Characterizing the Role of Gibberellic Acid (GA) in Rice Defense Against Fall Armyworm (Spodoptera frugiperda) Feeding

Plants respond to insects through changes in defense response, which reduce insect fitness. Gibberellin (GAs) and jasmonate (JAs) pathways are two key pathways modulating antagonistically these responses. Gibberellic acid is a hormone involved in plant growth that has not been extensively studied in plant defense against insects, whereas JA is known to be implicated in plant defense responses. In this study, the effect of GA on resistance to fall armyworm (FAW) was compared in a commercial cultivar ‘Cocodrie’ and a GA mutant of the Shiokari cultivar ‘Super Dwarf’ deficient in GA production. To explore the effect of GA responses on the negative GA-JA interactions, a greenhouse experiment was conducted in plants treated with or without GA₃ to determine resistance to FAW by measuring the weight gains of larvae. Treatment with GA₃ resulted in a dose-dependent reduction in growth of FAW on the mutant line but no concentration effect was observed on the commercial line. Larval weight gain showed that GA₃ induced resistance to fall armyworm in the ‘Super Dwarf’ line. These findings suggest that GA may play a role in plant defense via signaling pathways in response to FAW feeding and suggest further studies of GA signaling in plant defense.