Browsing by Author "Coelho, P. S."
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- Downy mildew evaluation in wild rocket genotypes (Diplotaxis tenuifolia (L.) DC) under field and controlled conditionsPublication . Coelho, P. S.; Pereira, A. L.; Reis, João; Carranca, C.; Lopes, V. R.; Leitão, JoséWild rocket downy mildew (DM) is a foliar disease caused by the oomycete Hyaloperonospora spp. that limits the production of brassicas, especially in temperate climates, infecting plants at all growth stages. During 2021 autumn season, a field trial (polytunnel) with a set of 40 wild rocket accessions from different origins (harvest missions, gene banks, commercial cultivars) was installed in a commercial enterprise located in Odemira, southern Portugal. The plants were naturally infected by Hyaloperonospora spp. and were visually evaluated 71 days after sowing. Field observations of adult plants evidenced differences among accessions concerning the DM resistance and agronomic traits (e.g., flowering date, vigour, plant habit, leaf serration). Sixteen wild rocket accessions were identified with an interesting resistance response to DM in adult phase. In a previous study, the wild rocket accessions were tested to Hyaloperonospora isolate D5 at seedling stage under controlled conditions. A significant coefficient of correlation was observed (r=0.628, P=0.000, n=36) by comparing the plants in both growth phases. In general, the accessions were more resistant at adult than at seedling stage. No accessions were resistant at seedling and susceptible at adult stage. However, two accessions with a highly susceptible response at seedling stage presented a resistant and a partially resistant response at adult phase under field conditions. Our results suggest that DM resistance observed at the seedling stage is a good indication of wild rocket resistance behaviour at field adult plant. The most promising accessions identified as resistant at seedling stage may be further exploited in breeding programmes.
- Physical mapping in a triplicated genome: mapping the downy mildew resistance locus Pp523 in Brassica oleracea L.Publication . Carlier, Jorge; Alabaça, Cláudia S.; Sousa, N. H.; Coelho, P. S.; Monteiro, A. A.; Paterson, A. H.; Leitão, J. M.We describe the construction of a BAC contig and identification of a minimal tiling path that encompass the dominant and monogenically inherited downy mildew resistance locus Pp523 of Brassica oleracea L. The selection of BAC clones for construction of the physical map was carried out by screening gridded BAC libraries with DNA overgo probes derived from both genetically mapped DNA markers flanking the locus of interest and BAC-end sequences that align to Arabidopsis thaliana sequences within the previously identified syntenic region. The selected BAC clones consistently mapped to three different genomic regions of B. oleracea. Although 83 BAC clones were accurately mapped within a similar to 4.6 cM region surrounding the downy mildew resistance locus Pp523, a subset of 33 BAC clones mapped to another region on chromosome C8 that was similar to 60 cM away from the resistance gene, and a subset of 63 BAC clones mapped to chromosome C5. These results reflect the triplication of the Brassica genomes since their divergence from a common ancestor shared with A. thaliana, and they are consonant with recent analyses of the C genome of Brassica napus. The assembly of a minimal tiling path constituted by 13 (BoT01) BAC clones that span the Pp523 locus sets the stage for map-based cloning of this resistance gene.
- The downy mildew resistance locus Pp523 is located on chromosome C8 of Brassica oleracea L.Publication . Carlier, Jorge; Alabaça, Cláudia S.; Coelho, P. S.; Monteiro, A. A.; Leitão, J. M.We have previously constructed a genetic map of Brassica oleracea L. containing the Pp523 locus that confers downy mildew resistance to adult plants. In this work, 44 SSR markers of reference for the Brassica C genome chromosomes were added to the map, allowing the nine major linkage groups to be assigned to the nine chromosomes of B. oleracea. Locus Pp523 was located on chromosome C8, and a locus determining flower colour was mapped to chromosome C3. In comparison with the first version of the map, the new map is denser and more compact. The available genomic information on B. oleracea was enriched with the chromosome location of two phenotypic traits and 421 DNA markers (RAPD, ISSR, AFLP, SCAR, BAC-end derived STS, SSR and other PCR markers). Conversely, the genomic information on B. oleracea chromosome C8 is being used as an additional tool for the map-based cloning of Pp523, the first gene for adult plant resistance to downy mildew precisely located to a specific chromosome of this crop species.