Effect of Salinity on Carbon Isotope Discrimination of Shoot and Root of Four Sugar Beet (Beta vulgaris L.) Cultivars

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A factorial pot experiment based on randomized complete blocks design with fourreplications was carried out in order to evaluate salt tolerance of four sugar beet cultivarsincluding Madison (British origin) and three Iranian cultivars (7233-P12, 7233-P21 and7233-P29) using carbon isotope discrimination (Δ). Plants were grown in sand culturemedium 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 withincreasing salinity. Significant differences of Δ between shoot and root were observed inall cultivars and all levels of salinity. Madison cv. showed lower Δ in shoot and root thanthe other three cultivars at all levels of salinity except the control, but cv. 7233-P29 hadsignificantly higher Δ values at saline conditions of 150 mM and above. Although theregression of Δ and Ci/Ca was positive, the slope of regression line was different from thepattern predicted by theory, indicating an underestimation of Δ in these samples.Relatively higher 13C (lower Δ) was found in root as compared with shoots.