Pollen quality and performance in strawberry plants exposed to high-temperature stress

Abstract

The effects of high-temperature stress on pollen viability and in vitro and in vivo germinability were studied in two facultative, short-day strawberries (Fragaria xananassa Duch.), 'Nyoho' and 'Toyonoka.' Plants were exposed to two day/night temperature regimes of either 23°C/18°C (control) or 30°C/25°C (high temperature) from when the first inflorescence became visible until anthesis. Pollen viability in 'Nyoho' was only slightly affected at 30°C/25°C when compared with pollen from plants grown at 23°C/18°C. In 'Toyonoka', however, pollen viability was significantly lower at 30°C/25°C than at 23°C/18°C. The in vitro germination percentages were significantly lower in pollen from plants grown at 30°C/25°C and germinated at 30°C than from plants grown at 23°C/18°C and germinated at 23°C in both cultivars. But the percentages were much lower in 'Toyonoka' than in 'Nyoho', particularly at the 30°C germination temperature. Pollen from plants grown at 23°C/18°C also extended longer pollen tubes than pollen grown at 30°C/25 °C in both cultivars, but 'Nyoho' had longer pollen tubes than 'Toyonoka' at 30°C/25°C. Fluorescence microscopy revealed that most of the 'Nyoho' pollen germinated on the stamen, elongated through the style and reached the ovule regardless of temperature treatment. In 'Toyonoka', pollen germination and elongation were greatly inhibited at 30 °C/25°C, resulting in unfertilized ovules. These results suggest that certain strawberry cultivars produce heat-tolerant pollen, which in turn could result in higher fruit set.