Pollen Quality and Performance in Strawberry Plants Exposed to High-temperature Stress

in Journal of the American Society for Horticultural Science
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  • 1 Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan

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 ×ananassa 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.