反季節兔眼藍莓之開花與授粉

Abstract

在亞熱帶氣候下種植的兔眼藍莓(Vaccinium virgatum Aiton)，秋季經常在頂 梢出現反季節開花的現象，具有產期調節的生產潛力。本論文研究目的在透過對開 花和授粉的研究，探討對果實產量與品質的影響，來提高反季節藍莓果實的生產力。 根據在亞熱帶氣候中的觀察，本論文的假說為，溫暖的秋季溫度有利於營養生長持 續生長，但同時期的短日長則誘導頂梢生長點花芽分化，進而導致某些兔眼藍莓品 種的反季節開花現象。為了證明這一假說，本論文分析兔眼藍莓’NTU031’和’Austin’ 的開花行為和開花相關基因(VcFT，VcCEN 和 VcCOL5)的表現。從 11 月下旬開 始，’NTU031’枝梢未停心且直接開花，而’Austin’大多數頂芽都已停心。在’NTU031’ 中，VcFT(開花啟動子)的表達在 10 月中旬增加，而 VcCEN(開花抑制子)和 VcCOL5(光週期誘導開花的抑制子)的表達則明顯下降。然而同時期在’Austin’上， 上述基因的表達沒有明顯的波動。結果顯示，VcFT 轉錄的變化與’NTU031’的反季 節開花呈正相關，而 VcCEN 和 VcCOL5 表達的變化與反季節開花呈負相關。 反季節花朵所產生的果實通常較小，這可能是由於缺乏花粉和昆蟲授粉媒介 來進行異花授粉所致。本論文對四個反季節開花品種和品系進行了人工授粉試驗， 以驗證此假說。在所有品種中，異花授粉增加漿果的直徑、重量、種子數量且縮短 漿果發育日數。種子數量與漿果重量之間呈正相關，種子數量與漿果發育時期之間 則呈負相關，顯示種子刺激了果實的發育。根據授粉試驗，與其他品種相 比，’NTU025’ 開放授粉可得更大的果實。為測試’NTU025’中自交和單性結實的可 能性，分別進行了花粉管生長觀察和無花粉處理。結果發現，’NTU025’在無授粉 條件下亦可結實，顯示’NTU025’具有單性結實能力。自花授粉後，其花粉管生長 可到達胚珠。然而，果實中並未產生種子，顯示自花受粉後，可能未完成受精，或 自花受精後的胚珠並未發育。儘管人工授粉可以有效地改善反季節水果的質量，但 耗時且勞力需求大，因此，’NTU025’等自花結實品種對反季節水果的生產非常有價值。總結授粉試驗的結果，增加異花授粉的機會或利用像’NTU025’這樣的自花 結實的品種將提高反季節生產力。這些研究將成為臺灣反季節兔眼藍莓生產的基 礎。

Rabbiteye blueberries (Vaccinium virgatum Aiton) cultivated in the subtropical climate often display off-season flowering on the shoot apices, which offers a potential for off-season berry production. The aim of this study was to elevate off-season productivity through the research on flowering and pollination, which directly determine yield. According to filed observations in the subtropical climate, it was hypothesized that the mild autumn temperature favors vegetative growth while the concurrent short photoperiod promotes flower differentiation in the shoot apex, resulting in off-season blooming in some rabbiteye blueberry cultivars. To prove this hypothesis, the flowering behavior and expression of flowering-related genes (VcFT, VcCEN, and VcCOL5) in rabbiteye blueberry ‘NTU031’ and ‘Austin’ were analyzed. ‘NTU031’ showed off- season flowering on growing shoots from late Nov. while most shoots of ‘Austin’ terminated. In ‘NTU031’, VcFT (flowering promoter) expression increased in mid Oct. whereas VcCEN (flowering repressor) and VcCOL5 (photoperiod-mediated flowering) expression decreased. On the other hand, ‘Austin’ did not show any significant fluctuation in the expression of the mentioned genes. The results suggested that changes in the transcription of VcFT positively correlated with off-season flowering and changes in VcCEN and VcCOL5 expression negatively correlated with off-season flowering. Berries produced from the off-season flowers are usually small probably due to the shortage of pollen donors and insect pollinators for cross-pollination. Artificial pollination trials to four off-season flowering cultivars and breeding lines were carried out to test this hypothesis. In all cultivars, cross-pollination increased berry diameter, weight, seed number, and advanced berry ripening. A positive correlation between seednumber and berry weight and a negative correlation between seed number and berry developing period were observed, suggesting that seeds stimulate fruit development. In open-pollination tests, ‘NTU025’ produced bigger berries than other cultivars. To test the possibility of self-compatibility and parthenocarpy in ‘NTU025’, pollen tube growth observation and no-pollination treatment were conducted. Interestingly, ‘NTU025’ set normal sized fruit without pollination, indicating that ‘NTU025’ is parthenocarpic. In addition, pollen tube reached ovules in self-pollinated ‘NTU025’ but no seed was formed, suggesting that fertilization failed or fertilized ovules failed to develop into seeds. Although artificial pollination was effective to improve off-season fruit quality, it is time-consuming and labor-intensive. Therefore, self-fruitful cultivars such as ‘NTU025’ are valuable for off-season fruit production. In conclusion of the pollination test, to increase chances of cross-pollination or utilize self-fruitful cultivars like ‘NTU025’ will elevate the off-season productivity. These studies will provide insights into the development of off-season rabbiteye blueberry production in Taiwan.