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Effect of freezing damage at seedling stage in different sugar beet cultivars

l his srudy was conducted to determine freezing damages on sugar beer seedling (at cotyledon. two and tour leaves srages) in seven sugar beet cultivars (Shirin, Rasol. Gadook, 276, 428, 7233 and BRI) in Karai m ~002 cropping season ln first experiment, sugar beet seedlings at the four mentioned ~!a~e~ were transferred to the growth chamber and exposed [0 zero. -2 and 4°(ʹ lor two periods of 4 and 8 bours Second experiment. was carried out in the field to compare the results of greenhouse and field. Leaf samples were taken at Three growth stages of sugar bed seedlings. transferred to growth chambers. and exposed to freezing temperatures, Assessment of freezing damages was performed using visual (survived or dead) and leaf chlorophyll florescence measurements. The results showed that freezing damage was 0,5. 8 and 85%, for 10\\ temperatures of zero. -2, and -rc. respectively. Freezing damage on the detached leaves from field and the seedlings grown in growth chamber showed similar results, Chlorophyll fluorescence measurements as index tor freezing damage showed that all increase of freezing stress caused a decrease ill the amount of ["I (maximum chlorophyll fluorescence) and Fv/Ftn (photochemical efficiency of phorosystem II). Sugar beet cultivars were more susceptible at lWllleaves stage as compared tL1 four- leaves stage. The threshold of freezing damage had no significant differences among sugar beet cultivars, however. BRI and Gadook cultivars showed the lowest and highest susceptibility to freezing, u-spcctivcly. Results also showed that threshold of freeling damage on sugar beet seedling in concerned culuvars \\ʹ<1:::ʹ ~2GC and the lower the temperature [he more damages occur in the field.