IDENTIFICATION OF THE CLUBROOT RESISTANCE GENE RPB1 AND INTROGRESSION OF THE RESISTANCE INTO CANOLA BREEDING LINES USING A MARKER-ASSISTED APPROACH

A total of 955 Brassica accessions were screened against Plasmodiophora brassicae pathotype 3 and a total of 35 accessions showed >50% of reduction in clubroot severity relative to a susceptible control under controlled conditions, with four B. rapa and one B. nigra accessions demonstrating complete resistance. The accession FN (B. rapa subsp. chinensis) was of particular interest due to its ability to resist each of five pathotypes of P. brassicae identified in Canada. A cross between FN and a susceptible canola (B. rapa) line resulted in a segregating F₁ population with a 1:1 segregation ratio, indicating the resistance is based on a single dominant gene. A total of 318 microsatellite markers were screened and 104 polymorphic markers used to analyze a 1299 F₁ plant population for mapping of the resistance gene. This gene, designated as Rpb1, was flanked by the markers sN8591 and sR6340I at 0.54- and 0.77-cM distance, respectively. These markers were proved to be effective for marker-assisted selection during introgression of the resistance gene into B. napus and B. rapa canola breeding lines.