5. Abscisic acid (ABA) Abscisic acid (ABA) is a plant hormone that plays important roles in regulating drought, cold stress and osmotic stress responses. Moreover, it plays a role in promoting seed dormancy while antagonizing the growth-inducing effects of phytohormones like gibberellin (Ng et al., 2014). As described below, several studies have demonstrated a negative role of ABA in plant resistance against necrotrophic pathogens. As in the case of BRs, ABA interferes with the other hormone signaling pathways.