依材料不同，處理各異。本研究建立之培養條件除可有效繁殖矮性桃作為根砧之外，亦可供參考用於其他矮性樹種的微體繁殖操作。

Peach trees [Prunus persica(L.) Batsch] with short internodes and brachytic dwarf phenotype are preferably employed in orchard management as superior rootstocks. They diminished scion which provides the benefit of restraining tree-crown size, greatly facilitating orchard operations. However, to implement this method effectively, a sufficient number of true-to-type asexual propagules is required to meet the demand for rootstocks. The present study established a micropropagation protocol for two types of dwarf peaches, namely brachytic dwarfism 1 (BD1) and brachytic dwarfism 2 (BD2). Nodal segments of newly-grow sprouts wereincubated on Woody Plant Medium (WPM) supplemented with 4.44μΜ6-benzyladenine (BAP) and 0.49μΜindole-3-butyric acid (IBA) to obtain sterile shoot cultures. At the proliferation and elongation stages, the shoot explants were incubated in the same WPM medium supplemented with 2.22μΜBAP and 0.049μΜIBA. In addition, to stimulate shootelongation, the explants were either exposed to darkness or red light. In root induction stage followed by plantlet acclimatization stage, elongated shoots from two distinct light environments were subjected to IBA stimulation. The results indicated that both BD1 and BD2 shoots, when treated with red light, exhibited enhanced shoot proliferation and increased amount of large shoots (≥1.5 cm in length). However, the optimal rooting condition differed for BD1 and BD2. For BD1 shoots, whether obtained from dark or red light conditions, 14.8µM IBA stimulation for 96 h resulted in satisfactory propagation efficiency with best rooting percentage (>90%) and acclimatization survival (>71%). However, BD2 shoots under same light treatment exhibited less in vitropropagation efficiency with a rooting percentage of 80%~85% but low survival rate from 49.2µM IBA stimulation for 48 h. The low plantlet survival rate in BD2 shoots was attributed to shoot tip necrosis, and both leaf yellowing and falling that occurred during rooting. Shortening the rooting period could mitigate these constrains. In conclusion, red light incubation significantly enhanced shoot proliferation and promoted large shoot formation in both BD1 and BD2 shoots. However, the subsequent rooting and acclimatization processes were genotype-dependent. The protocol developed in this study not only facilitates the propagation of dwarf peaches used as rootstocks but also serves as a possible technique for the micropropagation of other dwarf tree species.