INJURY AND YIELD RESPONSES OF SPINACH CULTIVARS TO CHRONIC DOSES OF OZONE IN OPEN-TOP FIELD CHAMBERS

Spinach (Spinacia oleracea L.) cultivars were exposed continuously during growth to carbon-filtered air or nonfiltered ambient air in open-top field chambers. Constant low concentrations of ozone (O3) were added to the varying ambient concentrations in the nonfiltered-air chambers for 7 hr (0920 to 1620 EDT) per day. There were significant differences in the amount of foliar injury and shoot growth decrease among 11 spinach cultivars exposed for 7 hr/day to 0.13 ppm of O3; America, Winter Bloomsdale, and Seven-R were less sensitive to foliar injury than Chesapeake, Hybrid-612, and Dixie Market. Shoot growth of America and Viroflay was affected less and Hybrid-612 and Dark Green Bloomsdale more than that of most other cultivars. The cultivars America, Winter Bloomsdale, Hybrid 7, and Viroflay were exposed for 38 days to determine threshold doses of O3 for injury and yield effects. The threshold 7 hr/day mean O3 concentration for foliar injury was between 0.02 and 0.06 ppm. The threshold for a significant decrease in shoot growth of most spinach cultivars was between 0.06 and 0.10 ppm. Shoot fresh weights of plants grown in the ground at 0.06, 0.10, and 0.13 ppm were 18, 37 and 69% less, respectively, than plants grown at 0.02 ppm. Comparative values for potted plants grown in a 1:1:1 mixture of sand/soil/Pro-Mix BX were 4, 25, and 65%, respectively.; Spinach cultivars were exposed continuously during growth to carbon-filtered air or nonfiltered ambient air in open-top field chambers. Constant low concentrations of ozone (O//3) were added to the varying ambient concentrations in the nonfiltered-air chambers for 7 hours per day. There were significant differences in the amount of foliar injury and shoot growth decrease among 11 spinach cultivars exposed for 7 hours/day to 0. 13 ppm of O//3; America, Winter Bloomsdale, and Seven-R were less sensitive to foliar injury than Chesapeake, Hybrid-612, and Dixie Market. Shoot growth of American and Viroflay was affected less and hybrid-612 and Dark Green Bloomsdale more than that of most other cultivars. The cultivars America, Winter Bloomsdale, Hybrid 7, and Viroflay were exposed for 38 days to determine threshold does of O//3 for injury and yield effects. The threshold for a significant decrease in shoot growth of most spinach cultivars was between 0. 06 and 0. 10 ppm.