Variation for response to Peronospora parasitica (downy mildew) and Albugo candida (white blister) in Brassica and Arabidopsis

摘要

Variation has been found among interaction phenotypes when a range of Arabidopsis thaliana (At) and Brassica accessions are inoculated with different isolates of Peronospora parasitica (Pp) and Albugo candida (Ac). In Brassica, genetic characterization of this variation is rudimentary and only one allele at a single locus associated with isolate specific resistance to Pp in B. napus has been defined. In contrast, and considering only those phenotypes that can be discriminated readily among segregating individuals, alleles controlling genotype specific variation for response to these pathogens have been identified at 21 loci (RPP and RAC) in the At genome. Most of these loci have now been mapped with varying degrees of resolution and occur in several linkage groups on 4 of the 5 At chromosomes. Progress is being made towards the isolation of these alleles using a map-based strategy. Efforts are also being made in parallel to identify and characterize equivalent genes in B. oleracea. The investigation of linkage relationships between these genes and molecular markers in both species will allow an appreciation of the collinearity of the two genomes in regions important for disease resistance. In addition, the availability of cloned gene sequences from At may allow the localization and isolation of homologous genes in Brassica, and enable the expression of At alleles as transgenes in Brassica to be investigated.