Heat Stress Leads to Poor Fruiting Mainly Due to Inferior Pollen Viability and Reduces Shoot Photosystem II Efficiency in “Da Hong” Pitaya

Yu-Chun Chu,Jer-Chia Chang

doi:10.3390/agronomy12010225

Abstract

High summer temperatures (day/night: 40 °C/30 °C) are known to cause poor fruiting, reduced fruit/seed weight, and delayed fruit development in the “Da Hong” red-fleshed pitaya (Hylocereus polyrhizus); however, the mechanisms of these effects are unknown. This study examined how high temperature (HT, 40 °C/30 °C) affects stamen and pistil fertility through pollination combinations and fruit set in “Da Hong” pitaya and evaluated photosystem II (PSII) efficiency in yellowed shoots (cladodes). The in-vitro pollen germination rate was significantly higher at optimal temperature (OT, 30 °C/20 °C) than at HT, which was also associated with a reduced flower length, poor fruit set, small fruit size, and low number of seeds after self-pollination. Meanwhile, fruit set and fruit development were remarkably improved by using the pollens taken from plants grown at OT and moderate temperature (MH, 35 °C/25 °C) after mutual cross pollination, indicating that the reduction in seed number caused by incomplete fertilization due to inferior pollen viability was the main cause of poor fruiting under HT rather than pistil or photoinhibition, although HT treatment was linked to reductions of PSII efficiency at both the adaxial and abaxial ends of shoots. The results suggested that pollen viability was most affected under HT stress; thus, yielding remarkably reduced fruiting.

Highlights

The pitaya (Hylocereus spp.) is an emerging fruit crop of the Hylocereus genus in the family Cactaceae
The red-fleshed pitaya “Da Hong,” which is sensitive to high temperature (HT), was selected as the plant material, and the study was performed in the Kaohsiung District Agricultural Research and Extension Station (KDARES), Changzhi Township, Pingtung, southern Taiwan (22◦41 N, 120◦31 E) using 2–3-year-old plants, which were planted in cutting pairs in 15-L pots supported by bamboo poles
The present study confirmed that fruit drop and the obstruction of fruit set and small fruit produced under HT during the period from floral development to fruit maturation of “Da Hong” pitaya is mainly caused by reduced pollen viability, as opposed to reduced photosystem II (PSII) efficiency

Summary

Introduction

The pitaya (Hylocereus spp.) is an emerging fruit crop of the Hylocereus genus in the family Cactaceae. Pitaya has been cultivated economically for >30 years, and it is currently a global economic fruit crop primarily cultivated in Southeast Asian countries, including Vietnam, Taiwan, Indonesia, Malaysia, and China’s Guangxi and Hainan provinces [2,3]. It is cultivated at a small scale in Israel, Nicaragua, Colombia, and Mexico. In Israel, high summer temperatures of up to 38 ◦C result in the production of 3–4 waves of flowers (a plant flowers 3–4 times during the reproductive period), and in some areas of extreme heat (44–46 ◦C), only one wave of flowers can be produced, in September, resulting in significantly reduced production [5]

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