Sites of Sensitivity to Oxidative Stress from Ozone Exposure in Diverse Maize Inbred Lines

Tropospheric ozone is an air pollutant that costs ~$14-26 billion in global crop losses and is projected to worsen in the future.  Potential sites of ozone sensitivity in maize were tested over two years under ambient (~40 ppb) and elevated ozone concentrations (100 ppb) at the Free Air Concentration Enrichment (FACE) site in Champaign, IL.  In 2013, 200 inbreds, including the nested association mapping population founder lines, were screened. In 2014, 50 inbreds representing the extremes of ozone sensitivity were re-tested in addition to 26 hybrids. Ozone treated plants showed decreases in green leaf number and leaf chlorophyll and increases in leaf senescence compared to control plants, and these differences became progressively greater through the growing season. On average, ozone accelerated the time to anthesis and silking, but did not affect the anthesis to silking interval. Elevated ozone impaired spikelet formation in a subset of genotypes. Photosynthetic measurements of the reference line B73 revealed that daily C gain was reduced by >20% late in the season, showing that C4 photosynthesis is sensitive to ozone. Elevated ozone altered incidence of leaf and stalk diseases in a complex manner.  Analysis of leaf and silk biochemistry, leaf reflectance, stomatal patterning and yield is ongoing.  There appear to be multiples sites of ozone sensitivity in C4 maize, and significant genetic variation in ozone responses. Future work will investigate ozone tolerance, identify phenotypic traits with the strongest correlations to yield loss, and identify ozone tolerant and sensitive maize germplasm.