Genetic and physical mapping of the RPP13 locus, in arabidopsis, responsible for specific recognition of several Peronospora parasitica (downy mildew) isolates

Fifteen isolates of the biotrophic oomycete Peronospora parasitica (downy m ildew) were obtained from a population of Arabidopsis thaliana plants that established naturally in a garden the previous year. They exhibited phenoty pic variation in a set of 12 Arabidopsis accessions that suggested that the parasite population consisted of at least six pathotypes. One isolate, Mak s9, elicited an interaction phenotype of flecking necrosis and no sporulati on (FN) in the Arabidopsis accession Nd-1, and more extensive fitting necro sis with no sporulation (PN) in the accession Ws-2. RPP13 was designated as the locus for a single dominant resistance gene associated with the resist ance in Nd-l and mapped to an interval of approximately 60 kb on a bacteria l artificial chromosome (BAC) contig on the lower arm of chromosome 3. This locus is approximately 6 cM telomeric to RPP1, which was previously descri bed as the locus for the PN interaction with five Peronospora isolates, inc luding resistance to Maks9 in Ws-2. New Peronospora isolates were obtained from four other geographically distinct populations of P. parasitica. Four isolates were characterized that elicited an FN phenotype in Nd-1 and mappe d resistance to the RPP13 locus. This suggests that the RPP13 locus contain s either a single gene capable of multiple isolate recognition or a group o f tightly linked genes. Further analysis suggests that the RPP11 gene in th e accession Rld-0 may be allelic to RPP13 but results in a different recogn ition capability.