Physiological Responses to Drought ofLolium perenneL.: Measurement of, and Genetic Variation in, Water Potential, Solute Potential, Elasticity and Cell Hydration

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Abstract
Thomas, H. 1987. Physiological responses to drought of Lolium perenne L.: Measurement of, and genetic variation in, water potential, solute potential, elasticity and cell hydration.—J. exp. Bot. 38: 115–125. Clonally-replicated genotypes of Loiium perenne L. were grown in a controlled environment. Leaf water potential (ψw) osmotic potential (ψs), turgor potential (ψp = ψw – ψs), elasticity (E), leaf hydration (g water per g dry matter, H) and number of green leaves per tiller (NGL) were measured before and during a 42 d drought treatment. A simplified method of estimating E (at ψw < 1·0 MPa) using only six measurements was developed to permit a measurement rate of 8 leaves per hour. Measurement errors in all characters were 3% or less. During drought, ψw and ψs (at ψw = 0·5 MPa) decreased significantly, ψp and E increased significantly, and H decreased slightly. Plant size during drought was negatively correlated with ψs, and H and positively correlated with ψp, osmotic adjustment, E and NGL. Measurements made on the genotypes before draughting did not give a reliable indication of their physiological condition after adaptation to drought. Genetically controlled variation (‘broad sense heritability’) of drought-adapted plants for E was 15%, ψw 23%, ψs, 34%, ψp, 35%, H 34% and NGL 64%. The possibilities for, and effectiveness of, divergent selection of genotypes with high and low expression of the characters are discussed.