effects of planting dates on yield and yield components of fall rape oilseed cultivars

proper sowing date along with providing normal growth rate in rape oilseed plants significantly leads to higher seed and oil yield via decreasing cold damages. the experiment was conducted as factorial with two factors including sowing dates with 4 levels (12 and 23 september, 2 and 12 october) and genotypes with 5 levels (modena, licord, okapi, opera and zarfam) in three replications. the study was carried out in east azarbaijan research center for agriculture and natural resources (46? and 2? e, 37? and 58? n) during 2007-2008. the results indicated that genotypes at late sowing date had significantly lower leaves and rosette diameter, because at that time average air temperature was below rape oilseed base temperature (5 ?c) and indicated higher cold damage. plants in the first and the second planting dates in compare with two late planting dates, indicated significantly higher values of plant height, pods per plant, seed and oil yields. late planting was accompanied by decreasing pods per plant and seed yield reduction in plants. it seems that 12- 23 september could be suitable period to cultivate fall genotypes of rape oilseed in khosrov shahr and areas with similar climate (cold and semi-arid, according to koppen climatic classification). among studied genotypes, modena and licord had lower amounts of leaves per plant and rosette diameter. also opera had the longest pod length. finally genotypes indicated similar seed and oil yields and therefore could be suitable for cultivation in khosrov shahr and areas with similar climate. it seems that induced effects of environmental factors such as drought periods and increasing temperature, could affect growth rate via primary differences (such as leave numbers) amonge genotypes. it is possible to investigate these traits by repeating the experiment.