Increasing demand for vegetable oil and protein requires breeding efforts to enhance the yield of oilseed rape. This can be achieved by reducing seed cellulose, hemicellulose and lignin content. The objective of the study was to analyse seed yield and important agronomic traits of two distinct bulks of genotypes from two crosses, with low (6%) and high seed lignin content (10%). The two genotype bulks were formed by mixing seeds of 12 doubled haploid lines with either low or high lignin content.The genotypes were selected from two large doubled haploid populations based on lignin content, flowering time and plant height. The bulks were field-tested in replicated yield trials. Seed quality analysis confirmed significant differences in seed lignin content between the two bulks. Seed oil content was moderately higher in the low lignin bulks of both crosses. Seed, oil and protein yield in both crosses were moderately to significantly higher in the low lignin bulks. Further breeding for reduced fibre content will help increase seed oil and protein content.

For oilseed rape (Brassica napus L.), hybrid varieties of two growth types, semi‐dwarf and normal, are on the market. So far, the acceptance of semi‐dwarf hybrids is very limited, though they have several advantages such as higher N efficiency and drought tolerance. It is undecided whether both growth types are influenced in the same way by front‐border effects in plot yield trials. This study analyzed if semi‐dwarf hybrids were discriminated against in yield trials, due to differences in the exploitation of the front‐border area, since they could not lean and grow as far into the adjacent path due to a reduced height compared to normal type hybrids. From 2016–2018, eight pairs of near‐isogenic hybrids, bzh semi‐dwarf and normal type hybrids, were grown in three environments, with three replications and two treatments: Plants were harvested with and without the plot front‐border, and seed and straw yields were determined. Root electrical capacitance was also measured. Semi‐dwarf hybrids outperformed normal type hybrids in seed yield in the dry season of 2018, whereas the reverse happened in the more humid season of 2017. Across environments, semi‐dwarf hybrids had a higher positive front‐border effect (11.2%) than normal type hybrids (9.6%), leading to a relative overestimation of semi‐dwarf hybrid yields. There was no significant difference in root electrical capacitance between growth types across environments. It could be concluded that semi‐dwarf hybrids were not disadvantaged with regard to front‐border effects in plot trials, when compared to normal type hybrids. However, elimination of the plot front‐border area might improve comparisons between semi‐dwarf and normal type cultivars.

Oilseed rape is a major oil crop and a valuable protein source for animal and human nutrition. Lignin is a non-digestible, major component of the seed coat with negative effect on sensory quality, bioavailability and usage of oilseed rape's protein. Hence, seed lignin reduction is of economic and nutritional importance. In this study, the major QTL for reduced lignin content found on chromosome C05 in the DH population SGDH14 x Express 617 was further examined. SGDH14 had lower seed lignin content than Express 617. Harvested seeds from a F2 population of the same cross were additionally field tested and used for seed quality analysis. The F2 population showed a bimodal distribution for seed lignin content. F2 plants with low lignin content had thinner seed coats compared to high lignin lines. Both groups showed a dark seed colour with a slightly lighter colour in the low lignin group indicating that a low lignin content is not necessarily associated with yellow seed colour. Mapping of genomic long-reads from SGDH14 against the Express 617 genome assembly revealed a homoeologous non-reciprocal translocation (HNRT) in the confidence interval of the major QTL for lignin content. A homologous A05 region is duplicated and replaced the C05 region in SGDH14. As consequence several genes located in the C05 region were lost in SGDH14. Thus, a HNRT was identified in the major QTL region for reduced lignin content in the low lignin line SGDH14. The most promising candidate gene related to lignin biosynthesis on C05,PAL4, was deleted.

Key message A homoeologous non-reciprocal translocation was identified in the major QTL for seed lignin content in the low lignin line SGDH14. The lignin biosynthetic gene PAL4 was deleted. Abstract Oilseed rape is a major oil crop and a valuable protein source for animal and human nutrition. Lignin is a non-digestible, major component of the seed coat with negative effect on sensory quality, bioavailability and usage of oilseed rape’s protein. Hence, seed lignin reduction is of economic and nutritional importance. In this study, the major QTL for reduced lignin content found on chromosome C05 in the DH population SGDH14 x Express 617 was further examined. SGDH14 had lower seed lignin content than Express 617. Harvested seeds from a F2 population of the same cross were additionally field tested and used for seed quality analysis. The F2 population showed a bimodal distribution for seed lignin content. F2 plants with low lignin content had thinner seed coats compared to high lignin lines. Both groups showed a dark seed colour with a slightly lighter colour in the low lignin group indicating that a low lignin content is not necessarily associated with yellow seed colour. Mapping of genomic long-reads from SGDH14 against the Express 617 genome assembly revealed a homoeologous non-reciprocal translocation (HNRT) in the confidence interval of the major QTL for lignin content. A homologous A05 region is duplicated and replaced the C05 region in SGDH14. As consequence several genes located in the C05 region were lost in SGDH14. Thus, a HNRT was identified in the major QTL region for reduced lignin content in the low lignin line SGDH14. The most promising candidate gene related to lignin biosynthesis on C05, PAL4, was deleted.