Winter sown lentil compared with spring sowing, will enhance yield, provide better rotational and soil conservation system and consequently increase lentil area and production in Iran. Cold susceptibility in winter sown lentil is one of the abiotic stresses which affect its production. Hence, in order to evaluate the cold hardiness of 39 lentil genotypes, obtained from the lentil germplasm collection of College of Agriculture Karaj, (Iran) and ICARDA (Syria), a randomized block design experiment with three replications was performed over the years 2000 and 2001 in Karaj conditions (NL 35o). The level of cold hardiness among the lentil genotypes were measured by examining the alive and dead seedlings after being exposed to natural winter and spring cold weather and expressed in percentage. The absolute minimum temperatures during the two growing seasons were -10oC and -9.8°c, respectively. Phenological traits (such as days to 50% flowering, seed filling period, maturity), seed yield and 1000 seed weight were recorded in each year. Pooled analysis of variance for genotypes response to winter sowing were statistically significant among various traits. The histogram for cold hardiness percentage showed that the tolerant lentil genotypes (91-95% winter hardiness) comprised only 4% frequency percentage and the tolerant genotypes (71-90% winter hardiness) was 28 percent. The coefficient of variation for winter hardiness among the genotypes were about 17.5%. This variation is due to environment since no genotypic heredity for cold hardiness in lentils has yet been reported. The lentil seed yield had a relatively higher variation (about 28.6%) compared to other traits. Nevertheless, the seed yield had a significant and positive correlation (r=%20**) with cold hardiness percentage, and the high yielding genotypes also showed very high or high cold hardiness percentage. Between cold hardiness percentage and duration from sowing to harvest, a quadratic relation (R2= %19) existed and very high and high tolerant genotypes had shorter duration to maturity. On the whole, the lentil genotypes in this study were grouped into four clusters based on cold hardiness percentage, seed yield and maturity traits. The high tolerant accessions 2, 36, 7, 13 and 32 along with relatively high tolerant accessions 16, 12 and 26 had the lowest euclidean distance and all were grouped in one cluster.
)