| Summary: | 碩士 === 中興大學 === 園藝學系所 === 102 === ''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&;#8804;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&;#8804;0.05). Leafless inflorescence exhibited significantly higher number (P&;#8804;0.05) and ratio of fruit set (P&;#8804;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&;#8804;0.05); however, pulp percentage and TSS content were significantly highest in shriveled-seeded fruit(P&;#8804;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&;#8804;0.05); while pulp percentage was negatively correlated (r= -0.42, P&;#8804;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.
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