Root and shoot characteristics related to drought tolerance were studied for Prunus persica, P. andersonii, P. besseyi, P. maritima, P. subcordata, and P. tomentosa. In general, shoot characteristics were more closely associated with drought adaptation than root characteristics across species. The most xeric species, andersonii, had the most xerophytic leaf morphology, highest rates of leaf gas exchange, high root length/leaf area and root weight/leaf area ratios, but had root length and hydraulic conductivity similar to that of more mesic species. Water use efficiency (WUE) increased as water potentials (ψ) dropped to -3.0 to -4.0 Mpa during a 5-7 day drought for the xeric andersonii and subcordata. However, after an initial increase, WUE decreased with declining ψ in the other 4 species, indicating that carboxylation was affected by stress in the -1.5 to -3.0 range of ψ for besseyi, maritima, persica and tomentosa. CO2 assimilation (A) decreased linearly with ψ during drought in all species, but the ψ at which A reached zero was not well correlated with drought adaptation. Root hydraulic conductivity was similar for all species, indicating a lack of importance of this parameter for drought tolerance. The data suggest that introduction of xerophytic shoot characteristics into commercial cultivars of Prunus would improve drought tolerance to a greater extent than using drought tolerant species as rootstocks.
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