Following high summer temperatures in Taiwan, erratic fruit production and yellowed cladode have been observed in red-fleshed ‘Da Hong’ pitaya (Hylocereus polyrhizus). However, the specific environmental influences that result in the yield loss and cladode damage are unknown. The aim of this study was to evaluate how high temperature affects fruit production and cladode yellowing of ‘Da Hong’ pitaya under controlled conditions. One-year-old field-grown potted plants with moderately yellow-colored cladodes were placed in the phytotron at either 40/30 °C ± 1 °C [day/night, high-temperature treatment (HT)] or 30/20 °C ± 1 °C [day/night, control (CK)] during the natural long-day reproductive period. Floral bud development duration, flower opening behavior, fruit set and development, as well as fruit characteristics and seed setting (which was expressed as the estimated number of seeds), and the weight per fruit at harvest were investigated. In addition, the percentage of dry matter and color change (regreening) of cladodes were examined. We found that floral bud development was completed 8 days earlier than the control, but the time of blooming was 2 to 3 hours later within a day; and fruit set, fruit size, seed weight, and peel color were strongly suppressed in HT-treated plants compared with the control. Furthermore, both the estimated seed number and seed weight were positively correlated with fruit weight, suggesting that reduced seed setting and weight arising from incomplete fertilization in the HT plants may have resulted in fruit drop and smaller fruit. Although the color on the sunny (sun-exposed) side of the cladode remained yellow, the percentage of dry matter in the HT cladodes was not significantly different from the control, indicating that the yellow-colored cladodes did not reduce their carbon supply potential. The results indicate that HT during bloom led to poorer fruit set and lower fruit weight, presumably due to lower seed setting/weight per fruit arising from incomplete fertilization. The HT treatment also caused less regreening of cladodes, but this did not seem to impact fruit production. Further study is required to ascertain whether disrupted stamens or pistils resulting from HT treatment lead to incomplete fertilization.
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’.