A factorial pot experiment based on randomized complete blocks design with four replications was carried out in order to evaluate salt tolerance of four sugar beet cultivars including Madison (British origin) and three Iranian cultivars (7233-P12, 7233-P21 and 7233-P29) using carbon isotope discrimination (
). Plants were grown in sand culture medium in greenhouse conditions. Sugar beet cultivars were irrigated with saline water (tap water as control, 50, 150, 250 and 350 mM of NaCl and CaCl2 in 5: 1 molar ratio) from 4-leaf stage for 16 weeks. Carbon isotope discrimination significantly decreased with increasing salinity. Significant differences of
between shoot and root were observed in all cultivars and all levels of salinity. Madison cv. showed lower
in shoot and root than the other three cultivars at all levels of salinity except the control, but cv. 7233-P29 had significantly higher
values at saline conditions of 150 mM and above. Although the regression of
and Ci/Ca was positive, the slope of regression line was different from the pattern predicted by theory, indicating an underestimation of
in these samples. Relatively higher 13C (lower
) was found in root as compared with shoots.

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