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Effects of Structure, Types and Two Female Flowering Cycles of Reproductive Shoots on Fruit Production, and Study on Development of Seed and Embryo in 'Yu Her Pau' Litchi
|關鍵字:||荔枝;花序型態;花序結構;第一側花序;混合花序;兩波偏雌花;種子形態;液態胚乳;核型胚乳;游離胚;胚敗育;焦核率;果形指數;果實品質;絕對生長速率;相對生長速率;Litchi;Reproductive shoot types;Inflorescence structure;1st order paracladium;Mixed inflorescence;Two female flowering cycles;Seed morphology;Liquid endosperm;Nuclear type endosperm, Detached embryo (free embryo);Embryo abortion;Shriveled-seed ratio;Fruit shape index;Fruit quality;Absolute growth rate (AGR);Relative growth rate (RGR)||摘要:||
'Yu Her Pau' litchi (Litchi chinensis Sonn.) is an important early-maturing litchi cultivar in Taiwan. Although the production area has recently increased in relation to improvement of late-flushing avoidance, inflorescence-thinning manipulation, and plant growth regulator application, the fruit set percentage is still erratic, the impacts of two female flowering cycles on fruit quality and yield are unclear, and the shriveled-seeded ratio is unstable; however, so far, little or valid information is known. In the present study, we aimed to document and clarify the aspects mentioned above through following four investigations on 10-11-year old field-grown 'Yu Her Pau' trees cultivated in Fenyuan, Changhua in 2013 and 2014: 1) Effects of leafless inflorescence structure, including main axis and 1st order paracladium length (PL), on flower number, flower sex, and fruit set. 2) Effect of reproductive shoots types (leafless inflorescence and mixed inflorescences, MI) on flower sex, fruit set, and fruit quality. 3) Effects of two female flowering and fruiting cycles on fruit development and quality. Four types of inflorescence/cluster were investigated, e.g. 1st cycle fruits from one cycle only, FF (as control); 2nd cycle fruits from one cycle only, SF; 1st cycle fruits in two cycles inflorescence, FFT; and 2nd cycle fruits in two cycles inflorescence, SFT. 4) Seed and embryo sac development by paraffin- and hand-sectioning during fruit developing period, while fruit quality influenced by seed morphology, e.g. normal seed, small seed, and shriveled seed at harvest was also documented.
The length of main axis, longest PL and mean PL were 37.0±2.0cm, 19.5±2.3cm and 4.8±0.6cm, respectively. Total number of florets and percentage of female flower and fruit set were 5791±867, 7.2±0.9% and 4.2±1.3% in leafless inflorescence, respectively. Number of 1st order paracladium florets and female flowers were positively associated with PL, which R2 were 0.847and 0.724 in P≤0.05, respectively. After the main axis divided to three groups by nodes position from 1-4, 5-8, and 9 till end of axis, neither of which was significantly different in the ratio of female flower and fruit set.
The total number of florets, number of female flower, and its percentage in leafless inflorescence were 3947, 611, and 16.63%, significantly exceeded to 2382, 348, 12.14% of MI (P≤0.05). Leafless inflorescence exhibited significantly higher number (P≤0.05) and ratio of fruit set (P≤0.01), e.g. 14 and 2.2% than 4 and 1.2% of MI. There was no significant difference in neither the shape index nor the quality of any part of fruit at harvest. The results indicated the quality of inflorescence and fruit was little increased by mature leaves of MI, while the production was higher in leafless inflorescence.
The first cycle of blooming of female flower was three weeks earlier than 2nd cycle, while the duration required for fruit development was 14 and 12 weeks, respectively. Fresh weight (FW) and dry weight (DW) of mature fruit between 1st cycle of fruits (FF and FFT) and 2nd cycle of fruits (SF and SFT) appeared greater differences and were 37.61±0.97, 7.72±0.20g, and 25.17±0.80, 5.29±0.13g, respectively; however, fruit growth patterns, DW of all parts of fruit, and total soluble solid (TSS) content among treatments of FF, SF, FFT, and SFT were similar. The absolute growth rate (AGR) of fruit was higher in the 2nd cycle fruits, while relative growth rate (RGR) of fruit was higher in the in the fruits from on cycle only. The FW and DW of 1st cycle fruits were higher, and their growth duration was longer, consistent with the low temperature during peel and pulp cell division stage recorded, indicating a fruit sink strength occurred. With the increased temperature during pulp growth period of two-cycle fruits growing, not only the FFT and SFT did not retard the growth of fruit from one cycle only, in contrast, they promoted the assimilate driven to them.
