SCREENING ALMOND CULTIVARS FOR OZONE SUSCEPTIBILITY

Abstract

Uniform nursery stock of five almond cultivars (Prunus dulcis Mill., cv Nonpareil, Mission, Carmel, Butte, and Sonora) propagated on peach (P. domestica L. Batsch.) rootstock were planted in open-top fumigation chambers on 19 April 1989 at the University of California's Kearney Ag Center located in the San Joaquin Valley of California. The trees were exposed to three atmospheric ozone partial pressures (charcoal filtered air, ambient air, or ambient air+ozone) from 1 June to 2 November 1989. The mean 12-h (0800-2000 h) ozone partial pressure measured in the open-top chambers during the experimental period averaged 0.038, 0.060, and 0.112 μPa Pa-1 ozone in the charcoal filtered, ambient, and ambient+ ozone treatments, respectively. Leaf net CO2 assimilation and cross-sectional area growth of Nonpareil trees were reduced by increasing atmospheric ozone partial pressures, but Mission trees were unaffected. Foliage of Nonpareil almond abscised prematurely in the ambient and ambient+ozone treatments. The susceptibility of the Butte, Carmel, and Sonora almond cultivars to ozone was intermediate between the Nonpareil and Mission cultivars.