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Jer-Chia Chang and Tzong-Shyan Lin

The goal of this study was to document the relationship between fruit growth patterns and flushing number in litchi (Litchi chinensis Sonn. cv. 73-S-20). The impact of flush number on fruit retention, fruit quality, and leaf efficiency (g fruit FW produced per unit of leaf area at harvest) was assessed in field-grown 6-year-old trees by adjusting the number of flushes per bearing shoot through girdling at two fruit developmental stages. The cumulative fruit growth was sigmoidal. The greatest fruit relative growth rate (RGR) occurred during 3 to 5 weeks after full bloom (AFB), peaking on week 3 at 0.39 g·g−1 dry weight (DW) per day. The greatest fruit absolute growth rate (AGR) occurred during weeks 8 to 11, peaking on week 11 at 0.16 g·d−1 DW. Fruit retention was sensitive to girdling applied during week 3. Most fruit dropped on branches with ≤ two flushes, whereas fruit continued to develop on branches with three flushes and on the controls. There was a gradual loss of fruit when the girdling was applied during week 8. The number of fruit retained on branches with two and three flushes was similar to the controls. At harvest, regardless of the time of branch girdling, fruit yield and quality increased with increasing number of flushes; shoots with three flushes were similar to ungirdled controls. Leaf efficiency on branches girdled during week 3 was inferior to that girdled during week 8. All treatments had similar leaf efficiency when branches were girdled during week 8. On the other hand, girdling treatment applied during week 3 resulted in variable leaf efficiency among treatment, indicating that fruit were utilizing reserves in bearing shoots. We concluded that bearing shoots of ‘73-S-20’ litchi trees require a minimum number of three flushes for adequate fruit production.

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Yu-Chun Chu, Tzong-Shyan Lin, and Jer-Chia Chang

In this study, we documented whether pollen parents are required for fruiting and their effects on fruit set and seed characteristics in field-grown ‘73-S-20’ litchi (Litchi chinensis Sonn.). The effects of preventing female (F) flower pollination to induce parthenocarpy, selfing, and outcrossing with ‘Haak Yip’ and open-pollinated (OP) fruits derived from F flowers and the second wave of the male (M2) flowers of ‘Haak Yip’ blooming in synchrony were assessed. The correlation between the percentage of fruit set and shriveled seed/seed weight in self-crossed and outcrossed fruits was calculated. At harvest, the absence of pollination induced a high proportion of parthenocarpic fruit without seed, although the fruit weighed only 4.2 g. Fruit set with outcrossing was greater than that with selfing and the percentage of shriveled seed obtained in self-crossed fruits was much greater than that in outcrossed fruits but not different from that in OP fruits, suggesting that outcrossing increased but selfing decreased the cluster yield and seed weight. However, 33.3% and 23.0% of seed contained embryos in selfed and OP fruits, respectively. No positive correlation between the percentage of fruit set and shriveled seed/seed weight was found, indicating that seed abortion during development was not the key factor leading to low yield. We concluded that tiny parthenocarpic fruit could be obtained but that pollination is essential for the good yield of ‘73-S-20’. Outcrossing markedly increased fruit set and seed weight and decreased the percentage of shriveled seed. Factors other than the pollen parents may be involved in the seed development of ‘73-S-20’.

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Yi-Lu Jiang, Tzong-Shyan Lin, Ching-Lung Lee, Chung-Ruey Yen, and Wen-Ju Yang

Yellow pitaya, Selenicereus megalanthus (Schum. ex. Vaupel) Moran, is a potential new fruit in Taiwan. It sprouts mostly in winter and flowers in late spring and fall. In this study, an average of 60% shoots within canopies flowered. Shoots sprouted in the current winter flowered in fall and produced winter fruits, and shoots sprouted earlier than the current winter flowered in late spring and produced summer fruits. Floral buds on most shoots appeared at the distal end. The weight, pulp percentage, and total soluble solids of winter fruits were significantly higher than those of summer fruits. The number of black seeds was positively correlated with pulp weight (R 2 = 0.87). The total soluble solids in the core region of winter fruits reached 22.7 °Brix, higher than that in other regions. Future efforts to improve yellow pitaya production in Taiwan include increasing winter fruit production by enhancing growth of the current year's new shoots through proper canopy management and increasing the size of summer fruit by artificial pollination, fruit thinning, and other means.

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Yi-Lu Jiang, Yuan-Yin Liao, Tzong-Shyan Lin, Ching-Lung Lee, Chung-Ruey Yen, and Wen-Ju Yang

Red pitaya (Hylocereus sp.), which flowers between May and October and sprouts between November and May in Taiwan, has been confirmed to be a long-day plant. The areoles on the old shoots may be induced to flower after the March equinox naturally, and the floral bud formation occurs in two to three waves from May to October. We conducted experiments on photoperiodic regulation of floral bud formation from June to Dec. 2009 and tested the feasibility of off-season production in 2011. Shortening summer daylength to 8 h inhibited the areoles at the distal end of the shoots to develop into floral buds and promoted sprouting at the proximal ends of the shoots. Night-breaking treatment between the September equinox and the winter solstice led to floral bud formation. The critical daylength seemed to be ≈12 h, and night-breaking treatment would be applicable between the September and the next March equinoxes to produce off-season crops. The duration of night-breaking required for flower differentiation was longer in the cooler than in the warmer season. Four weeks of night-breaking treatment was sufficient to promote flowering in late fall (mid-October to mid-November), but 3 months were required to generate similar result in the winter and early spring (January to March) in southern Taiwan.