紅龍果物候期、耐寒指標之建立與溫度對開花及結實之影響

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論文名稱: 紅龍果物候期、耐寒指標之建立與溫度對開花及結實之影響
研究生姓名: 朱堉君
指導教授姓名: 張哲嘉
出版年: 2021
學校名稱: 國立中興大學
系所名稱: 園藝學系所
關鍵字: 耐寒指標;開花;結實;生育階段;高溫逆境;低溫逆境;chilling tolerance indicator;flowering;fruiting;growth stage;high temperature stress;low temperature stress
摘要: 紅龍果(Hylocereus spp.)為深具發展潛力的新興果樹。然目前紅肉品種(H. polyrhizus)各生育階段之描述與界定仍有混淆,溫度因子常造成生產之限制,且尚未有耐溫度逆境品種育成。為因應科研及產業對紅肉品種紅龍果各生育階段的界定的需求,本研究進行紅肉種紅龍果生育期編碼─BBCH (Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie)量表制定;釐清長日誘導光週下,溫度對紅龍果開花的調控;探討高溫下,紅龍果開花、結實的過程及導致小果化之機制;並確認是否可利用葉綠素螢光建立耐寒品系之篩選指標。 依據BBCH量表原則,以三位數編碼制訂的紅肉種紅龍果BBCH量表分為主要生長期及次要生長期,主要生長期為第0期─芽體萌發;第1期─刺座發育;第3期─枝條發育;第5期─花芽萌發及花器發育;第6期─開花;第7期─果實發育;第8期─果實成熟;次要生長期則包含37個時期。紅肉種的果肉在果實發育初期發育(code 711),並在發育後期開始轉色(code 719);果皮的轉色則是在果實成熟初期表現(code 811);在果實最後發育階段(code 819),果皮、果肉及內果皮均完成轉色,表示果實已完全成熟。 以白肉種紅龍果(H. undatus)盆栽分別於2016年及2017年3月下旬進行兩階段試驗,探討長日光週下,溫度對紅龍果芽體發育及萌發之影響。2016年試驗的溫度處理為32/22°C(對照組)及23/13°C(低溫),當對照組開始萌花後,每4週將低溫處理組升溫2°C,直到低溫處理組花芽萌出為止。2017年之試驗處理為32/22°C(適溫)、29/19°C(開花需求溫度)及25/15°C(低溫),當29/19°C處理組萌花後2週,將低溫處理組升溫至27/17°C。2016年結果顯示,長日光週下,對照組(32/22°C)的暖溫會促進芽體發育,且在處理3-4週後即能誘導花芽萌發,以每1-2週的頻率萌花1批,表示32/22°C為芽體發育及生殖芽萌發的適溫。相較暖溫,低溫處理(23/13°C)會抑制生殖芽的發育及萌發,直到升溫至29/19°C,生殖芽才能萌發。2017年的試驗植株在29/19°C處理9週後,第1個生殖芽萌發,顯示29/19°C應為白肉種紅龍果生殖芽萌發的最低需求溫度。營養芽的萌發則不受本研究低溫處理(23/13°C)的限制。 以對高溫敏感的紅肉品種‘大紅’(H. polyrhizus),分別於2015年及2017年探討高溫(40/30℃)、適溫(30/20℃)及輕微高溫(35/25℃,2017)下紅龍果開花、結實及枝條生育情形,以釐清高溫期小果化之原因。‘大紅’紅龍果花芽發育到開花日數會隨溫度增加而減少;高溫會縮短花朵長度,輕微高溫則不影響花朵性狀。適溫、輕微高溫及高溫的花粉活力分別為65.1%、8.9%及0.6%,表示高溫嚴重抑制雄花器功能。使用三種溫度處理下的花粉及雌蕊進行互交,高溫下花朵自交的著果率為16.7-29.2%,單果重僅72.1-110 g,果實發育遲緩,種子重皆小於1 g,然授予活力較高的輕微高溫或適溫下發育之花粉,著果率可恢復為100%,單果重及種子重皆會增加,表示雌花器在高溫下維持較高的功能性。輕微高溫下的雌蕊經由人工授粉自交或授予適溫下發育的花粉,果實皆正常發育,故輕微高溫不影響雌花器之功能。近軸端枝條於溫度處理前受高光影響,呈現較遠軸端較高的黃化程度,Fv/Fm較低;處理後1週3種處理皆表現復綠,僅高溫維持較高的黃化狀態;植株的Fv/Fm反應於處理2週後表現,適溫及輕微高溫處理近軸端Fv/Fm皆回升至健康植株的常數0.83,而高溫處理的近軸端及遠軸端Fv/Fm皆持續降低至試驗結束,表示高溫期間的光合作用效能會降低。 於2016年1月寒流後,於田間篩選並取得5個耐寒紅龍果品系,與4個不耐寒之品種(系)之扦插苗,以6℃(低溫)及25℃(對照)處理6天,於調查處理前、回溫後0、4、8、24、72小時調查枝條黃化及葉綠素反應,評估品系之耐寒性並建立篩選指標。結果顯示,各品種(系)在低溫處理前後,其枝條a*值及b*值均無顯著變化;而Fv/Fm於低溫處理後均顯著降低,但耐寒品系可維持較高值,且在4小時後即回復正常值,非耐寒品系則在72小時後回復,顯示葉綠素螢光可作為紅龍果耐寒性之篩選指標。 本研究完成紅肉種各生育階段BBCH量表的制定,並區別出與白肉種相異之部分,可供研究及田間操作參考;證實長日光週下,芽體之發育及生殖芽萌發皆受到溫度調控,生殖芽在滿足最低溫度需求才得以萌發;確認高溫為降低花粉活力,使受精不良、種子重減少導致夏季小果化之主因;而利用葉綠素螢光可做為篩選耐寒植株指標,將可加速耐逆境品種之育成。Pitaya or dragon fruit (Hylocereus spp.) is a novel fruit crop with high economical potential over recent decades. The purpose of this study is aimed to establish phenological growth stages according to the BBCH (Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie) scale and chilling tolerance indicator by chlorophyll fluorescence and assessed the effects of temperature on flowering and fruiting on pitaya. The phenological description of the phenological stages was recorded using a three-digit numerical system, according to the BBCH scale rule on red-fleshed pitaya ‘Da Hong’ (H. polyrhizus). Furthermore, we simultaneously assessed and recorded the flesh color at each stage to