Plant growth regulators control ozone damage to wheat yield

•   Tropospheric ozone (O₃ ) is damaging to plants and decreases crop yields. This study investigated the role of two plant growth regulators in affecting wheat-yield responses to elevated [O₃ ]. In a controlled factorial experiment, wheat plants were treated with combinations of Ethephon, which releases ethene, Chlormequat, which blocks gibberellin synthesis, and elevated [O₃ ]. •   Spring-wheat plants were subjected to lifelong exposures to ambient or moderately elevated [O₃ ]. At flag-leaf emergence, the plants were treated with Ethephon and/or Chlormequat, or untreated (controls). Gas-exchange measurements were made at anthesis; morphology, biomass, and yield components were recorded at harvest. •   Elevated [O₃ ] accelerated development and decreased the number of grains per ear and ears per plant. Chlormequat abolished these O₃ effects, protecting against yield reduction though not biomass loss. Ethephon treatment partially protected against O₃ -induced biomass loss though not yield reduction. •   This study suggests that the effects of elevated [O₃ ] on development and allocation are more important in determining the yield response of wheat than the accompanying decline in photosynthesis and biomass accumulation.