ABSTRACT
Commercial production of Pima cotton has recently begun in California's San Joaquin Valley. Early field observations indicate early cutout and leaf senescence symptoms, in parts of the Valley that resemble ozone damage. Ozone sensitivity of Pima has not been investigated. Therefore we imposed a range of ozone treatments on well-watered Pima and Acala varieties currently grown in the San Joaquin Valley, using field exposure chambers. The Pima cotton (cv. S-6), recently introduced from Arizona, was found to be more sensitive to ozone than the Acala line (Si-2), selected in the San Joaquin Valley. Leaf senescence, gas exchange behavior, yield and yield components, and fiber quality were all more affected in Pima than in Acala. Yield of Pima was reduced to nearly zero under ozone conditions that have been observed in this production area. Recent economic successes with Pima in California may be associated with the low levels of air pollution prevailing in the last few years. Current efforts to select Pima varieties under San Joaquin Valley conditions of moderate ozone pressure may prove to be critical to long-term Pima production in California.
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