Evaluation of the drought and salinity tolerance of Tai Nguyen rice seedlings through physiological, biochemical, and SSR marker analyses

Drought and salt stress are critical factors decreasing rice yields. In this study, we examined the physiological and biochemical responses to drought and salt treatments of Tai Nguyen (TN) rice seedlings, a developmental stage highly susceptible to environmental stresses. Additionally, simple sequence repeat (SSR) markers were employed to identify genetic differences between TN (survey) and Nipponbare (reference) cultivars. Our results demonstrated that the TN seedlings survived after 7 days of exposure to either 120 mM NaCl (salt stress) or 20% polyethylene glycol (PEG; drought stress), outperforming the Nipponbare cultivar. Physiological analyses revealed that drought stress predominantly impaired shoot growth, whereas salt stress inhibited both shoot and root development. Under both stress conditions, proline content increased progressively with escalating stress levels. In contrast, chlorophyll and carotenoid content increased in response to drought and decreased under salt stress (60 to 120 mM NaCl). Enzymatic assays indicated a 3-fold increase of ascorbate peroxidase (APX) activity with 20% PEG treatment, whereas guaiacol peroxidase (GPX) activity was significantly reduced by salt stress conditions. Moreover, superoxide dismutase (SOD) activity remained stable under drought but increased under salt treatments. SSR marker analyses identified genetic variants of TN in four drought-related SSR markers (RM164, RM223, RM228, RM263) and three salt-related Saltol SSR markers (RM493, RM562, RM3412), corresponding to insertions and deletions in the repeat regions. These findings indicate that TN is a promising rice cultivar for production in the Mekong Delta, where both drought and salt stress pose significant challenges.