Effects of exogenous abscisic acid, gibberellic acid, auxin and zeatin on Fusarium graminearum infection in wheat

The classical roles of phytohormones in plant defense are generally well defined. However, very few of these have been reported with respect to Fusarium head blight (FHB) in wheat. Here, the association between an array of phytohormonesand FHB pathogenesis is investigated. Initial experiments in which hormones were co-applied to the wheat head with F. graminearum inoculation, showed that while zeatin and auxin had little impact, ABA or GA co-application increased and decreased FHB spread respectively. These phytohormone induced effects may be attributed to alteration of the F. graminearum transcriptome, as a high throughput RNASeq analysis of the treated plants showed that ABA promoted expression of early-infection genes including hydrolases and cytoskeletal reorganization genes, while GA suppressed the expression of nitrogen metabolic genes in the pathogen. On the other hand, neither ABA nor GA elicited significant effects on F. graminearum fungal growth or sporulation in axenic conditions in shake flask cultures, nor do these phytohormones affect trichothecene gene expression, deoxynivalenol mycotoxin accumulation, or SA/JA biosynthesis in F. graminearum-challenged wheat spikes. Overall we conclude that GA and components of its associated metabolic and signaling pathways may serve as effective priming agents, and genetic targets in breeding programs against FHB. However, additional investigations of the impact of the co-application of GA on the wheat transcriptome will be essential, and are ongoing at this time.