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Clubroot, caused by Plasmodiophora brassicae infection, is a disease of growing importance in cruciferous crops, including oilseed rape (Brassica napus). The affected plants exhibit prominent galling of the roots that impairs their capacity for water and nutrient uptake, which leads to growth retardation, wilting, premature ripening, or death. Due to the scarcity of effective means of protection against the pathogen, breeding of resistant varieties remains a crucial component of disease control measures. The key aspect of the breeding process is the identification of genetic factors associated with variable response to the pathogen exposure. Although numerous clubroot resistance loci have been described in Brassica crops, continuous updates on the sources of resistance are necessary. Many of the resistance genes are pathotype-specific, moreover, resistance breakdowns have been reported. In this study, we characterize the clubroot resistance locus in the winter oilseed rape cultivar “Tosca.” In a series of greenhouse experiments, we evaluate the disease severity of P. brassicae-challenged “Tosca”-derived population of doubled haploids, which we genotype with Brassica 60 K array and a selection of SSR/SCAR markers. We then construct a genetic map and narrow down the resistance locus to the 0.4 cM fragment on the A03 chromosome, corresponding to the region previously described as Crr3. Using Oxford Nanopore long-read genome resequencing and RNA-seq we review the composition of the locus and describe a duplication of TIR-NBS-LRR gene. Further, we explore the transcriptomic differences of the local genes between the clubroot resistant and susceptible, inoculated and control DH lines. We conclude that the duplicated TNL gene is a promising candidate for the resistance factor. This study provides valuable resources for clubroot resistance breeding programs and lays a foundation for further functional studies on clubroot resistance.

The plants have developed several defense mechanisms to counteract pathogens. Among others, it includes activation of antioxidant enzymes like β-glucosidase and guaiacol peroxidase (GPX). These proteins participate in the oxidation of phenolic compounds, contributing to their increased fungitoxicity. The study aimed to analyze changes in the activity of β-glucosidase and GPX in four genotypes of winter oilseed rape (Mendel, Monolit, Polka, line L1425) inoculated with seven isolates: Alternaria brassicicola, Alternaria brassicae, Alternaria alternata (3 strains), Ulocladium chartarum (syn. A. chartarum), and Cladosporium cladosporioides. We noted that the varieties of oilseed rape, tested fungal species, and time of the plant material collection had significant (P < 0.001) effect on the activity of β-glucosidase and GPX per protein and fresh matter content comparing to the control group. A. brassicicola caused the highest mean increase in β-glucosidase and GPX activity in all examined genotypes, while other pathogens had a lower impact. Significantly lower β-glucosidase activity inoculated by various pathogens was noted between the L 1425 line and other varieties. GPX activity was in the opposite, the lowest activity was recorded in the Mendel variety, and the highest in the L 1425 line. Keywords Oilseed rape • β-glucosidase • Guaiacol peroxidase • Alternaria black spot Communicated by M. Horbowicz.

The aim of the study was to determine the rate of colonization of oilseed rape by selected species causing black spot of oilseed rape in order to determine their mutual influence on the development and intensity of the infection. Isolates of Alternaria alternata, Alternaria tenuissima, Alternaria brassicicola, Ulocladium chartarum and Cladosporium cladosporioides were used in the study. The plants were inoculated with spores of the listed species at various combinations. The intensity of the infection was evaluated 5, 10 and 15 days after inoculation and the plant material was collected for mycological analysis. The most severe disease symptoms were caused by A. brassicicola, mainly in combination with A. tenuissima and U. chartarum. The symptoms of alternaria black spot of crucifers were also caused by U. chartarum and A. tenuissima species, which are not recognized as pathogens of oilseed rape. A. alternata infection caused weak disease symptoms. These results were confirmed by the mycological analyses.

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