Saponarin, a Diglycosyl Flavone from the Ancestral Wheat Triticum monococcum, Is an Allelochemical Reducing the Survival of Cereal Aphids

The English grain aphid (Sitobion avenae) and bird cherry-oat aphid (Rhopalosiphum padi) threaten wheat production through direct feeding and indirectly as virus vectors (e.g. barley yellow dwarf virus - BYDV). Aphid management still relies predominantly on insecticides, an increasingly unsustainable practice; however, host-plant resistance is a promising solution to manage aphids and the viruses that they transmit. Resistance has been recently identified in the ancestor wheat Triticum monococcum MDR045 and MDR049 against S. avenae and R. padi. In this study, we investigated whether foliar chemistry plays a role in this resistance against S. avenae. Foliar extracts from T. monococcum MDR045 and MDR049 reduced S. avenae survival in artificial feeding assays. Activity was aphid density-dependent and systemic responses were limited to the leaf of the aphid feeding site, following 24 h aphid herbivory. Bioassay-guided fractionation isolated saponarin, a di-glycosyl flavone, as an allelochemical involved in this activity. Saponarin activity was similar to naringenin, but unique compared to other plant flavonoids tested. Implications of these findings for effective aphid and virus management are discussed.