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Charakterisierung von resistenz-überwindenden Isolaten des Beet necrotic yellow vein virus (BNYVV) in Zuckerrüben und Stabilität der Resistenz in Abhängigkeit von Umweltbedingungen

dc.contributor.advisorVarrelmann, Mark Prof.
dc.contributor.authorBornemann, Kathrinde
dc.titleCharakterisierung von resistenz-überwindenden Isolaten des Beet necrotic yellow vein virus (BNYVV) in Zuckerrüben und Stabilität der Resistenz in Abhängigkeit von Umweltbedingungende
dc.title.translatedCharacterization of resistance-breaking isolates of Beet necrotic yellow vein virus (BNYVV) in sugarbeets and resistance durability in terms of environmental conditionsde
dc.contributor.refereeVarrelmann, Mark Prof.
dc.description.abstractengBeet necrotic yellow vein virus (BNYVV) is the causal agent of rhizomania (root madness) in sugar beet and is spread to all sugar beet growing areas worldwide. The virus is transmitted by the soil-borne plasmodiophoromycete Polymyxa betae to the lateral roots of sugar beet plants. Typical symptoms of the disease are severe root proliferation, discoloration of the vascular tissue and leaves showing an upright position. An infection can cause high yield and sugar losses. Control of the disease is mainly possible by using sugar beet genotypes carrying a single dominant resistance gene called Rz1. In resistant plants, the virus replication in lateral roots is reduced and spread to the taproot is inhibited. Due to minor differences in the coat protein sequence on the RNA2 the virus can be divided into four types (A, B, P and J). The 25kDa protein P25 encoded by the RNA3 was identified as a viral pathogenicity factor. In recent years, aggressive strains of the virus occured which, besides the common symptoms, expressed high virus titers in lateral roots of resistant sugar beet genotypes. This caused high yield losses and puts the disease back into focus. An increased selection pressure and an augmented occurrence of point mutations probably led to a high variability at the amino acid positions aa67-70 of the viral pathogenicity factor. Thus, specific amino acid changes are responsible for an increased aggressiveness of the virus. It is still unclear whether the vector P. betae influences the occurrence of resistance-breaking strains. In a greenhouse trial, different resistance-breaking strains were loaded into a natural P. betae population in a virus-free field soil. Subsequently, resistance-breaking properties were compared in a resistance test. The results showed that the vector has no influence on resistance-breaking properties of BNYVV strains. In consequence of global warming, it can be expected that the conditions for an infection by the vector will improve via rising soil temperatures and increasing precipitation. In order to analyze the occurrence of resistance-breaking BNYVV strains related to global warming in Germany, a container trial was set up under field conditions. Therefore, a B type-infested field soil from Bavaria was used. The soil in the containers was heated up by a heating mat. The temperature was adjusted variably compared to the unheated reference soil. In five rotations, susceptible and Rz1-resistant sugar beet genotypes were tested under the same trial conditions but at different soil temperatures compared to the reference soil. No elevated virus titers in lateral roots of Rz1-resistant plants were detected. The results suggest that a slight increase of the soil temperature does not lead to an occurrence of resistance-breaking strains in Germany. All resistance-breaking A type strains known so far possess a valine at the first position of the hyper-variable amino acid tetrad aa67-70 of the viral pathogenicity factor P25. An A type with a different tetrad composition was identified in Rz1-resistant sugar beet genotypes on several fields in England, the Netherlands, and Germany showing typical rhizomania symptoms. This strain possessed resistance-breaking properties in a resistance test under standardized greenhouse conditions and after loading into a virus-free P. betae population. In field trails in the Netherlands and Germany typical symptoms were observed. Rz1-resistant sugar beet plants had higher virus titers compared to susceptible plants when resistance-breaking BNYVV strains were loaded into a P. betae population. These strains are subject to a fitness penalty and show a selective disadvantage. To verify this observation experimentally, competition experiments in the greenhouse were set up. By means of “deep sequencing” it was shown that resistance-breaking strains out-compete non-resistance-breaking A and B type strains in Rz1-resistant plants. The influence of other (soil-borne) pathogens remains unexplained. The effect of the sugar beet genotype on the occurrence of resistance-breaking strains should be considered in the future, especially by the
dc.contributor.coRefereeBecker, Heiko C. Prof.
dc.contributor.thirdRefereeMärländer, Bernward Prof.
dc.subject.gerViröse Wurzelbärtigkeitde
dc.subject.engresistance durabilityde
dc.subject.engclimate changede
dc.affiliation.instituteFakultät für Agrarwissenschaftende
dc.subject.gokfullLand- und Forstwirtschaft (PPN621302791)de

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