evaluation of sugar beet (beta vulgaris l.) to freezing tolerance under controlled conditions

to evaluate the freezing tolerance in sugar beet (beta vulgaris l.), seven cultivars (suprema, jolge, monotunno, giada, pp8, sbsi1, palma) were exposed to the 10 temperatures (0, -2, -4, -6, -8, -10, -12, -14, -16 and -18˚c) .the study carried out as a factorial arrangement of treatments based on randomized completely design with three replications at college of agriculture, ferdowsi university of mashhad in 2009. plants were kept until 4-5 leaf stage in natural environment at early autumn, then transferred to the thermogradient freezer. no. of leaf, leaf area, leaf dry weight, survival percentage, lethal temperature 50 according to the survival percentage (lt50su) and reduced dry matter temperature 50 (rdmt50) were determined after 21 days (end of recovery duration). results showed that by reduction of temperature no. of leaf, leaf area and its dry weight significantly decreased. amounts of lt50su between the cultivars were significantly different. monotunno with lt50su -16.9˚c was more cold hardly than others and pp8 and sbsi1 with lt50su -15.2˚c were susceptible to the freezing temperatures. decreasing temperature below -14˚c reduced survival percentage in all cultivars. pp8 and sbsi1 cultivars perished completely at -16˚c while others like suprema and monotunno had high survival percentage, but all of them killed at -18˚c.correlation between rdmt50 and lt50su was high but not significant. however there was a strong and significant correlation (r = 0.99**) between lt50su and survival percentage.