Low Night Temperature Inhibits Fertilization in ‘Monthong’ Durian (Durio zibethinus Murr.)

抄録

Durian is known to set fruit poorly or generate uneven-shaped fruits when exposed to temperatures below 20°C at anthesis. However, the effect of temperature on pollen-tube elongation during style or ovule development is not fully understood. In this study, the effects of temperature on pollen germination, pollen-tube elongation, and fruit set were investigated in ‘Monthong’ durian. First, pollen germination on agar media was tested at 10, 15, 20, 25, 30, and 35°C. Pollen-tube kinetics in emasculated fresh style was observed at the same temperatures until 48 h after pollination. At 20 and 25°C, more than 45% of pollen grains germinated throughout the 2-year observation period. At 20, 25, and 30°C, pollen tubes reached the base of the style within 48 h. Pollen-tube elongation was inhibited at 15 and 35°C. Next, the night (2000 to 0800 h) temperature around the flowers was fixed at 15 or 25°C for 7 nights in an orchard, after which pollen-tube elongation and ovule development at 7 days after pollination (DAP) were investigated. Pollen tubes reached the base of the style at both temperatures; however, at 15°C, ovules remained at the mature stage before accepting the pollen tube. Ovule development at 25°C progressed to the endosperm nuclei division stage, which was indicative of fertilization. Flowers or fruits abscised markedly at 15°C by 14 DAP. Based on these results, night temperatures below 15°C during anthesis inhibit fertilization in ‘Monthong’ durian. Additionally, flower abscission at 15°C was caused by failed fertilization.