GROWTH AND WATER RELATIONS OF SIMULATED SWARDS OF LOLIUM-PERENNE L SELECTION LINES WITH CONTRASTING LEAF OSMOTIC POTENTIALS

Two selection lines of Lolium perenne, which had different leaf lamina osmotic potential (psi(S)) when droughted in controlled environments, were grown as vegetative simulated swards in containers of soil 1.0 x 1.3 x 0.9 m deep in the glasshouse. Water was withheld during July, August and September. Under irrigation the low-psi(S) line had leaf lamina and leaf base-psi(S) 0.06 MPa lower than the high-psi(S) line. Under drought, the two lines did not differ significantly in lamina-psi(S) but leaf base-psi(S) was 0.16 MPa lower in the low line than in the high line. Upon rewatering, most of the osmotic adjustment in the leaf bases was lost within 2 d, but that in the laminae was more stable. Herbage growth under irrigation was similar in the two lines until September, when it was greater in the high-psi(S) line. Drought reduced herbage growth, and also regrowth rates following rewatering, but the two lines did not differ in their sensitivity to drought. Selection for low-psi(S) also increased leaf extension rates, and reduced tillering and leaf water conductance of irrigated plants. The results are discussed in relation to selecting for improved drought resistance on the basis of physiological characters.