Browsing by Subject "Downy mildew"

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Epidemiologische Aspekte der Falschen Mehltauinfektion durch Plasmopara viticola an Vitis
(2007) Keil, Sven; Spring, Otmar
The obligate biotrophic oomycete Plasmopara viticola (Berk. & Curt.) Berl. & de Toni causes downy mildew on grapevine. Plasmopara viticola is one of the economically most important pathogens in viticulture, with severe losses in yield of up to 70%. Existing prognosis models for plant protection in viticulture only allow yes/no statements on possible infection events in the vineyard. On the basis of these models, the severity of infections remain uncertain, although this represents a crucial point for an efficient application of fungicides. At low infestation severity, the application of protective fungicides at the end of the incubation period usually is sufficient. The low level of infestation can be tolerated and only further propagation of the pathogen must be prevented. In contrast, at high infestation severity curative fungicides have to be applied as soon as possible, because otherwise too much host tissue would be destroyed. Based on epidemiological studies and field experiments a prognostic concept has been designed, which enables the user to evaluate the relevance of infection events of grapevine downy mildew. This work has been carried out in the context of the research project ?Optimierung der Peronospora-Bekämpfung im Rebschutz auf der Basis eines erweiterten Prognosemodells (Forschungsvorhaben des Bundesministeriums für Ernährung, Landwirtschaft und Verbraucherschutz Nr. 514-33.54/01HS048)?. The developed concept was then integrated into the existing prognosis model and should support both consultants and winegrowers in using plant protection agents only in case of an expected increase of infestation frequency and severity. In this way, an effective and more economical use of fungicides is possible, which contributes to economic savings and reduces pesticide contamination of the environment. In the present study, aspects of sporangiogenesis, infestation of host tissue and hibernation, spreading of sporangia, interaction between vine leaves and sporangia as well as the climatic conditions during infection were analysed and evaluated with respect to the impact on epidemiology. The results improve existing literature data and deliver new insight to the epidemiology and biology of Plasmopara viticola.
Genetic variation for tolerance to the downy mildew pathogen Peronospora variabilis in genetic resources of quinoa (Chenopodium quinoa)
(2021) Colque-Little, Carla; Abondano, Miguel Correa; Lund, Ole Søgaard; Amby, Daniel Buchvaldt; Piepho, Hans-Peter; Andreasen, Christian; Schmöckel, Sandra; Schmid, Karl
Background: Quinoa (Chenopodium quinoa Willd.) is an ancient grain crop that is tolerant to abiotic stress and has favorable nutritional properties. Downy mildew is the main disease of quinoa and is caused by infections of the biotrophic oomycete Peronospora variabilis Gaüm. Since the disease causes major yield losses, identifying sources of downy mildew tolerance in genetic resources and understanding its genetic basis are important goals in quinoa breeding. Results: We infected 132 South American genotypes, three Danish cultivars and the weedy relative C. album with a single isolate of P. variabilis under greenhouse conditions and observed a large variation in disease traits like severity of infection, which ranged from 5 to 83%. Linear mixed models revealed a significant effect of genotypes on disease traits with high heritabilities (0.72 to 0.81). Factors like altitude at site of origin or seed saponin content did not correlate with mildew tolerance, but stomatal width was weakly correlated with severity of infection. Despite the strong genotypic effects on mildew tolerance, genome-wide association mapping with 88 genotypes failed to identify significant marker-trait associations indicating a polygenic architecture of mildew tolerance. Conclusions: The strong genetic effects on mildew tolerance allow to identify genetic resources, which are valuable sources of resistance in future quinoa breeding.
Peronospora aquilegiicola made its way to Germany: The start of a new pandemic?
(2020) Thines, Marco; Buaya, Anthony; Ali, Tahir; Brand, Thomas
Peronospora aquilegiicola is a destructive pathogen of columbines and has wiped out most Aquilegia cultivars in several private and public gardens throughout Britain. The pathogen, which is native to East Asia was noticed in England and Wales in 2013 and quickly spread through the country, probably by infested plants or seeds. To our knowledge, the pathogen has so far not been reported from other parts of Europe. Here, we report the emergence of the pathogen in the northwest of Germany, based on morphological and phylogenetic evidence. As the pathogen was found in a garden in which no new columbines had been planted recently, we assume that the pathogen has already spread from its original point of introduction in Germany. This calls for an increased attention to the further spread of the pathogen and the eradication of infection spots to avoid the spread to naturally occurring columbines in Germany and to prevent another downy mildew from becoming a global threat, like Peronospora belbahrii and Plasmopara destructor, the downy mildews of basil and balsamines, respectively.
