| Clubroot of many crops caused by Plasmodiophora brassicae is an economically important disease on cruciferous vegetables and rape. Presently the use of resistant varieties is the most cost-effective control measure. Since the pathogen consists of various pathotypes and takes on a sophisticated genetic makeup, effective selection of resistant sources will be of great significance to the disease-resistant breeding. Based on the investigation of clubroot occurrence in affected areas, then inoculated with pathogen populations isolated from Zhijiang and Changyang, the resistance of95main cultivars of cruciferous vegetables were identified in this study. Meanwhile, the two representative cultivars with resistance or susceptibility to clubroot were chosen to make aborative microscopic observation and comparison on physical structures and histologic changes during the two infection stages of the pathogen after inoculation, hoping to reveal the nosogenesis of Plasmodiophora brassicae and resistance mechanism of the hosts. The main research results are as follows:1. Resistance of the cruciferous vegetable cultivars to clubroot:Among the95varieties tested with Changyang isolate,23resistant varieties were identified, of which7cultivars including CR fujiang, Eshulianghong NO.2, Hongshan Flowering stalk showed highly resistance. The other cultivars displayed susceptibilities of different levels, of which16varieties were highly susceptible. Of the91cultivars challenged by Zhijiang isolates,47varieties were resistant, including35varieties of highly resistance. And the others were susceptible cultivars.2. Resistance of the cruciferous vegetable cultivars to different isolates of Plasmodiophora brassicae:Of the91cultivars tested with both Changyang and Zhijiang isolate, appraisal results of36cultivars differed sharply, while it was identified as resistant with one isolate for a certain cultivar, the other isolate tested it as susceptible. Out of the10introduced cultivars,8resistant cultivars were identified, only2varieties resisted both the two isolates;45resistant varieties were identified in land races, of which15cultivars possess resistance to both isolates. 3. The relevance of variety resistance and pathogen development during root hair infection:Two varieties CR fujiang and Xinxuan zaoshu NO.5were selected as representatives of resistant and susceptible cultivars respectively, and were used in the research on infection histology. It demonstrated that the development of pathogen in root hairs of susceptible host is the same as that in resistant host basically. Pathogen development in both hosts experienced several stages such as adsorption of root hairs, the injection of zoospore cytoplasm, reproduction of plasmodium, the differentiation of zoosporangium, release and transfer of zoospores. The differences lied in that the root hair infection rate in susceptible host was significantly higher than that of resistant host, and pathogen developed quickly in susceptible host.4. The correlation of variety resistance and cytohistology changes during cortical infection:The observation on root histology alteration in resistant and susceptible hosts showed that cell nucleus had swollen and deformed in both hosts during cortical infection. The pathogen would damage the cell wall of the susceptible host and even break it in the end, some host cells would eventually turn into "giant cells" due to hormone imbalance. While cell wall of resistant host would suffer less serious destruction, with intercellular layer intact. In the later period, many nuclei were differentiated in plasmodium, distributed around host nucleus, but in resistant host this development would be impeded.The resistant cultivars and materials screened out in this study would be of considerable application value in the control of clubroot via resistant varieties and disease-resistant breeding. |
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