Phloem-feeding insect infestation antagonizes volatile organic compound emissions and enhances heat stress recovery of photosynthesis in Origanum vulgare

Abstract

Heatwaves are expected to become more frequent and directly exert major stress on plants. Warmer weather can also increase the frequency of biotic infestations. However, how biotic stress alters heat resistance and how interacting heat and biotic stresses alter volatile organic compound (VOC) emissions remain unclear. We studied how heat shock (45 ℃ for 5 min) and Trialeurodes vaporariorum infestation alone and in combination affect foliage photosynthetic characteristics and VOC emissions in Origanum vulgare, right after heat stress through 48 h recovery. Heat stress alone decreased photosynthesis rate (A) but increased stomatal conductance (gs), emissions of lipoxygenase pathway volatiles (LOX), benzenoids and terpenoids. Neither A nor VOC emissions recovered to pre-stress values at 48 h after stress application. Whitefly infestation reduced A and increased gs, and resulted in a moderate increase in terpene emissions, but inhibited constitutive LOX and benzenoid emissions. Heat stress applied on whitefly infestation reduced A and increased gs, and resulted in a much lower enhancement of LOX and terpene emissions. Photosynthetic characteristics fully recovered at 48 h after stress treatment. Our results suggest that under phloem-feeding insect herbivory, VOC emission responses to extreme temperature are highly desensitized and photosynthetic thermal tolerance is improved.