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Pressure-Volume Characteristics of Genotypes of Three Wheatgrass Species¹

A need exists for drought tolerant forages that can produce acceptable yields on limited water. Techniques to accurately predict performance under drought stress are essential for selection of drought tolerant forages. Objectives of this study were to measure water relations of important forage species using the pressure volume (P-V) method and to evaluate its usefulness predicting drought tolerance. The study was conducted using clonal selections of crested wheatgrass [Agropyron desertorum (Fisch.) Schult.], western wheatgrass (A. smithii Rydb.), and intermediate wheatgrass [A. intermedium (Link) Haloc.]. Pressure-volume measurements were made using a pressure chamber on plants grown in both field and glasshouse environments. Data from the P-V curves for initial turgor loss point, osmotic potential at full hydration and leaf water potential at zero pressure potential indicated differences among genotypes for all three species of wheatgrasses. Although only a limited number of genotypes were evaluated results appear more promising for selecting genotypes for drought tolerance in western than in crested or intermediate wheatgrasses. Species comparisons based on data from the P-V relationship shows that genotypes of crested and western exhibit water relations that coincide with their greater drought tolerance. The P-V technique requires a high labor input and will require modifications for practically evaluating large breeding populations for drought tolerance.

Key Words: Pressure chamber • Pressure potential • Osmotic potential • Leaf water potential • Desiccation tolerance • Range grasses • Water-use-efficiency

² Plant physiologist and research geneticists, respectively, USDA-ARS, Northern Great Plains Res. Lab., P. O. Box 459, Mandan, ND 58554.

Received for publication October 8, 1982.