Phänotypisierung von Raps- und anderen Brassica-Genotypen zur Identifizierung von Resistenzquellen gegenüber Sclerotinia sclerotiorum

Abstract

The aim of this work was the development of suitable screening methods for resistance evaluation of oilseed rape cultivars against S. sclerotiorum. With these methods, possible sources of resistance had to be identified. Three methods have been developed, which evaluate the characteristics of resistance on different bases. Beside field experiments, which are strongly depending on climatic conditions and are very time and cost intensive, a greenhouse screening and a laboratory assay, which determines the reaction of the tissue against the pathogenicity factor, oxalic acid, have been developed. First genotypes, which were provided by the involved breeders, have been screened with the mentioned methods for evaluating a broad range of differentiation. Thus the complete variability, which is available for the breeders, has been used. By combining the three different methods, it was possible to show a lack of variation in this material. Therefore it is not possible to use this material in further resistance breeding. Nevertheless the reproducibility of the greenhouse screening and the oxalic acid assay was shown by using material with a higher differentiation. This material consists out of wild Brassica species, which have shown different resistance reactions. In the available cultivars and the used resynthesized oilseed rape genotypes a mechanism seems to be existing, which reduces the penetration efficiency and thus also the disease incidence. In the wild Brassica species a quantitative physiological resistance can be found, which reduces the rate of spread in plant material. This until now unused mechanism seems to be a possibility to increase resistance in breeding material, assumed that the described screening methods are used. Despite this mechanism sources of resistance have been found in Chinese oilseed rape cultivars. These cultivars also decrease the rate of spread but have no effect on the infectionefficiancy. The use of these sources of resistance in field experiments, which are the third and maybe most important method in breeding for resistance, was not possible. On the one hand the resynthesized oilseed rape made out of the wild species was not available. On the other hand the Chinese cultivars show an insufficient winter hardiness.There were several similarities between cultivars in field experiment 2007/08, in which no material from the breeders has been used, and the UFOP (Union zur Förderung von Oel- und Proteinpflanzen e.V.) variety trials, which are conducted on several locations and in several years. Because of this it was possible to demonstrate the reliability and the significance of the field experiments. A prerequisite is therefore a sufficient disease level, which can not be guaranteed because of changing climatic conditions.Artificial inoculations of roots under greenhouse conditions at different temperatures besides the observation of spring infestation in the field, indicate infection of roots in the field in the beginning of the growing season. Wounds, caused by insects or frost, may play an important role in this kind of infection. Differences in reaction of the used cultivars were not very obvious in spring infestation.In further experiments a resistant cultivar as a standard for greenhouse screenings and oxalic acid assays should be created by transformation of the spring oilseed rape cultivar Drakkar. For this reason a gene coding for oxalate oxydase and a gene coding for oxalate decarboxylase was used. A successful transformation and expression of the inserted genes has been demonstrated. Nevertheless in none of the phenotyped transformation events an influence of the genes on the phenotype could be observed. Beside the reaction of this transgenic material on the pathogen itself in greenhouse experiments, an oxalic acid assay was conducted to observe the effect of oxalic acid itself. Because even in this assay there was no influence of the genes on the phenotype a missing or incorrect transcription, an insufficient activity of the enzymes or an insufficient amount of the enzyme in the tissue can be suggested. Over all it can be stated, that suitable screening methods for further breeding have been developed and possible sources of resistance have been identified. Thus tools are available for breeders to increase resistance of oilseed rape against S. sclerotiorum.