Sites of Ozone Sensitivity in Diverse Maize Inbred Lines

Tropospheric ozone (O₃) is an air pollutant that costs ~$14-26 billion in global crop losses and is projected to worsen in the future.  Potential sites of O₃ sensitivity in maize were tested by growing 200 inbred lines, including the nested association mapping population founder lines, under ambient (~40 ppb) and elevated O₃ concentrations (100 ppb) at the Free Air Concentration Enrichment (FACE) site in Champaign, IL.  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, O₃ accelerated the time to anthesis and silking by ~1 day, but did not affect the anthesis to silking interval. Elevated O₃ 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 O₃. Elevated O₃ reduced incidence of common rust on leaves at flowering, but increased incidence of stalk rot at harvest in some lines.  Analysis of leaf and silk biochemistry, leaf reflectance, stomatal patterning and yield is ongoing.  There appear to be many sites of O₃ sensitivity in C4 maize, and significant genetic variation in O₃ responses in all phenotypic traits examined.  Future work will investigate O₃ tolerance in both inbred and hybrid maize lines, identify phenotypic traits with the strongest correlations to yield loss, and identify O₃ tolerant and sensitive maize germplasm.