Genetische und agronomische Charakterisierung von Raps-Mutanten mit gesteigertem Ölsäuregehalt

Abstract

The main breeding objectives of rapeseed (Brassica napus L.) have always been to increase yield, yield components, disease and pest resistance and more recently the seed quality too. The last mentioned goal means to take influence on the fatty acid profil and to produce an oil high in monounsaturated fatty acids (oleic acid) and low in polyunsaturated fatty acids (linoleic acid, linolenic acid). Rapeseed oils with a high concentration of oleic acid (breeding goal more than 80 %) are characterized by a reduced susceptibility to oxidative processes and a rise in temperature resistance and therefore of great importance for nutritional and industrial purposes. A breeding program to change the fatty acid composition in rapeseed was started in 1991 at the university of Göttingen. Seeds of B. napus, variety Wotan, had been exposed to the chemical mutagen EMS (Ethylmethansulfonat) and after sowing plant-mutants showing increased values of oleic acid could be identified. Unfortunately, the agronomical traits of these plants didn t come up to the expectations. In the study presented here these experiments are continued in order to get mutants that are high in oleic acid and simultaneously high in agronomical traits. Moreover, the newly found mutants should be characterized (DNA sequencing) and the specific location of their genes estimated. Rapeseeds of EMS-treated plants were cultivated and in the harvested seeds the contents of oleic acid measured. Some mutants of this M2-generation showed a significantly increased concentration in oleic acid. They were selected for field experiments between the years 2002 and 2007. During this period of time and cultivation in two different places 6 mutants proved to be stable with regard to their increased oleic acid values. Evaluation of the agronomical traits in 2006 and 2007 and a comparison with Wotan and the above mentioned elder mutants demonstrated that the yields of the new mutants were significantly higher than the elder mutants, respectively almost as high as Wotan. In the starting project of the mutagenesis program two mutated loci (HO1 and HO2) could be identified. HO1 locus is mainly seedspecifically expressed and equivalent to FAD2, the microsomal oleic acid desaturase. In order to find out whether the newly discovered mutants are also mutated in the same locus crossbreeding experiments between the old mutant 19661 and the new mutants were carried out. In case the mutation regarding the trait oleic acid content took place in different locations the splitting effect in M2-generation should lead to a separation. The results turned out to be convincing. In four crossings a clear splitting in the F2-generation could be recognized and that seems a likely supposition that the mutations responsible for increased oleic acid contents are located in two different loci. This assumption could be supported by genetic analysis. A further goal of the crossing experiments was it to compare the oleic acid contents between the descendant plants and the generation of parents. In all investigated cases we couldn t find any genotype among the descendants containing a higher amount of oleic acid than the parent generation. Investigation of the material with the aid of this technique confirmed the supposition that the increase of the oleic acid contents in our newly created mutants Mu12 and Mu13 results from an EMS-induced mutation in FAD2-I (A-region). In Mu12 at position 638 cytosine is substituted by thymine and in Mu13 this exchange took place at position 476. As a result of these mutations the oleic acid desaturase is modified by a replacement of the amino acid proline with leucine leading to an influence on the biosynthesis of oleic acid. Taken together the results presented here it can be established that new mutants of Brassica napus with increased oleic acid contents could be created and characterized. In comparison to already known HO-mutants possess the newly created ones significantly better agronomical traits and should be therefore of some interest for plant breeders.