Mature embryo sacs and nuclear type endosperm were visible at 2 and 11 days after full bloom (DAFB), and liquid endosperm were visible by naked eye at 2 weeks after full bloom (WAFB); they had all disappeared by 9 WAFB. Early heart stage of embryo, detached embryo (free embryo), and embryo maturation were visible at 15, 20, 70 DAFB, while shriveled seed and testa color-broke were also observed at 70 DAFB. Pulp development started at 7 WAFB till fruit harvest, while the TSS content increased from nine WAFB, and was desweeting at 14 WAFB. Fruit, peel, pulp, and seed weight, were 28.4, 5.5, 21.9, and 1.1 g, respectively, at fruit-maturing harvest in 2014, whereas pulp percentage and TSS content were 76.8% and 17.7%, respectively. Small-seeded and shriveled-seeded ratios were 24.7% and 17.3%, respectively. Fruit, peel, and seed weight of normal-seeded fruit were significantly higher than small- and shriveled-seeded fruit(P≤0.05); however, pulp percentage and TSS content were significantly highest in shriveled-seeded fruit(P≤0.05), and were 79.0±0.3% and 18.0±0.2%, respectively. Fruit, peel, and pulp weight, as well as TSS content were positively correlated to seed weight in shriveled-seeded fruit (r=0.49-0.64, P≤0.05); while pulp percentage was negatively correlated (r= -0.42, P≤0.05).
In conclusion, female flower and fruit set ratios were seldom associated with the 1st order paracladium position within leafless inflorescence, while leafless inflorescence had higher fruit yield than that of MI, implying that removal of growing and young leaves of MI would be necessary to enhance fruit production. Two cycle fruits do not affect their growth patterns of any one of the fruits, but it declines the fruit size of SF and SFT, and lengthens the time to harvest of FF and FFT, making it inconvenient for grower to pick the fruit. The quality of shriveled-seededed fruit is superior to normal-seededed and small-seededed fruit due to its greatest sweetness and edible portion, while free embryo was observed during 2-3 WFAB, indicating that an indirect clue related the occurrence of shriveled seed is available, but the substantial mechanism is still unclear. Further studies to the causes resulting in embryo degeneration may be needed for the successful implementation of variation in seed morphology of 'Yu Her Pau' litchi.
