Growth Form and Yield Responses of Four Cotton Cultivars to Ozone
Cultivars of crop plants can differ widely in their susceptibilities to yield losses induced by the air pollutant ozone (O3), but relatively little is known of the physiological mechanisms that account for these differences. Cotton (Gossypium hirsutum L.) cultivars differ in degree of determinance, which may affect cultivar responses to O3 through effects on rates of maturation of the cultivars. Four cultivars of cotton grown in the field on a Hanford coarse sandy loam (coarseloamy, mixed, nonacid, Thermic Xerorthents) were exposed to three levels of O3 in open-top chambers to determine their relative susceptibility to O3, and to relate differences in susceptibility to morphological and physiological characteristics of the cultivars. Susceptibility to O3,-induced yield losses in these cultivars was directly correlated with degree of determinance so that cultivar rank in order of both increasing determinance and susceptibility to O3 was: SJ-2 < C1 < GC510 < SS2086. Differences among the cultivars in susceptibility to O3, were not associated with differences in rates of stomatal conductance. Instead, determinate cultivars appeared to be more susceptible to O3 because periods of peak flowering and boll set coincided with periods of high O3 concentration. Also, indeterminate cultivars appeared to have greater flexibility in altering branching patterns in response to O3,-induced leaf abscission than did determinate lines. Since most high-yielding, shortseason cotton cultivars have a determinate growth habit, these results suggest that production from short-season cotton cultivars may be limited by the prevalence of O3 air pollution in many cottongrowing regions of the USA.
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