The magnitude of heterosis provides a basis for genetic diversity and guideline to the choice of desirable parents for developing superior F1 hybrids. This study was carried out to exploit hybrid vigour and for building gene pool to be exploitation in population improvement. Heterosis and nature of gene action for morphoagronomic traits, oil content and fatty acid composition in linseed. Eight parents, their 28 F1crosses and one check variety (Berene) were evaluated in a randomized complete block design with three replications in season 2022/23 at HoletaAgrcultural Research Center farm field. The analysis of variance revealed that the parents and hybrids included in the investigation exhibited significant differences between treatments for all the characters, indicating a considerable amount of variability among the genotypes. cross P1xP4 was the top ranked hybrid among three standard heterosis for early maturity that could adapt and escapefrom climatic and pest disasters. Three crosses with high mid parent, better parent and standard heterosis were P2xP5, P3xP8 and P5xP7 for its maximum primary branches, while cross P2xP5 was for capsules.For seed yield per plant, P1xP2 hadhigh standard heterosis with bestpromising performance. Two crosses (P3xP8 and P5xP8)also had highstandard heterosis for high linoleic acid. The selected crosses for each trait had high potential for recombination breeding to develop better pure lines. In short, all parents used in these crossescan be used for future breeding of linseed in Ethiopia.

Keywords: heterosis; mid-parent; better-parent; standard heterosis; linseed; Half diallel