| A two factorial (Ozone level×variety) study was done in a FACE system (free air ozone concentration enrichment) established in Xiaoji Town, Jiangdu County, Jiangsu Province, China (119°42′0″E, 32°35′5″N), from 2007 to 2009, to investigate the effects of O3 levels on the grain yield and quality in different genotypes of wheat. The two O3 levels were ambient level and 1.5 ambient level. The five tested varieties were Yannong 19(strong-gluten wheat), Yangmai 16 and Jiaxing 002(medium-gluten wheat), and Yangmai 15 and Yangfumai 2(weak-gluten wheat). The main results were as follows.1. The grain yield of wheat was significantly reduced by 10.1% to 34.5% under the ozone stress. Yangmai 16, Yangfumai 2, and Yannong 19 were sensitive to O3 stress. Yangmai 15 and Jiaxing 002 were moderately tolerant to O3 stress. The effects of ozone stress on the number of wheat ear and grain per panicle varied between experimental years and varieties. Ozone stress significantly reduced 1000-grain weight by 10.2% to 29.5%. The interaction between ozone concentration and genotype on 1000-grain weight were found significant. The protein yield was significantly reduced by -2.6% to 29.7% under the ozone stress. The starch yield was significantly reduced by 12.04% to 36% under the ozone stress. 2. Under the ozone stress,the grain filling period was shortened and the average filling rate was decreased. The length, width, and the thickness of grain were shortened, leading to declined grain volume. The surface of grain became shrunk, and 1000-grain weight decreased as well. Under the ozone stress, the decline in 1000-grain weight was the decisive factor reducing grain yield.3. Under the ozone stress, protein content, including albumin, globulin, gliadin, and glutenin, increased significantly by 5.9% to 22.6%. There was an increase of 0.6% to 12.5% in albumin, 13.6% to 113.4% in globulin, 10% to 57.1% in gliadin, and 4.3% to 20% in glutenin. Under the ozone stress, the content and proportion of gliadin were increased. The increase in the contents of gliadin and glutenin was one of the factors leading to the increased protein content.4. The starch content was also significantly reduced by 1.7 to 5.1% under the ozone stress. The content of amylase decreased by 2.6% to 18.4%, the content of amylopectin increased by 3.6% to 8.0%, and the ratio of amylase to amylopectin increased. The decrease in starch content was mainly due to the bigger decrease in amylopectin than the increase in amylase content. The increase in protein content was mainly due to the decrease in starch content.5. The wet gluten content, sedimentation value, swelling power, the energy area, the resistance to extension, the ratio of the paste were increased under the ozone stress. Under the ozone stress, the dough development time, dough stability time, and the number of farinograph quality increased, which could be probably caused by the increase in protein content under the ozone stress. The content of damaged starch, hardness and flour extraction rate were decreased by the ozone stress. The peak viscosity, trough viscosity and final viscosity were decreased, probably caused by the decrease in starch content.6.Under the ozone stress, the protein content, wet gluten content, and the dough stability time of Yangmai 15 and Yangfumai 2 (weak-gluten wheat) increased and failed to meet the Chinese national standard which demand the protein content lower than 11.5%, wet gluten content lower than 22%, and dough stability time shorter than 2.5 min. However, the protein content, wet gluten content, and dough stability time of Yannong 19 (strong-gluten wheat), Yangmai 16 and Jiaxing 002 (medium-gluten wheat) were increased under the ozone stress, and met the Chinese national standard. Consequently, the nutritional quality of weak-gluten wheat was deteriorated, and the nutritional quality of strong-gluten wheat and medium-gluten wheat was improved. But 1000-grain weight was significantly reduced, and commercial quality was deteriorated, so that the improvement in quality is not sufficient to compensate for the loss of yield. Generally, the negative effects of ozone exceeded the positive effects.
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