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Sowing date is the most important factor affecting yield and it''s components of rapeseed. Suitable sowing dates make the environmental conditions favorable for plant during the days of seedling emergence and its establishment. This experiment was conducted in split plot layout with randomized complete block design with four replications at Seed and Plant Improvement Institute (SPII) during 2000–2002 years. Main plots were sowing date with four levels of: Sept. 11، Sept. 21، Oct. first and Oct. 11. Sub-plots were rapeseed varieties including SLM046، Zarfam، Colvert and Orient. The traits evaluated were: Plant height، number of branches، number of pods per plant، number of seeds per pod، 1000 seeds weight، seed yield، oil contain and oil yield. Combined analysis of variance showed that sowing date had significant effect on seed yield، oil yield، number of pods per plant، number of branches and 1000 seeds weight (p<0. 01). The highest yield (3295 and 2877 kg/ha) was in the first planting time (Sept. 11) and the second planting time (Sept. 21)، respectively. Variety effect was highly significant only for number of seeds per pod and 1000 seed weight. The highest number of seeds per pod was related to SLM046 and Orient varieties (24. 3 and 24. 2، respectively). Interaction between sowing date and variety was significant only for number of branches and number of seeds per pod (p<0. 05). The results of this experiment show that the most suitable sowing date at Karaj is from 11th to twenty-one of September and decrease in seed yield occurs due to significant decrease in yield components، when planting time is delayed.

Seed samples of three oil-seed rape cultivars SLMO46, Orient and Zarfam (Regent×Cobra) with 35, 25 and 15% moisture contents were provided from seed production fields. Cortrolled deterioration test was conducted in laboratory by maintaining seeds at 40, 45 and 50°C for durations of 12, 24 and 48 hours. Analysis of data on different seed quality assessment parameters showed that except coefficient of velocity of germination, other traits were affected by deterioration treatments. Seeds of cultivar Orient had the lowest viability, seedling vigour and other related traits at 50°C for 48 hours treatment. The dioriorated seed were sown in field and some characteristics such as seedling emergence speed, field emergence index, seedling height, seedling fresh and dry weight and seedling vigour index were assessed. Analysis of data showed that only seedling fresh weight and seedling vigour index were not affected by the effect of year. Interaction effects of cultivar, temperature and duration of seed deterioration were significant for all measured characters. Seeds of Orient cultivar deteriorated at 50°C for 48 hours had the lowest field emergence speed and field emergence index. Study of correlation between different traits assessed in laboratory and field indicated that except seedling fresh weight, other field traits correlated to the final germination percent and other laboratory traits. The results of the present study revealed that application of controlled deterioration test has the potential to evaluate seed quality and seedling emergence and establishment of oil-seed cultivars in field