Priming of rice (Oryza sativa L.) seedlings with abscisic acid enhances seedling survival, plant growth, and grain yield in saline-alkaline paddy fields

Saline-alkaline (SA) stress is one of the major constraints to crop production worldwide. It is characterized by high salinity and high alkalinity (high pH), with the latter being the primary inhibiting factor to rice growth. We previously reported that pretreatment with abscisic acid (ABA) primed rice seedlings for enhanced tolerance to alkaline stress. In the present study, we conducted a 3-year field experiment to further assess the ABA-priming effect on the stress tolerance of rice plants in two paddy fields with different SA levels (field-A: non-reclaimed field, pH = 10.13 ± 0.009, EC1:5 = 0.50 ± 0.004; field-B: reclaimed field, pH = 9.74 ± 0.005, EC1:5 = 0.48 ± 0.001). Rice seedlings were treated with ABA at concentrations of 0 (control), 1, and 10 μM by root-drenching for 24 h prior to transplanting to the two paddy fields with different SA levels. Compared to the control treatment, ABA application substantially reduced the occurrence of leaf withering by 22%-50% and seedling death by 11%-17%. Further, ABA application also significantly improved subsequent plant growth and the final grain yield by 8%-55%; a more profound effect was observed in the harder SA field. Expressions of the ABA-responsive genes SalT and OsWsi18 were highly induced by ABA treatment, and the induced levels were sustained until at least 8 d after transplanting. Collectively, these results suggest a potent priming effect of ABA on the SA stress tolerance of rice plants, providing an effective and practical approach to improving rice production in SA paddy fields.