Genetic Analysis of Seed Yield and some Agronomic Traits in Rapeseed Genotypes Under Normal and Late Sowing Conditions

In the persend study، 120 genotypes of rapeseed including ten lines، ten testers and their one hundred progenies were grown in normal sowing dates (first half of October) and late sowing date (first half of November) in two separate alpha-lattice designs with two replications in Karaj in 2010-11. The analysis of variance in each environment and the combined analysis of variance over the environments revealed significant differences among adjusted treatments in terms of yield and related traits in both normal and late sowing conditions. Therefore، there were high genetic diversity among genotypes for all traits. Line×tester analysis indicated a higher proportion of non-additive gene effects for yield and related traits in both conditions. Broad sense heritability was high for all traits under both normal and late sowing conditions (from 63. 14 to 89. 12%) which indicates the importance of genetic variation than environmental variance. However، narrow sense heritability was moderate for number of branches per plant، seed yield، plant height and number of siliques per plant (from 43. 42 to 56. 02 %) and low for number of seeds per silique and 1000-seed weight in both sowing conditions (36. 33 and 24. 61%)، respectively. Therefore، selection for seed yield and its components، especially the number of seeds per silique and 1000-seed weight in early generations would not be very effective. Both additive and non-additive gene action involved in the genetic control of all characters، but the role of non-additive gene action for number of branches per plant and seed yield (only late sowing)، plant height، number of siliques per plant، number of seeds per silique and 1000-seed weight (in each experimental conditions) was more evident. Estimation of combining ability of traits showed that testers T9، T2 and line T1 were the best general combiner for increasing seed yield. Hybrids T7×L1، T8×L5، T3×L8 and T8×L9 under normal sowing date and T3×L1، T9×L2 and T7×L3 under late sowing date conditions were the best specific combiner to increase seed yield. Some of hybrids also had the highest positive and significant heterosis for seed yield.