Browsing by Subject "Pseudomonas syringae"

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    Neu auftretende bakterielle Blattfleckenerreger an Radies und Entwicklung eines Resistenztests als Grundlage für die Züchtung resistenter Sorten
    (2014) Scholze, Inka S.; Vögele, Ralf
    Radish is one of the most important vegetable crops in Rhineland Palatinate. During the last decades, an increase in bacterial leaf spots on radish has been observed. Although the bulb is unaffected, leaf spot symptoms lead to a decline in sales and profits as German consumers prefer marketable red radish bunches including the freshness-indicating foliage. So far, preventive methods for the control of bacterial pathogens on radish were limited to irrigation strategies (for example drip irrigation) or field hygiene. These methods are, however, often difficult to implement and their effect predominantly insufficient. Resistant or tolerant breeds would provide a solution, however, breeding companies have been lacking the necessary information regarding the causative agents and their biology and epidemiology needed for the development of such breeds. Previous examinations of infested plants and seed lots suggest different pseudomonads and Xanthomonas campestris as possible agents. The main objective of this study was therefore to identify the relevant pathogens causing leaf-spot symptoms on radish. Furthermore, another objective was to clarify the infection and growth requirements of bacterial pathogens on hosts for the development of a screening method for resistance to leaf spot pathogens on radish. On account of increasing compensation claims from breeding companies by farmers, the role of seed transmissibility was also to be determined. during a three year observation, bacterial pathogens from plants and seed lots were isolated and characterized. The characterization of unknown bacterial strains was performed by a combination of physiological and molecular methods. Molecular characterization methods such as 16s rDNA sequence analysis and MLST (multilocus sequence typing) were needed to complete the designation of P. syringae pathovars. In addition, virulence assays clarified the importance of single pathovars. Hence bacterial leaf spot pathogens could be determined as P. syringae pv. maculicola, P. viridiflava, P. cannabina pv. alisalensis and X. campestris whereas the former two species were the most abundant in Rhineland Palatinate. Infection trials on radish plants concluded that the different pathogens induced different typical symptom characteristics. To evaluate the influence of environmental factors such as humidity and temperature, it was demonstrated that inoculations with pseudomonads and a leaf spot inducing X. campestris strain caused successful infection and symptom development under a wide temperature range. Humidity was shown to be the most influential factor limiting infestation intensity with P. viridiflava displaying a higher demand for humid conditions than P. syringae pv. maculicola and X. campestris. All three types induced a higher disease infestation on radish plants in high humidity conditions (~94% rH) contrary to a lower infestation in dry conditions (~63% rH). In a first test series, plants inoculated with P. viridiflava were almost symptom free under dry conditions, whereas P. syringae and X. campestris were still able to induce leaf spots. Based on the results of infections assays, it was possible to develop a screening method on radish plants for resistance to the leaf spot inducing bacterial pathogen P. syringae pv. maculicola. The screening method was based on the spray-inoculation of radish leaves fixed in water filled orchid tubes, incubated under high humidity in a climate chamber at 24 °C day/10 °C night. Determination of resistance was performed 7 to 10 days past inoculation by rating disease intensity of infested leaves. Whereas tests could be performed by inoculations with P. viridiflava and P. cannabina as well as P. syringae, the latter proved to be most suitable for the screening method.