Identification of the corresponding avirulence gene of Leptosphaeria maculans to the resistance gene (LepR1) in Brassica napus

Blackleg of canola is the most important disease of canola/rapeseed worldwide. Efforts are made to understand the host-pathogen interaction by studying the interaction between resistance genes of the host and the avirulence genes of the pathogen. Previous studies showed that two double haploid canola (Brassica napus L.) lines, ddm-12-65-1 and ddm-12-65-2, possess a novel resistance gene (LepR1) against PGT (99-43 & 99-56) and PG2 (WA-74) isolates. However, these two lines are susceptible to PG2 isolate 87-41. It is thought that the avirulence of isolates WA-74, 99-43 and 99-56 on the lines ddm-12-65-1 and ddm-12-65-2 is governed by the Avr1/LepR1 and the virulence of isolate 87-41 is governed by avr1/LepR1. Isolates 87-41 and 99-56 were selected as virulent and avirulent isolates based on phenotypic reactions caused by the isolates on the lines and their mating type. They were crossed and the progenies segregated based on the phenotypic reaction on the line ddm-12-6-1. The 87-41 × 99-56 L. maculans map will be constructed using PCR-based markers including single sequence repeats (SSR) and sequence related amplified polymorphic (SRAP) markers. Polymorphic bands will be recorded as present or absent in the parents and in the whole progeny. Once the physical distances of the Avr gene with its markers are identified, the genomic BAC library from L. maculans isolate 99-56 will be constructed. The library will be screened using the closely linked markers and a combination of markers could then be used to identify positive clones.