evaluation of freezing tolerance in safflower (carthamus tinctorius l.) genotypes under controlled conditions

in order to evaluate the effect of freezing stress on safflower (carthamus tinctorius l.) genotypes, an experiment was conducted in faculty of agriculture, ferdowsi university of mashhad, iran. treatments included 6 genotypes (k.w.3, k.w.6, k.w.16, zarghan 279, line 295 and il-111) and freezing temperatures (0, -4, -8, -12, -16 and -20 ˚c). the trial was arranged as factorial based on completely randomized design with three replications. plants were grown in small pots in natural environment till 5-7 leaf stage and then transferred to controlled conditions and freezing stress were imposed. survival percentage, plant height, number of nodes per stem, length of internodes, leaf number and area, stem, leaf and plant dry weight were determined after three weeks (end of recovery). results indicated that there was no difference between genotypes in survival percentage and lethal temperature 50 (lt50) was between -13 to -13.5˚c. recovery of plants showed that the dry matter of safflower genotypes was significantly different and the lowest was belonging to il-111 genotype. the lowest lt50 and reduced dry matter temperature 50 (rdmt50) was belong to the line 295 and il-111 showing the recovery weakness of these two genotypes compared to others.