ISHS Acta Horticulturae 630: XXVI International Horticultural Congress: Nursery Crops; Development, Evaluation, Production and Use
IMPROVING DROUGHT TOLERANCE OF TREES: THEORETICAL AND PRACTICAL CONSIDERATIONS |
| Author: | B.M. Cregg |
| Keywords: | Carbon isotope discrimination, water-use-efficiency, genetic variation, tree selection, physiological genetics |
| Abstract:
Selecting trees for improved drought tolerance has long been of interest for those involved in landscape horticulture and urban forestry. However, there are several pitfalls that need to be addressed in designing studies for selecting drought tolerant trees. Standardizing and quantifying the amount of drought to which trees are subjected is a major problem both in field studies and in pot studies. In field studies, variation in rainfall can limit the ability to apply a known amount of drought stress. In container studies, different growth rates among the genotypes can result in different levels of drought stress even at comparable levels of irrigation. In this paper, I discuss some of the theoretical and practical limitations of various drought-screening methods, and provide suggestions for methods that be may used to effectively identify trees with superior drought tolerance. I present examples of two techniques that have been effective in identifying variation in drought tolerance in seedling trees; stress-bed drought screening and the target water potential concept. Both of these techniques may be useful for screening a relatively large number of genotypes for drought tolerance. A second major constraint for screening trees for drought tolerance is determining the appropriate response variables to measure. Researchers have had varying degrees of success using single point-in-time measurements such as osmotic potential or gas exchange in identifying drought adapted genotypes. I present examples of the application of carbon isotope discrimination as an integrated measure of water use efficiency in studying genotypes of Pinus sylvestris, P. ponderosa and other conifers. I also discuss theoretical and practical limitations of using carbon isotope discrimination and other methods to identify drought-adapted genotypes. | |
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