Influence of the Semi-dwarf Growth Type on Seed Yield and Agronomic Parameters at Low and High Nitrogen Fertilization in Winter Oilseed Rape

In cereals like wheat (Triticum aestivum L.) or rice (Oryza sativa L.), a short-straw ideotype is characteristic for all modern cultivars, mainly due to the use of genes affecting the dwarf genotype. In oilseed rape (Brassica napus L.), several dwarf mutants are known but so far not widely used. An interesting approach is the production of semi-dwarf hybrids from dwarf and normal-type parents, which might have an increased harvest index (HI) and a higher grain yield, especially when nitrogen (N) availability is restricted. To this point, no systematic comparison using a large number of semi-dwarf and normal-type hybrids has been published. A double haploid (DH) population was developed that was segregating for the bzh dwarf locus with 54 dwarf and 54 normal-type lines. By crossing with a normal-type tester, 108 testcrosses were produced with 54 hybrids each of semi-dwarf and normal types. These were evaluated under high and zero N fertilization in five and seven environments, respectively, for yield and agronomic parameters. Quantitative trait loci (QTL) were estimated for yield-relevant traits. Semi-dwarf hybrids had a significantly higher yield compared with normal types in N-deficient conditions (2.24 and 2.05 Mg ha(-1)). At an optimal N supply, no significant difference between growth types was found for seed yield. Oil content was slightly lower in semi-dwarfs under both N treatments, whereas this was compensated by oil yield. All major QTL for plant height, straw yield, HI, and seed yield co-segregated with the bzh dwarf locus on linkage group A06, indicating that the dwarf gene is not only reducing plant height but also causing increased HI and higher yield under N limitation for semi-dwarf hybrids. We conclude that semi-dwarf hybrids are of high interest for the N-balanced oilseed rape production, especially when N is scarce.