Résumé
Coping with heat stress involves different options that account for the ability of plants to escape (early anthesis time), avoid (panicle cooling through transpiration) or tolerate (presence of genes of interest) heat at flowering. First, variability in the time of day of anthesis was correlated with the mean of climatic variables calculated for the 7-day period before flowering, over four distinct seasons and four contrasted varieties. The best predictive variables (negative correlations) were Tmin and VPD, with high values of both being associated with early times. Second, depending on conditions, panicle temperature varied between 9°C below and 2°C above air temperature at 2 m. A significant positive correlation was obtained between spikelet sterility rate and maximum panicle temperature at flowering, whereas no correlation was obtained with air temperature. By extrapolation, this correlation predicted minimal sterility with a panicle temperature of 30 °C, and 50 % sterility with a panicle temperature of 33-34 °C. Third, a genome-wide association study of the sterility rate of 167 traditional and modern varieties (grown for six consecutive days at 37°C between 8 am and 2 pm at anthesis) detected 91 significant associations grouped into 12 independent regions located on eight chromosomes. The highest heat tolerance was detected for N22, an aus variety from India, and Peh Kuh, a traditional indica variety from Taiwan. Avoidance and tolerance appear as main genetic improvement pathways, whereas sensitivity of time of day of anthesis to air temperature and humidity seems already effective within the rice crop. (Texte intégral)