Bird‐Cherry Oat Aphid (Rhopalosiphum padi) Feeding Stress Induces Enhanced Levels of Phenolics in Mature Wheat Grains

Abstract

Enhancement of naturally occurring phenolic compounds with antioxidant activity in hard red winter wheat (Triticum aestivum L.) is a value addition strategy that can potentially increase the profitability of wheat crops. Phenolics are plant secondary metabolites known to be involved in defense against arthropods and pathogen attack. In this study, the effect of bird‐cherry oat aphid (Rhopalosiphum padi L.) feeding in wheat at different phenological stages on phenolic concentration in mature grains was investigated. Aphids were allowed to feed and reproduce for 14 d on wheat plants at the following stages of development: five tillers, 7 or 21 d postanthesis (DPA). Plants infested at the five‐tiller and 7‐DPA stages had higher free phenolic concentration than aphid‐free controls, and those moderately infested at five tillers through 35 DPA had significantly higher concentration of free and free and conjugated phenolics and 2,2‐diphenyl‐1‐picrylhydrazyl radical scavenging activity than aphid‐free controls (P < 0.0125). Although there were no significant differences among phenological stages, more resources were allocated to defense (i.e., free phenolic concentration) and less to growth (i.e., grain yield) when infestation started at early stages. The phenolic response was long lasting and systemic, so systemic acquired resistance was hypothesized to be the mechanism of induction. This information will aid in developing wheat crops with consistently high antioxidant levels.