Photosynthesis and related gas exchange traits in rice subspecies under high temperature environment

High temperature is one of the major abiotic stresses that limits rice productivity. Rice is majorly grown in Asian countries located in the tropics and subtropics, where the crop experiences higher temperatures during the crop season. Global warming can further accelerate the temperature above the current level and could be detrimental to the photosynthetic process of the rice crop. The current study reports the effects of high temperature stress (HT) on photosynthesis and related traits in two rice subspecies ( Indica and Japonica ). Fourteen rice accessions representing both subspecies were raised in a normal environment till booting and later exposed to HT in a greenhouse, till physiological maturity. The present study showed that exposure to increase in growth temperature (HT, 38 °C) had negatively affected the photosynthetic rate ( Pn ) in both the rice subspecies and the highest reduction was recorded in the Japonica subspecies compared to Indica . On the other hand, transpiration rate ( E ) and stomatal conductance ( gS ) showed an increasing trend and a weak correlation between dry shoot weight and Pn was recorded among both the subspecies. There was significant variability for Pn and other gas exchange traits in both the rice subspecies and Indica performed better than Japonica in hot environments. The study concludes that wild relatives and landraces of both rice subspecies may be exploited for variability in the rate of photosynthesis and related gas exchange traits to identify novel QTLs/alleles for future rice breeding programs.