PERTANIKA JOURNAL OF SCIENCE AND TECHNOLOGY

Rice (Oryza sativa L.) ‘KDML105’ is the most popular aromatic rice originating in Thailand. This cultivar is highly susceptible to abiotic stresses, especially drought and salt stress during the seedling stage. The objective of this study was to investigate the photosynthetic performance in response to drought and salt stress of four improved breeding lines, specifically CSSL94 and CSSL103 (containing drought-tolerant quantitative trait loci: DT-QTLs) and RGD1 and RGD4 (containing a salt-tolerance gene, SKC1), with ‘KDML105’ (susceptible) and DH103 (tolerant to drought and salt stress) as the controls. Rice seedlings were grown for 21 days in hydroponic solutions and then exposed to salt stress (150 mM NaCl) or drought stress (20% PEG6000) for 10 days. The results indicated that when subjected to drought and salt stress, all rice lines/cultivar exhibited significant reductions in net photosynthesis rate (P_N), stomatal conductance (g_s), transpiration rate (E), the maximal quantum yield of PSII photochemistry (F_v/F_m), the effective quantum yield of PSII photochemistry (F_v’/F_m’), photosynthetic pigments, and SPAD readings, whereas water use efficiency (WUE) and non-photochemical quenching (NPQ) increased. Compared with ‘KDML105’, CSSL94, and CSSL103 were more tolerant to both drought and salinity, showing less reduction in all photosynthetic parameters. For RGD1 and RGD4, it was confirmed that these lines had a higher level of salt tolerance than ‘KDML105’ based on better photosynthetic performance under salt stress, demonstrating that these lines were also more tolerant to drought stress.