address fruit developmental characteristics because of its red flesh. Pitaya contains betalain, a water-soluble pigment that confers red or purple coloration to its flesh and peel. The flesh started to grow in the first stage of fruit development (code 711). The color changed at the final phase of fruit development for the flesh (code 719) and at the first phase of fruit maturity for the peel (code 811). The peel color in the flesh and mesocarp changed entirely in the final stage (code 819), indicating complete fruit maturity. We performed two phytotron experiments to clarify these effects in 2–3-year-old field-grown, potted white-fleshed pitaya (Hylocereus undatus ‘VN White’) under an inductive long-day photoperiod (14/10 h). Experiment I was conducted in late March 2016 and used day/night temperatures of 32°C/22°C (control) and 23°C/13°C (low temperatures), while experiment II was conducted in late March 2017 and used temperatures of 32°C/22°C (optimal temperature), 29°C/19°C (required temperature), and 25°C/15°C (low temperature). In experiment I, the temperature of the low-temperature treatment was increased by 2°C every four weeks from the emergence of reproductive buds in the 32°C/22°C treatment until reproductive bud formation. In contrast, in experiment II, the temperature of the low temperature treatment was increased to 27°C/17°C two weeks after the first reproductive buds emerged in the 29°C/19°C treatment. Experiment I showed that temperature did not affect vegetative bud emergence. However, warm temperatures (32°C/22°C) enhanced bud development and induced reproductive bud emergence 3–4 weeks after treatment, whereas most buds remained in a pre-reproductive stage under the low-temperature treatment (23°C/13°C). Low-temperature inhibits reproductive bud emergence, which occurs until the temperature reached 29°C/19°C. Experiment II further showed that plants needed to be kept at 29°C/19°C for nine weeks for reproductive bud emergence. Thus, 29°C/19°C may be the minimum required temperature for reproductive bud emergence, while 32°C/22°C is the optimal temperature for reproductive bud development and emergence in white-fleshed pitaya. These findings suggest that the induction of reproductive buds in pitaya is first initiated under a long-day photoperiod, but warmer temperatures are required for their subsequent emergence. This study also evaluated how high temperatures affect flowering, fruiting, and cladode yellowing of the high-temperature sensitive red-fleshed pitaya ‘Da Hong’ under controlled conditions. The studies were conducted in the phytotron at high-temperature (HT, 40°C/30°C), moderated high-temperature (MH, 35°C/25°C, 2017), and optimal temperature (CK or OT, 30°C/20°C) in 2015 and 2017. The duration from floral bud emergence to bloom decreased as the temperature increased. Flower length was shorter under HT condition than OT and MH. The in vitro pollen viability at OT, MH, and HT was 65.1%, 8.9%, and 