Water use efficiency, carbon isotope discrimination and biomass production of two sugar beet varieties under well-watered and dry conditions

Two sugar beet (Beta vulgaris sp.) varieties, which were supposed to differ in drought tolerance, were exposed to drought stress in a growth chamber and a container experiment in field. The aim was to test for (i) differences between the varieties in water use efficiency (WUE), biomass production and distribution and (ii) the relationship between WUE and carbon isotope discrimination (A), and between biomass production and A. Significant differences in WUE were detected between plants of well-watered and drought treatments in both experiments, but not between the varieties. Production losses due to drought were large for both varieties in both experiments. Losses in the growth chamber were up to 50 % of plant dry weight and the corresponding value in the field was 24 %, when plants were given 60 and 30 %, respectively, of the full-watered treatments. Significant negative correlations between WUE and A were found, but not between biomass production and A, when both varieties were included. Negative correlations between WUE and A were also found for each variety separately. The results suggest that A estimates from leaf tissue of sugar beet may provide a useful tool for genetic selection of drought-tolerant sugar beet varieties.