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

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 O ryza glaberrima   S teud. (cv. CG 14) and O ryza sativa   L . ssp. indica (cv. IR 64) and high temperature‐tolerant O . sativa ssp. aus (cv. N 22), was assessed on a 5.6–45.4 ° C temperature gradient system. Mean maximum PG was 85% at 27 ° C with 1488  μ m PTG at 25 ° C . The hypothesis that in each pollen grain, the minimum temperature requirements ( T n ) and maximum temperature limits ( T x ) for germination operate independently was accepted by comparing multiplicative and subtractive probability models. The maximum temperature limit for PG in 50% of grains ( T x(50) ) was the lowest (29.8 ° C ) in IR 64 compared with CG 14 (34.3 ° C ) and N 22 (35.6 ° C ). Standard deviation ( s x ) of T x was also low in IR 64 (2.3 ° C ) suggesting that the mechanism of IR 64'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 T x(50) and s x in the germination model define new pragmatic criteria for successful and resilient PG , preferable to the more traditional cardinal (maximum and minimum) temperatures.