Kurtz, Andreas: Endophytic Fusarium oxysporum: Phylogeny and induced defense responses in banana plants against Radopholus similis. - Bonn, 2010. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5N-22491
@phdthesis{handle:20.500.11811/4221,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5N-22491,
author = {{Andreas Kurtz}},
title = {Endophytic Fusarium oxysporum: Phylogeny and induced defense responses in banana plants against Radopholus similis},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2010,
month = sep,

note = {The burrowing nematode Radopholus similis is a destructive pest of banana causing severe yield losses in plantations worldwide. R. similis infestation of the banana root is significantly reduced, when the root system is colonized by specific non-pathogenic Fusarium oxysporum endophytes. This enhanced resistance towards the nematode acts in a systemic manner. Until now, it is not clear how and why only specific isolates of this species of Fusarium induce what is called systemic induced resistance (SIR). In order to obtain a better understanding of this unique interrelationship, mutualistic F. oxysporum endophytes were phylogenetically compared both to each other and to the pathogenic forms of F. oxysporum f.sp. cubense. Molecular and biochemical aspects of SIR responses in the banana cultivar ‘Valery’ (AAA) were assessed.
RAPD, RFLP and sequence analysis of different DNA sequences were evaluated for their potential to infer the phylogeny of F. oxysporum isolates, which were characterized as being mutualistic by conferring enhanced resistance against R. similis. Most isolates originated from Uganda, Africa. Sequence analysis of the partial IGS region was identified as the best approach for inferring the phylogenetic relations of the Fusarium isolates to each other. It could be shown that non-pathogenic were clearly distinct from the pathogenic isolates and that isolates generally clustered according to their geographical origin by forming an independent African clade. However, in contrast to the scattered and genetic diverse mutualists and commensalists from Uganda, pathogens were arranged in an exclusive cluster showing only little genetic diversity. Therefore, pathogenicity can be considered a monophyletic trait, whereas mutualism must be considered polyphyletic.
NPR1 and PR-1 homologs of Musa AAA were chosen as marker genes for ISR and SAR respectively. Real-time PCR was used to monitor their expression in the leaves and roots of the banana cultivar ‘Valery’ (AAA) in response to treatments with chemicals, R. similis and mutualistic, commensalistic or pathogenic F. oxysporum isolates. Expression studies showed that, SAR and not ISR, was elicited by certain chemical inducers. The presence of R. similis alone did not lead to SAR or ISR. Nematode penetration was significantly reduced by the mutualistic Fo162 and the pathogenic Fo001, by 39% and 45%, respectively. PR-1 transcripts accumulated in response to the pathogen Fo001, suggesting the onset of SAR as part of the incompatible interaction between Fo001 and the Fusarium wilt resistant cultivar Valery. The accumulation of NPR1 and PR-1 transcripts did not increase in the presence of the mutualist Fo162, thus indicating that both ISR and SAR were not involved during SIR.
Root exudates extracts of Valery, colonized by Fo162, were collected on a XAD-4 matrix, extracted and both analyzed by RP-HPLC and tested in vitro biotest systems for their chemotactical activity towards R. similis. The RP-HPLC analysis of the root exudate extracts identified the identical set of 26 compounds for both treatments. Significant differences in compound accumulation were observed between the treatments. Nevertheless, the individual root exudate extracts did not show any repellent or attractant activity towards R. similis in an in vitro biotest system.
ISR and SAR seem to be irrelevant in the enhanced resistance against R. similis that is induced by mutualistic F. oxysporum isolates. Neither gene expression studies nor root exudate profiling indicated the actual mechanism that accounts for the enhanced resistance of banana against R. similis. However, the findings of the phylogenetic as well as the gene expression studies, along with routine VCG tests, support the safe use of mutualistic Fo162 as a R. similis management tool in banana production in future.},

url = {http://hdl.handle.net/20.500.11811/4221}
}

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