Breeding for a reduced glucosinolate content in the green mass of rapeseed to improve its suitability for biogas production

Abstract

Brassica napus L., a plant that belongs to the Brassicaceae family is one of the main oil crops. Inside its seeds glucosinolates appear to be the main secondary glycoside, sugar containing component with sulfur containing bindings. Plant breeders have tried to lower the glucosinolate levels of seeds of rapeseed so that the high-protein seed meal remaining after oil extraction can be used as animal food. Products such as the nitriles and isothiocyanates are toxic components. Some of the glucosinolate types or alkenyles have negative effects in animal nutrition such as progoitrin. Very little is known about the function and roles of glucosinolates in the vegetative tissue of flowering winter rapeseed. The decomposition products are possibly inhibiting for bacteria in fermentation processes, caused by the very reactive side chains, released after cleavage with the myrosinase enzyme. The main objectives were to explore and define the genetic basis of the synthesis of glucosinolates in the green matter of oilseed rape and their effect on biogas production, to investigate the genetic variation of the glucosinolate contents and pattern in the vegetative tissue in classical breeding material and resynthesized rapeseed lines, to acquire information that determines the influence of the glucosinolate content and pattern in the green matter on the biogas production and finally to develop and characterize a quantitative trait loci map based on a mapping population from a cross. Causes of genetic variation are diverse, from so called mutations towards differences in chromosome number, whether this genetic variation is potentially available for certain secondary components such as the glucosinolates. More recently developed varieties with low glucosinolate levels in seeds but high glucosinolate levels in leaves are more resistant to pests and still provide a protein-rich seed residue for animal feeding. Winter rapeseed resynthesized parents and testcrosses with high biomass yielding lines were tested under different environments. Besides this a double haploid population from a cross between an exotic line (Gaoyou) and a cultivar were grown and analyzed for their glucosinolate content. These alternative crosses are made to find out more about differences in essential acting key genes that reveal the sequences behind exotic lines competing and interfering with local breeding forms. The glucosinolate content within the leaves does not correlate with the seed glucosinolates; also there is no correlation between methane, leaf and stem glucosinolates. Attention is focused on the leaf glucosinolates to identify those quantitative trait loci, which are situated in the genome and which are responsible for the glucosinolate content within the leaves. The determination of genetic variation of leaf, stem and seed glucosinolates in resynthesized winter rapeseed lines is a rather exceptional step in plant genomics. Although this study does not go into detail in the molecular level, a small jumping-leap is taken when the location of the traits is estimated. Further genetic studies are necessary to develop appropriate breeding strategies to reduce or increase leaf, stem and seed glucosinolates in winter rapeseed lines. Segregating populations of winter rapeseed lines should be tested in the future for their glucosinolate content in the leaves, stems and seeds. The polymorphisms for the occurrence of leaf stem and seed glucosinolates might be explained by their phenotypical differences, but also by the different functioning of these specific plant parts. Whether the number of genes involved in leaf glucosinolates is different from those involved in the functioning of the seed glucosinolates is not known. The higher the genetic variation for the resulting winter rapeseed breeding lines however, the better their persistence in different environments, where for example insect resistance is required.