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English

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http://hdl.handle.net/10251/168651

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Where these data come from
Cross resistance of Brassica spp. against vascular pathogens, Fusarium oxysporum f.sp. conglutians, Verticillium longisporum and Xanthomonas campestris pv. campestris

Abstract

Fusarium oxysporum f. sp. conglutinans (FOC) is an important fungus of the soil that causes vascular wilt disease in Brassica spp. crops, resulting in severe losses in both yield and quality. However, crop rotation and the application of fungicides are not effective in managing this disease due to the difficulty of eradicating this pathogen from the soil. Breeding of resistant cultivars is therefore essential for disease control. So far, a variety of Japanese cabbage (cv.) Anju (Brassica oleracea), containing an Anju allele that is found in a single dominant resistant FOC-Bo1 gene, has shown improved resistance to FOC, while rapeseed resistance (B.napus, OSR) is not yet available. As OSR is a natural interspecific hybrid between B. oleracea and B. rapa, different forms of rapeseed were crossed with the Anju cabbage CV. to generate the resintered OSR. Parental lines and resynthesised lines were used in this study. Due to similarity in colonisation, two other vascular pathogens Verticillium longisporum (VL) and Xanthomonas campestris pv. campestris (XCC) were used to assess cross-resistance of tested plant material. To improve the evaluation systems, several inoculation methods and a molecular detection system were also evaluated. To shape the assessment methods, greenhouse experiments were carried out, testing 4 isolates of 3 pathogens in two reference OSR plants with contrasting resistance responses. For FOC treatment, root immersion with conidium suspensions and soil inoculation with chlamydosporas was applied. Although no significant variations were found in the severity of the disease (DS) and stable correlations between the different inoculation methods and spores concentrations in FOC treated assays, root immersion with 105 cfu/ml conidium suspension showed an obvious contrasting symptom in the reference plants. Compared to soil inoculation with microsclerotia of LTV, plants inoculated by root immersion with 106 cfu/ml of conidium suspension showed a faster development of the symptoms of the disease, which was as rapid as the development of the disease in inoculated plants with 105 cfu/ml of OC conidium suspension. Plants inoculated by immersion of roots with 108 cfu/ml of XCC showed a clear symptom of the disease and have a disease development rate similar to that of FOC and LV, while the lowest concentration and other inoculation methods (inoculation with cotyledons and foliar spraying of bacterial suspension) were not successful. The selected inoculation methods were applied to analyse the susceptibility of parental lines and lines resintered to FOC, VL and XCC. The increased severity of the disease and the reduction in the effects of delayed growth indicated that the resintered OSR resulting from the crossing with the Anju variety is more resistant to FOC. In addition, a significant reduction in susceptibility to XCC on the RS line was found, indicating that Anju allele has a cross-effect that increases resistance to XCC. However, no effect of Anju allele on VL resistance was found. To verify the visual observation, a molecular detection system was also set up to assess the resistance of OSR. 16 pairs of primers were evaluated for the detection of FOC, VL and XCC derived from the literature or from the design itself using real-time PCR. Primers with high sensitivity and specificity were selected to quantify fungal DNA.

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