Plant & Animal Genomes XIV Conference

January 14-18, 2006
Town & Country Convention Center
San Diego, CA

Tracking Down Pp523 And Pp1A, Two Brassica oleracea L Downy Mildew Resistance Genes

José M Leitão¹ , Mário J Farinhó¹ , Joana V Leitão¹ , Nelson F Sousa¹ , Paula S Coelho² , António A Monteiro³ , John E Bowers⁴ , James C Estill⁴ , Andrew H Paterson⁴

¹  FERN, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal

²  Quinta do Marquês, Estação Agronómica Nacional, 2780-505 Oeiras, Portugal

³  Departamento de Horticultura, Instituto Superior de Agronomia, Tapada da Ajuda,1349-018 Lisbon, Portugal

⁴  Plant Genome Mapping Laboratory, University of Georgia, Athens, GA 30602, USA

Two novel sources of genetic resistance to downy mildew in adult plants of Brassica oleracea L., Pp523 and Pp1A, were recently identified. Both resistances proved to be monogenic, dominant, and independently inherited. Starting from a recently published genetic map (Farinhó et al., 2004) where the Pp523 locus was already mapped, some additional DNA-markers linked to this locus and a group of DNA-markers linked to the Pp1A locus were identified. Five DNA-markers flanking the Pp523 were cloned and their sequences allowed the identification of a homologous and syntenic region in chromosome 1 of A. thaliana L. The screening of a B. oleracea L. genomic BAC library with “overgo” probes designed according to the same sequences allowed the identification of a set of clones constituting the extremities of the BAC contig that encompasses the Pp523 locus. A second set of BAC clones linking these two extremities was selected on the basis of a multiplex hybridisation experiment using Brassica “overgos” probes that match specific A. thaliana L. gene sequences. This first draft version of a BAC contig encompassing the Pp523 locus was additionally consolidated by fingerprinting restriction analysis. The co-segregation analysis of the resistant phenotype with the BAC end sequences, combined with the determination of the presence of resistance gene and resistance gene like sequences in the selected BAC clones will be determinant for the isolation of the Pp523 locus. The same strategy is being pursued for the isolation of the Pp1A resistance locus.