HETEROSIS AND MIXING EFFECTS IN WINTER OILSEED RAPE

Open-pollinated synthetics and lineal cultivar structures of rapeseed (Brassica napus L. var. napus) are used for commercial production. All are different in degree of heterozygosity and heterogeneity. This study was conducted to determine heterosis and mixing effects, and their interactions on yield and yield stability. From four randomly-chosen winter oilseed rape cultivars the F1, F2, two-component cultivar mixtures and Syn1 were produced using a diallel design. Furthermore, three two-component F1 mixtures were produced. The cultivars, cultivar mixtures, F1's and Syn1's were tested at four locations in northern Germany in 1982-1983 and 1983-1984. The F2's and F1 mixtures were tested in 1983-1984. Mixtures of cultivars outyielded cultivars by 6%. The F1's outyielded cultivars (by 15%), cultivar mixtures (by 8%), and Syn1 (by 6%). The F1 mixtures outyielded F1's in pure stands by 6%. The F2's surpassed cultivars by 4%, but yielded less than expected based on the parental and F1 results. The stability parameter ecovalence revealed a positive effect of increasing heterozygosity and heterogeneity on yield stability. The effect of heterogeneity on yield stability was greater than the effect of heterozygosity. The F1 mixtures showed high yield and high yield stability. The results suggest that heterogeneous hybrid structures of winter rape may be superior to homogeneous hybrid structures.