Lack of a synergistic interaction between ozone and wheat leaf rust in wheat swards

Ozone is an air pollutant regulated in the USA under the Clean Air Act. Increasingly, concerns have been raised regarding the interactions between ozone and pests, pathogens, and plant competition. This study was conducted to improve our understanding of plant responses to ozone in the presence of pathogens, and specifically to determine the effect that wheat leaf rust and ozone exposure had on wheat productivity. The study was conducted in open-top ozone exposure chambers in Corvallis, OR, using two cultivars of spring wheat (Twin and Yecora Rojo). Twin was grown at two densities. Two levels of ozone and three levels of disease were applied in all combinations, for a total of six treatments. The treatments were replicated twice and repeated over 2 years. Disease severity readings were taken three or four times during each growing season. At the completion of grain-fill, the plants were removed from the chambers and harvested. Wheat height and above-ground biomass generally decreased with ozone exposure and with increasing disease severity in both years, while total grain weight decreased significantly only with disease in 1997. There was no interaction between ozone and disease, regardless of cultivar, density, or the plant response variable measured. There was little evidence that ozone exposure affected the severity of wheat leaf rust.