南高叢藍莓(Vaccinium hybrid)開花及開花基因表現之環境調控

Abstract

藍莓(Vaccinium sp.)多於夏季長日暖溫環境下行營養生長，於秋季短日涼溫下 花芽分化，後於翌年春季開花。FLOWERING LOCUS T (FT)基因在包含藍莓等多 種植物中，皆被認為具有調控植物生長階段轉變、花芽分化及開花等功能，而 CONSTANS-LIKE (COL)則為光週期感應、FT 上游調控的重要開花路徑基因。少數 南高叢品種，如 ’Blue Muffin’，在溫帶及亞熱帶地區，可終年連續開花，其開花 行為似對日長較不敏感，然而溫度，尤其是高溫，是否具有調控日長對藍莓開花 基因表現之影響力，仍有待釐清。本試驗於 2020 年 4 月至 12 月，將南高叢藍莓 品種‘Blue Muffin’(BM)、‘Sunshine Blue’(SB)及‘Georgia Gem’(GG)，栽培於日夜溫 35/30°C、25/20°C 或 20/15°C，自然光照條件之人工氣候室。每週紀錄花芽分化數 量與營養生長;每三週進行葉片採樣，檢測 VcFT 及 VcCOL5 之基因表現量，以 釐清溫度與日長對藍莓生長調控之交互作用。 實驗結果顯示，在高溫下(35/30°C)，SB 與 GG 的營養生長受到促進，營養芽 萌發期延長至 10 月(日長<12 小時)，營養生長高峰期 6~8 月間之停心率低於其他 兩處理(多低於 60%)，且試驗期間皆無花芽形成。BM 營養芽萌芽時間亦延長，然 而停心率和其他溫度處理相近，6 至 8 月間之停心率維持在 60~80%，試驗期間植 株持續形成花芽並開花，但其花芽型態明顯和其他溫度處理者有明顯差異，單一 花芽之花朵數明顯少於另二溫度處理者，且花芽形成集中於枝條頂芽，其形成花 芽之枝條比例及腋芽轉為花芽之比例也低於其他二溫度處理。在整個試驗期間， 三品種之 VcFT 均受到抑制，雖然在 10 月日長減短後略有上升，但仍遠低於其他 二處理組。 在適溫(25/20°C) 下，SB 和 GG 之營養生長指標在三處理組中居次，營養芽 在九月底後即停止萌發(日長<12 小時)，6 至 8 月間停心率>60%，並於 10 月初， 日長小於 12 小時之環境，可見腋芽轉化為花芽。SB 和 GG 在此溫度下，5 到 9 月 VcFT 基因表現量低，和高溫處理組同時間之表現量相似，在 10 月後(日長<12 小時)表現量開始明顯上升，達表現高峰。BM 之營養生長指標和涼溫處理組相似，7、 8 月停心率約在 80%，9 月後幾無營養芽萌發，萌芽期短於高溫處理者，並於 5 月 開始即有花芽形成並開花，花芽形成位置多在腋芽，每一花芽皆分化出 4 至 10 個 花朵。BM 於此處理下，VcFT 基因於整個試驗期間仍維持低表現量，和高溫處理 之 BM 表現模式相近，沒有明顯高峰。 在涼溫(20/15°C)環境下， SB 和 GG 之營養芽萌發停止早於其他二處理者， 於 8 月底即不再萌芽(日長>12 小時)，且停心率上升最快，於 6 至 8 月近 80%枝 條停心，於在 7 月底、8 月初(日長接近 13 小時)即可見花芽形成，在此涼溫下， SB 形成花芽枝條數量及 GG 腋芽分化花芽之比例皆上升，而 VcFT 表現量於 8 月 底、9 月初(日長>12 小時)即開始顯著上升。BM 之營養生長在萌芽時間、停心率 上皆相似於適溫處理組，但於 4 月即有花芽形成，花芽數量、型態上和適溫處理 相近，但腋芽轉變為花芽比例更高，而 VcFT 基因仍全程維持低表現量。 VcCOL 5 基因在各處理各品種間有相似的表現模式，皆隨不同日長而改變表 現量，在 5 至 8 月日長增加表現量逐步減少，9 月後日長減短表現量逐漸上升，溫 度對其影響不若對 VcFT 基因之影響顯著，僅高溫處理略低於其他處理者。 試驗結果說明，即便於短日環境，高溫可促進一般藍莓品種的營養生長，並 抑制短日對腋芽分化為花芽的作用，而低溫則可於長日下抑制營養生長，並促進 花芽形成。一般藍莓品種 SB 和 GG 之 VcFT 的表現和其對光週期的敏感性均受溫 度調節，且 VcFT 和藍莓花芽形成具有高度相關性，低溫環境其提早表現導致早花。 而 VcCOL 5 在不同溫度處理下，差異並不顯著，表現主要受到日長調控。相較之 下，BM 品種之 VcFT 基因在三個處理皆為三品種中最低，VcCOL 5 表現模式則近 於其他品種，其連續開花之成因應肇因於其他調控途徑。

