Evaluation of S7, a synthetic partial abscisic acid agonist, as a potential suppressor of pre-harvest sprouting in rice

BACKGROUND: Pre-harvest sprouting (PHS) is a major constraint affecting grain quality and yield in rice, and its incidence is expected to increase with more frequent rainfall events associated with climate change. Although chemical control of PHS has largely focused on abscisic acid (ABA)-dependent regulation of seed dormancy and germination, the practical application of ABA is limited by its high cost and instability. This study investigated the potential of S7, a synthetic partial ABA agonist, as a chemical tool for suppressing PHS in rice. RESULTS: Germination assays, controlled-environment pot experiments, molecular analyses, and field trials were conducted to evaluate the physiological and molecular responses to S7 and its agronomic applicability. S7 treatment delayed seed germination and reduced α-amylase activity, thereby suppressing PHS, without increasing endogenous ABA levels during seed imbibition. Gene expression analyses showed that S7 treatment was accompanied by ABA signaling-related transcriptional changes, including early induction of OsABI4 and reduced OsGAMYB expression, together with reduced α-amylase activity. Controlled-environment pot experiments indicated that the suppressive effect of S7 depended on application timing during grain filling, whereas field trials supported its potential effectiveness under variable phenological and grain-filling conditions. CONCLUSIONS: These findings suggest that S7-mediated suppression of germination is associated with ABA signaling-related transcriptional responses rather than increased endogenous ABA accumulation. Overall, S7 may serve as a potential non-genetic chemical tool for reducing pre-harvest sprouting in rice, although further studies are required to optimize concentration, application timing, formulation, environmental stability, and cultivar-specific responses under field conditions.