Cotton (Gossypium hirsutum L.) Alcala SJ‐2 was grown in an activated carbon‐filtered greenhouse and exposed to biweekly 6‐hour ozone fumigations at a concentration of 490 µg m−3. Two ozone treatments were used, differing in age at initial exposure and total ozone dose. Sacrificial harvests were taken from all treatments at 14‐day intervals to monitor plant response and to provide the basis for growth analysis techniques.Ozone reduced the vegetative growth and boll production in both ozone treatments. The dry weights of all partitioned plant parts were reduced with the largest reductions occurring in roots and bolls. Fumigated plants initially produced fewer leaves with significantly less leaf area. A period of stimulated leaf and branch production followed the initial growth depression. Boll production was depressed 48% in both ozone treatments. Mean relative growth rates of partitioned plant parts were extremely good predictors of absolute responses. Mean net assimilation rates of ozone‐stressed plants were reduced throughout growth. The ozone‐treated plants were characterized by larger mean leaf area ratios, which accounted for elevated plant mean relative growth rates at 64 days of age.

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A commercial variety of pole tomato (Lycopersicon esculentum Mill. H-11) was exposed to 20 and 35 parts per hundred million (pphm) ozone for 2.5 hours, 3 days each week over a period of weeks. Extensive foliar injury, defoliation, and highly significant reductions in plant biomass occurred at both exposure levels. However, fruit yield was significantly reduced only at the higher 35 pphm ozone concentration. This reduction was due to a decrease in the number of fruit and not to a decrease in fruit weight. Fruit yield in the 20 pphm treatment was equal to that of the control despite a 27% reduction in total dry weight of plants. These results indicate the presence of a threshold for the effect of ozone on yield.Additional Index Words: foliar injury, fruit, threshold.

A multiple regression analysis of yields of ‘6718 VF’ tomato (Lycopersicon esculentum Mill.) from 11 field plots along an ambient ozone gradient in southern California indicated that ozone was responsible for a significant reduction in fruit size. Ozone dose accounted for 85% of the reduction in fruit size and was at least 3.3 times more important than any of the monitored meteorological variables in predicting the percentage of marketable fruit. High ambient ozone depressed production and caused a significant decrease in fruit size over time. A model describing the reduction in marketing container yield (% reduction = 0 + (.0232 x dose)) predicted a 50% reduction at a dose of 2000 pphm-hours > 10 pphm.

Foliar ozone sensitivity evaluations of 5 fresh market tomato (Lycopersicon esculentum Mill.) cultivars from fumigation experiments were contrasted with field trial yields at Riverside, California, a high ambient dose location (3798 pphm-hour > 10 pphm). Foliar injury was not an accurate indicator of yield response as a correlation of foliar susceptibility and yield rankings was insignificant. Cultivar production characteristics at the South Coast Field Station (222 pphm-hour > 10 pphm) and at Riverside were identical with standardized field plots of ‘6718 VF’ from a concurrent experiment. Reduced fruit size and depressed early season production, previously correlated with ozone dose, were characteristic of all cultivars planted at Riverside. Comparisons of cultivar production rankings revealed that ‘H-ll’ and ‘6718 VF’ yielded significantly more, in terms of weight and number of fruit harvested than ‘Ace’, ‘Polepak’, or ‘Earlypak 7’. All cultivars except ‘Ace’ produced equivalent yields in terms of weight at South Coast Field Station.