02395naa a2200193 a 450000100080000000500110000800800410001910000150006024501100007526000090018550000200019452016820021470000160189670000140191270000220192670000210194870000170196977302150198614689672006-03-03       2005    bl ---       0--  u    #d1 aTOBITA, S.  aWater use efficiency and carbon isotope discrimination in Brazilian soybean cultivars under water stress.  c2005  aResumo: P 5.85.  aWater use efficiency (WUE), or transpiration efficiency, is well known to closely relate with dry matter production under drought stress in many plants and crops. It can be applicable as a varietal screening criterion for drought tolerance, but the direct measurement of WUE in: field is not possible. In C3 plants, the relationship of WUE and carbon isotope discrimination (CID) has been empiricalIy documented and physiologicalIy elucidated. A pot experiment was conducted in Tsukuba, Japan, in summer of 2004, with precise and regular measurement of the amount of supplied and transpiring water for the estimation of WUE of soybean (Glycine max L. [Merr.]) cultivars from Brazil under well-watered and water-stressed conditions, as welI as instantaneous WUE (WUEi) in several occasions. Leaf samples were colIected of the youngest fulIy expanded trifoliate and analyzed for Ôl3C values by an IRMS, which were then converted to CID with use of -8.00% as the ÔI3C of the air. Under well-watered condition, WUE was ranged from 2.7 to 3.3 g L-1 and significantly higher in Conquista (drought-tolerant), as compared with BRS-183 (tolerant), BRS-185 and Aurora. WUE was apparently increased to be around 3.4 g L-1 in alI cultivars by water stress from the beginning of flowering for 25 days. of welI-watered Conquista leaves was significantly lower (17.7%) than other cultivars (around 19%). Under the water stress,  decreased to be from 17.2 to 17.9% for alI cultivars. There was a negative linear correlation (r2 = 0.929) between WUE and  so that it would be reasonable to estimate WUE in field-grown soybeans with the measurement of  for its application to drought screening.1 aNASTASA, V.1 aSENOO, S.1 aNEPOMUCENO, A. L.1 aFARIAS, J. R. B.1 aNEUMAIER, N.  tIn: INTERNATIONAL CONFERENCE ON INTEGRATED APPROACHES TO SUSTAIN AND IMPROVE PLANT PRODUCTION UNDER DROUGHT STRESS, 2., 2005, Rome. InterDrought - II: final program and abstract book. Rome, 2005. Não paginado.