This study carried out in order to investigate the effects of salinity on carbon isotope discrimination (∆) of shoots and roots of four sugar beet cultivars (cv) including Madison (British origin) and three Iranian culivars (7233-P12, 7233-P21 and 7233-P29). Plants were grown in sand culture medium in greenhouse conditions. Sugar beet cultivars irrigated with saline water (tap water as control, 50 mM, 150 mM, 250 mM and 350 mM of NaCl and CaCl2 in 5 to 1 molar ratio) from 4 leaves stage for 16 weeks. Carbon isotope discrimination significantly decreased with increasing salinity. Significant differences of ∆ between shoot and root were observed in all cvs and all levels of salinity. Madison cv showed lower ∆ in shoot and root than other three cvs at all levels of salinity expect control, but cv 7233-P29 had significantly higher ∆ values at saline conditions of 150 mM and above. Although the regression of ∆ and Ci/Ca is positive, the slope of regression line is different from predicted by theory, indicating an underestimation of ∆ in these samples. Relatively more 13C (lower ∆) was found in root as compared with shoots. Therefore, ∆ might be applicable, as a useful tool, for study of salinity tolerance of sugar beet genotypes.

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