Heterosis and Combining Ability Estimates in F2 Flax Populations as Influenced by Plant Density1

Abstract

Seed yield, its three components (bolls per unit area, seed size, and seeds per boll), oil content, and iodine value were studied in F2 populations of a diallel cross among nine cultivars of flax (Linum usitatissimum L.) at two locations and three plant densities.Average heterosis for yield in F2 was 6% relative to the midparent values. Four F2 populations exceeded in yield the high‐yielding parent by 15 to 19%. One F2 population, ‘Russian’ ✕ C.I. 1664, exceeded by 5.5% the yield of ‘Marine’, the highest yielding cultivar. Varying plant density did not affect the magnitude of heterosis, mean oil percentage, iodine value, nor the estimates of combining ability. Plant density did have a significant effect on mean yields and on the yield components, and showed a significant interaction with genotypes for yield and bolls per unit area. In spite of the latter interaction, seven of the 36 F2 populations were among the highest 25% in yield in all three densities. The interactions of locations with genotypes were significant for most characters, which suggests that more than one test location should be used to evaluate hybrid flax populations. General combining ability effects were significant and much larger for all characters than were specific combining ability effects at all densities.