Evolution of linked avirulence effectors in Leptosphaeria maculans is affected by genomic environment and exposure to resistance genes in host plants

Abstract

Brassica napus (canola) cultivars and isolates of the blackleg fungus, Leptosphaeria maculans interact in a 'gene for gene' manner whereby plant resistance (R) genes are complementary to pathogen avirulence (Avr) genes. Avirulence genes encode proteins that belong to a class of pathogen molecules known as effectors, which includes small secreted proteins that play a role in disease. In Australia in 2003 canola cultivars with the Rlm1 resistance gene suffered a breakdown of disease resistance, resulting in severe yield losses. This was associated with a large increase in the frequency of virulence alleles of the complementary avirulence gene, AvrLm1, in fungal populations. Surprisingly, the f..