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Variation for Water-Use Efficiency in Alfalfa Germplasm

L. L. Tieszen

USDA-ARS Plant Germplasm Research and Testing Unit, Washington State University, Pullman, WA 99164-6402, and Augustana College, Sioux Falls, SD 57197

^* Corresponding author.

Carbon isotope discrimination () shows promise for estimating water-use efficiency (WUE, grams dry weight/gram water transpired) in C₃ crop species. The objective of this study was to determine if variation for is present in diverse alfalfa (Medicago sativa L.) germplasm, and if is correlated with direct measurements of WUE. Eighteen alfalfa accessions originating from 13 countries were established in 1990 in irrigated and dryland environments at Central Ferry, WA, in a fine-silty, mixed, mesic Typic Natrixeroll soil. Significant differences among accessions for leaf were observed with no significant environment x accession interaction. Based on 1990 results, high (PI 420400, 20.3%0), middle (P1 522242, 19.7%0), and low (PI 434600,18.9%o) accessions were selected for additional field evaluation in 1991. For the dryland environment in 1991, leaf of PI 434600 was lower than PI 420400, but accession differences were not observed in the irrigated environment. In greenhouse pot studies, accessions did not differ for total plant WUE. But shoot WUE values all differed significantly, and were 2.43,2.09, and 1.73 g dry wt./kg transpiration for the low, middle and high accessions, respectively. Total plant WUE was correlated with only under drought stress (r = –0.55**, n = 30), but shoot WUE and were correlated within well watered (r = –0.63**, n = 30) and drought-stressed (r = –0.73**, n = 30) treatments. Correlations between shoot WUE and root:shoot values were negative and significant at P = 0.01, suggesting that root/shoot carbon partitioning influenced shoot WUE. Results show reproducible variation for in alfalfa germplasm, and that is potentially useful for evaluating alfalfa germplasm for WUE.

Received for publication April 9, 1993.

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