Abstract: Drought tolerance (DT) or water-saving is becoming one of the most important target traits in rice breeding community under ever-increasing severe drought situation all over the world. The introgression line “PD29” with IR64 genetic background has promising yield performance under both drought (stress) and irrigation (control) conditions. In the present study, the physiological characteristics related to stress tolerance of the “PD29” were analysised with recurrent parent, IR64, and upland rice variety IRAT109 as control varieties under both drought and irrigation conditions. The results showed that “PD29” not only had higher leaf relative water content (RWC) under stress but also could recover RWC to a fully turgid (hydrated) state 2 h after re-watering which indicated that “PD29” has higher DT ability than control varieties at the tillering stage. Further analysis showed that “PD29” not only had higher maximum photochemical of FPS II efficiency (F_v/F_m), osmotic potential (Y), proline content (Pro), and antioxidants activity (AOA) than IR64 under drought condition but also presented less decrease in the F_v/F_m and RWC and more decrease in net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s) and more increase in Pro and AOA. Furthermore, compared to IRAT109, “PD29” had higher Pro and more increase in the AOA under drought condition. Therefore, it was concluded that the promising DT-performance of “PD29” was related to the significant increase of AOA and proline under the drought. Moreover, the significant decrease of the P_n, G_s, and T_r under the drought condition indicated that “PD29”has strong plasticity in photosynthetic capacity which can keep the higher photosynthesis under the adaptive circumstance and decrease the water loss through transpiration under the stress condition.

Key words: Rice, Drought tolerance, Photosynthesis, Plant water status, Antioxidant enzyme