Multilocus Sequence Analysis of Selected Housekeeping- and Pathogenicity-Related Genes in Venturia inaequalis

The relationship between housekeeping and pathogenicity-related genes and virulence or avirulence towards the primary Malus resistance genes (R) has not been previously studied for Venturia inaequalis fungus, the causal agent of apple scab. In this study, the sequences of two housekeeping genes encoding elongation factor alpha (EF-1α) and β-tubulin and two previously unstudied effector genes of V. inaequalis from mannosidase and glucosidase families of 100 strains collected from apple cultivars with Rvi6, Rvi1, and Rvi17 and without known scab resistance genes were submitted to the analyses. Based on the phylogenetic and diversity data, as well as recombination analyses of the sequenced regions, we assessed the phylogenetic relationships and genetic structure of the pathogen within the species and the evolutionary forces that are currently acting upon this microorganism. The topology of the obtained phylograms demonstrates the lack of a relationship between the phylogenetic position of the strain and the host cultivar and the geographical origin or race of the strain. The isolates from different hosts were differentiated but did not form diagnosable, distinct phylogenetic groups. These results suggest that the analyzed genes may be too conserved to reflect the adaptation of pathogens to apple genotypes with different R genes; thus, they do not adequately reflect race discrimination. In contrast, based on variation and gene flow estimation, genetic divergence was observed among strains virulent to apple trees containing Rvi6. The results of this study confirmed a lack of free recombination between strains and demonstrated that the analyzed regions are in linkage disequilibrium and contain non-random polymorphisms associated with the strain.