External application of phytohormones alters wheat resistance phenotype to Hessian fly under high-temperature stress

Heat stress can compromise plant resistance to insects. Overwhelming evidence has indicated that phytohormones salicylic acid (SA), jasmonic acid (JA), 12-oxo-phytodienoic acid (OPDA), and auxin play critical roles in plants’ responses to biotic and abiotic stresses. The objective of this research is to determine the impact of externally applied phytohormones on the wheat resistance phenotype of Hessian fly under heat conditions. To this end, we infested two Hessian fly resistant wheat cultivars, Molly, Iris, and a susceptible cultivar, Newton, with an avirulent Hessian fly biotype GP. The plants were sprayed with 2 mM SA, JA, OPDA, and indole acetic acid (IAA) solutions and their combinations, respectively, prior to heat stress of 35ºC for 24 hours. The resistance efficiency of plants in each treatment was measured and analyzed by comparing the percentage of susceptible plants and the percentage of live insects among treatments, respectively. Our results suggest that external application of phytohormones SA, JA, OPDA, IAA, and their combinations alter wheat's resistance efficiency to Hessian fly under heat conditions. Our finding sheds light on the mechanism of heat-induced loss of host plant resistance to insects.