'玉荷包'荔枝(Litchi chinensis Sonn. cv. Yu Her Pau)為台灣重要的早熟種荔枝，近年因秋冬季控梢 疏花序(inflorescence thinning)與生長調節劑施用等技術增進、，而使栽培面積及產量攀升，然仍有著果率、焦核率(shriveled-seeded ratio)不穩及花序上兩波果實共存(two fruiting cycles)之問題，相關文獻尚仍不足以解釋其肇因為何及如何改善，此等遂成為學界矚目及亟待探討之焦點。
有鑑於此，本研究以彰化縣芬園鄉簡氏 10-11 年生'玉荷包'植株為材料，於2013、2014 年 1-6 月評估：1) 純花序(leafless inflorescence)結構(包含花序主軸，main axis 與第一側花序長度，1st order paracladium length (PL))對花數、花性與著果之影響；2) 花序型態(區分為純花序及帶葉之混合花序，mixed inflorescence(MI))對花性、著果與果實品質之影響；3)同一花序上，兩波偏雌花、果實共存(區分為僅有第一波果實者 FF、僅有第二波果實者 SF、兩批次果實之第一波果實FFT 與兩批次果實之第二波果實 SFT)與否，對果實生育及品質之影響；及 4)石蠟與徒手切片觀察種子與胚囊發育過程 調查果實品質並區分大核(normal seed)、小核(small seed)與焦核果，比較三者果實品質差異與相關性等四個試項，建立'玉荷包'攸關開花與結實之重要生理資料，供後續研究及栽培原理之參考。
純花序之平均花序主軸長、最大 PL 與平均 PL 分別為 37.0±2.0、19.5±2.3 與4.8±0.6cm 總花數 偏雌花率與著果率分別為 5791±867 朵 7.2±0.9%與 4.2±1.3%。PL 對 各 側 花 序 之 總 花 數 與 偏 雌 花 數 具 高 正 相 關 性 (R2=0.847 and 0.724,respectively)。依花序主軸節位區分為第一至四節、第五至八節與第九節以上等三群，三群節位之偏雌花比率與著果率差異不顯著。純花序之總花數 偏雌花數與偏雌花比率高於 MI (P≤0.05) 分別為 3947 朵、611 朵 16.63%和 2382 朵 348 朵 12.14% 而其著果數(P≤0.05)與著果率(P≤0.01)，表現亦高於 MI，分別為 14 顆、2.2%與 4 顆、1.2%。惟果形指數(fruit shape index)與整體果實品質無差異 指出 MI 成熟葉片的存在不會提高'玉荷包'荔枝花序及果，實的品質表現，惟純花序之果實的生產能力較高。
同一花序上，第一波與第二波偏雌花之盛花時間相差三週，而其果實發育所需時間分別為 14 週與 12 週。第一波果實(FF 及 FFT)與第二波果實(SF 及 SFT)平均鮮乾重分別為 37.61±0.97、7.72±0.20 g 與 25.17±0.80、5.29±0.13 g，兩波果實鮮乾重相差 49%與 46%。四種果實發育過程(growth pattern)、各部位乾重佔果實的比例與總可溶性固形物(total soluble solid, TSS)含量皆相仿。第二波果實絕對生長速率(absolute growth rate, AGR)高於第一波果實；僅有一波果實(FF 與 SF)之相對生長速率(relative growth rate, RGR)則高於兩波果實(FFT 與 SFT)。第一波果實鮮乾重高於第二波果實，且發育時間亦長，與果皮及果肉(pulp or aril)發育期之環境低溫增加細胞分裂有關，顯示其有較高的積貯強度(sink strength)。第二波果實鮮乾重小於第一波果實，乃因著果至果肉發育期前，環境高溫減少果皮與果肉細胞數所致。
盛花後 2 與 11 天，可見成熟胚囊(embryo sac)與核型胚乳(nuclear typeendosperm)組織，液態胚乳(liquid endosperm)則於盛花後兩週起可被目視，迄第九週消失。盛花後 15 天與 20 天可見初期發育之心臟型胚(heart stage embryo)與胚游離(detached embryo or free embryo)現象，而胚於盛花後十週發育成熟。焦核種子與種皮轉色(testa color-broke)亦於盛花後第十週確定，種子則於盛花後第 11週成熟。果肉於盛花後七週開始生長至採收結束，盛花後九週起可測得 TSS 含量變化，盛花後 14 週則有退甘(desweeting)現象。2014 年成熟果實之果重、果皮重、果肉重、種子重、果肉率與 TSS 含量，分別為 28.4、5.5、21.9、1.1 g 與 76.8%、17.7%。小核與焦核率為 24.7%與 17.3%。大核果之果實、果皮與種子重高於小核與焦核果(P ≤0.05)，然焦核果有最高之果肉率(pulp percentage)與 TSS 含量，為79.0±0.3%與 18.0±0.2%。焦核果之種子重與其果重、果皮重、果肉重及 TSS 含量具正相關(r=0.49-0.64, P ≤0.05)，而與果肉率呈負相關(r= -0.42, P ≤0.05)。
經本研究可知，'玉荷包'純花序之偏雌花比率與著果率不因花序之位置而異，果實生產能力則高於 MI，果農常將帶葉之 MI 除葉可能為必要之手段。同一花序上 兩波果實共存不影響彼此之發育過程(growth pattern) 惟第二波果實較小，產期較慢，將造成採收之不便。焦核果之果重雖較大核與小核果為低，但因較小之種子與較高之果肉率、TSS 含量，其鮮食品質較優；種子焦核應與盛花後 2-3週游離胚的產生有關，其原因尚待進一步探討。
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