Flower buds of blueberry are generally induced by cool temperature with short-day conditions in autumn. Previous studies have shown that FLOWERING LOCUS T (FT) was involved in the transition of vegetative growth to reproductive growth while CONSTANS-LIKE (COL) genes responsive to photoperiod regulate expression of FT in many plant species. Some new blueberry cultivars such as ‘Blue Muffin’ show a perpetual blooming behavior and varied flowering seasons between plants cultivated in temperate and subtropical climates, indicating that their flowering genes might by less sensitive to photoperiod. To document the effects of two essential environmental factors, i.e., temperature, especially high temperature, and photoperiod on flower bud differentiation and expression of flowering genes, ‘Blue Muffin’ (BM), ‘Sunshine Blue’ (SB), and ‘Georgia Gem’ (GG) southern highbush blueberries were cultivated in phytotrons with day/night temperatures of 35/30°C, 25/20°C, or 20/15°C and natural photoperiods. Vegetative growth and flowering status were recorded weekly. Leaves were sampled and the expression of the flowering related genes FLOWERING LOCUS T (VcFT) and CONSTANS-LIKE 5-like (VcCOL5) were analyzed weekly and once every three weeks from April to December 2020. At high temperature (35/30°C), Tthe vegetative growth was extended in three cultivars. Vegetative budbreak continued in October (day length<12 hr). Flower bud formation was observed only in BM through the experimental period regardless of the day length. However, the number of flower bud was lower and the development was poorer than those in the other two temperature treatments. The expression level of VcFT was suppressed in all three cultivars through the experiment period. At mild temperature (25/20°C), the vegetative growth of SB and GG ceased earlier than that under high temperature treatment. Flower buds were observed in these twocultivars in early October when day length < 12 hours. The expression level of VcFT was low in SB and GG from May to September but was promoted after October. In this treatment, little vegetative bud break in BM after September. Flower buds of BM continuously differentiated from May to November. Flower buds were well developed from axillary buds with 4 to 6 flowers per bud. VcFT gene expression level remained low through all the period in BM. At cool temperature (20/15°C), the vegetative growth of all cultivars was retarded. Vegetative budbreak rate was low and ceased early in late August when daylength was still >12 hr). Flower buds in SB and GG were observed from July and August when daylength close to 13 hours. The expression level of VcFT were promoted from August and September. On the other hand, flower buds of BM were observed from April and the expression of VcFT gene remained low . The expression level of VcCOL 5 showed no difference under different temperatures between all cultivars but was regulated by day length. The results suggested that high temperature (35/30°C) treatment encourages vegetative growth of the three cultivars in short daylength (<12 hr) while suppressed flower bud formation in SB and GG but not in BM. On the contrary, cool temperature (20/15°C) treatment advanced flower bud formation in long daylength (> 13 hr). The expression of VcFT and VcFT sensitivity to photoperiod were both regulated by temperatures in SB and GG. The early flowering in cool temperature results from the early expression peak of VcFT. The lowest VcFT and VcCOL 5 expression level in BM subjected to 35/30°C might indicate that blooming of BM in high temperature and long day conditions might be enforced by other flowering pathways and genes.