Resilience of rice (Oryza spp.) pollen germination and tube growth to temperature stress

Abstract

<p><b>Resilience of rice cropping systems to potential global climate change will partly depend on the temperature tolerance of pollen germination (PG) and tube growth (PTG). Pollen germination of high temperature-susceptible <i>Oryza glaberrima</i> Steud. (cv. CG14) and <i>Oryza sativa</i> L. ssp. indica (cv. IR64) and high temperature-tolerant <i>O. sativa</i> ssp. aus (cv. N22), was assessed on a 5.6–45.4 °C temperature gradient system. Mean maximum PG was 85% at 27 °C with 1488 μm PTG at 25 °C. The hypothesis that in each pollen grain, the minimum temperature requirements (<i>T</i>_n) and maximum temperature limits (<i>T</i>_x) for germination operate independently was accepted by comparing multiplicative and subtractive probability models. The maximum temperature limit for PG in 50% of grains (<i>T</i>_x(50)) was the lowest (29.8 °C) in IR64 compared with CG14 (34.3 °C) and N22 (35.6 °C). Standard deviation (<i>s</i>_x) of <i>T</i>_x was also low in IR64 (2.3 °C) suggesting that the mechanism of IR64's susceptibility to high temperatures may relate to PG. Optimum germination temperatures and thermal times for 1 mm PTG were not linked to tolerating high temperatures at anthesis. However, the parameters <i>T</i>_x(50) and <i>s</i>_x in the germination model define new pragmatic criteria for successful and resilient PG, preferable to the more traditional cardinal (maximum and minimum) temperatures.</b></p>