0.6% indicating that higher temperature caused pollen sterility. The mutual cross could evaluate the female organ’s sterility with the pollen and pistil from the three treatments. The fruit set, fruit weight, and seed weight were only 16.7%–29.2%, 72.1–110 g and <1g from HT self-pollination. However, pollination under HT with higher-viability pollen could recover the fruit set in 100%, the fruit weight and seed weight increased as well. The recovery fruit set means the female maintain better function than the male under HT. To cross OT pollen with MH pistil or self-pollination did not affect the fruit growth; thus, the female function under MH was not different from OT. Because of the high light intensity before the treatment, the shoot’s abaxial end showed yellower coloration and lower Fv/Fm than the adaxial end. The shoot regreening was performed one week after all treatments, but the HT shoot maintained a yellower coloration than the other treatments. The Fv/Fm variation responded at two weeks after treatments. The Fv/Fm under MH and OT recovered to 0.83 as the healthy plants. However, Fv/Fm in both the abaxial and adaxial ends of the shoot decreased continuously until the experiment, thus, indicating that the PSII efficiency may decline during the HT period. Five lines with chilling tolerance of pitaya were selected during severely cold wave in January 2016. The cutting of five lines with chilling tolerance and four non-chilling-tolerant cultivars were transferred to the cold chamber at 6°C and 25°C. The shoot color was recorded as the a* and b* value using a spectrophotometer, and Fv/Fm value was measured using Mini-PAM before treatment and at 0, 4, 8, 24, 72 h after treatment. The a* and b* values of shoot color under the two treatments were not significantly different after chilling, indicating that low temperature did not lead to the yellowed cuttings in pitaya. The Fv/Fm value of all cultivars (hybrids) decreased at 0 h after chilling treatment. However, chilling-tolerant hybrids maintained a higher Fv/Fm value than the non-chilling-tolerant cultivars at 0 h after treatment. The Fv/Fm value returned to the normal value at 4 and 72 h after chilling-tolerant hybrids and non-chilling-tolerant cultivars treatments, respectively. Thus, the physiologic index of chlorophyll fluorescence for screening chilling tolerance is available. In conclusion, the BBCH scale for red-fleshed pitaya was established and separated from the description of white-fleshed pitaya. Temperature regulated bud development and reproductive bud emergence under long-day photoperiod was proved. The reproductive only emerged when the temperature reached the optimum. That high-temperature caused low pollen viability resulting in smaller fruit production in summer was confirmed. The chilling tolerance indicator application for screening chilling tolerant line by chlorophyll fluorescence could improve breeding.
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