Plasmopara viticola, the downy mildew of grapevine : phenotypic and molecular characterization of single sporangium strains infecting hosts with different resistance levels
(2015) Gómez Zeledón, José Javier; Spring, Otmar
The downy mildew of grapevine, Plasmopara viticola, is one of the most important pathogens in viticulture. Its genetic diversity had been assessed in some previous studies using molecular markers, but the diversity of the infection behavior has not yet been addressed adequately. Therefore, the development of a fast, reliable and uncomplicated assay to screen for pathogen phenotypes on host with different resistance levels was a major task of this work. A leaf disc test was proposed, evaluating sporulation and necrosis produced by the pathogen on Vitis plants with different susceptibility. Using this bioassay, interesting strains were assessed and kept for future studies. The urgent need to work with genetic homogeneous inoculum was shown, because the assays revealed a high phenotypic diversity in isolates collected from the field as a bulk sample. Hence, a cloning technique to obtain single sporangium strains was found useful to avoid working with mixed genotypes. The leaf disc bioassay also allowed screening for fungicide resistance in P. viticola populations. Isolates resistant to dimethomorph and metalaxyl, two important fungicides for oomycetes control, were detected. Higher resistance was associated with fields were the fungicide application was high as well. Some strains were even resistant to doses where the fungicide exhibits phytotoxic activity to grapevine. The approach of characterizing P. viticola pathotypes on different host plants of Vitis vinifera cultivars and Vitis species from North America and Asia revealed a broad spectrum of fully susceptible to completely resistant reactions. This information is of direct practical value in future plant breeding programs, but also provides the chance to select specific host-pathogen combinations to study the mechanisms of resistance or susceptibility. Fluorescence microscopy revealed how the infection progress of highly and lowly virulent strains advance in tolerant and susceptible hosts, and which points of the infection are interesting for future studies. On the molecular level, effectors were investigated to trace their possible involvement in the infection process. It was found that RXLR 1, NLP 1, Elicitin like 2, Glucanase inhibitor 2 and 4 , and 1,3-ß Glucanase 2 are candidates which are upregulated in the earliest infection stages. Following the here established methodology and suggested strategy it should be possible in the future to get a better insight in the mechanisms of infection and resistance of grapevine downy mildew.
Untersuchungen zum asexuellen Gentransfer bei biotrophen Oomyceten anhand der Fallbeispiele Plasmopara halstedii und Peronospora tabacina
(2009) Hammer, Timo; Spring, Otmar
Evidence for gene transfer during the asexual life cycle of certain biotrophic oomycetes was searched for in this study in order to evaluate the potential impact of such parasexual recombination on the variability of these important plant pathogens. Therefore, two case studies with Plasmopara halstedii, the causal agent of sunflower downy mildew, and with the tobacco blue mould pathogen, Peronospora tabacina, were conducted. Although the life cycles of both pathogens lack the possibility of genetic recombination, the organisms differ significantly in their variability. Using molecular methods, several indications for interspecific parasexual recombination between the near relatives Plasmopara halstedii and Plasmopara angustiterminalis were found, giving a possible explanation for the unexpected variability of these pathogens. Asexually formed offspring from dual infection experiments with the two Plasmopara species showed pheno- and genotypic parental traits in new combination and could be cultivated under double selective pressure. The recombinant strain ?R? was studied over 30 generations. Up to the 9th generation and after single sporangium infection, nuclear and mitochondrial traits of both parents were detected in ?R?, indicating a heterokaryon with nuclei and mitochondria of both parental strains. Starting with the 10th generation only fungicide-resistance remained as Pl. halstedii-specific trait, whereas all other detected signals were Pl. angustiterminalis-specific, which indicated true genetic recombination. As one possible mechanism for the genetic exchange it was shown that nuclei can be exchanged between neighboured hyphae via anastomoses and that more than one nucleus can be distributed into one developing sporangium. To prove anastomoses between the different Plasmopara species, specific optical labelling of the participating hyphae is a prerequisit. However, only transient expression of an optical marker gene was achieved, yet. Additional experiments for establishing a stable transformation system were conducted, but were not yet successful in selecting transgenic strains. In contrast to the study on Plasmopara, there was no evidence for recombination in Peronospora tabacina. Neither anastomoses nor heterokaryotic sporangia were found throughout the study. The results are concordant with the findings that tobacco blue mould shows very low variability and that only two phenotypes are known so far from studies in Europe. As the two types of the pathogen, which differ in fungicide sensitivity, did not interact during parallel infection of the same host tissue, they were characterized in detail. Several new pheno- and genotypic differences could be revealed, showing the genetic distance between the two types of the pathogen. A simple PCR detection system to differentiate the two genotypes was created and more than 50 European isolates of tobacco blue mould were monitored.