Half F2 diallel crosses of six spring cultivars of rapeseed (Brassicanapus L.) were used to estimate heterosis effects of yield components, seed yield, oil percentage, and oil yield under limited nitrogen condition. Significant mean squares of general and specific combining abilities (GCA and SCA) were detected for pods per main axis, pods per plant, length of pod, seeds per pods, 1000-seed weight, seed yield, and oil content and oil yield indicated respectively the importance of additive and non-additive genetic effects for these traits. High narrowsense heritability estimates for 1000-seed weight, oil percentage, and oil yield indicating the prime importance of additive genetic effects for these traits. Most of the cross combinations with significant positive heterobeltiosis for seed yield had also significant heterobeltiosis effects for pods per plant and pods on main axis; therefore these traits can be used as indirect selection criteria for improving seed yield. Significant positive correlation of mean performances with heterosis and heterobeltiosis effects for most of the traits except 1000-seed weight indicated that selection of the superior crosses based on heterosis and heterobeltiosis effects will be effective for their mean performances improving these traits except 1000- seed weight. Significant positive correlation was determined between pods per plant and seed yield, indicating that this trait can be used as good selection criterion for seed yield improvement. The crosses including RAS-3/99 × RW-008911 and RAS- 3/99 × RGS-003 with high significant positive heterobeltiosis effects of seed yield were superior combinations for seed yield increasing.
