Polymorphism of Avr Genes in Russian Populations of Phytophthora infestans

The oomycete Phytophthora infestans (Mont.) de Bary is a causative agent of the most harmful potato disease, late blight. The pathogenicity of P. infestans is associated with (a)virulence genes (Avr genes). Changes in the composition and nucleotide sequence of these genes lead to the emergence of new races of the pathogen, which affect potato varieties previously considered resistant. Therefore, to successfully combat late blight, it is important to study polymorphisms in Avr genes in populations of this pathogen. We conducted a large-scale molecular and phytopathological study of P. infestans strains collected in European Russia. In this study, polymorphisms of 11 Avr genes were analysed using SSCP analysis and sequencing. The genes included Avr1, Avr2, Avr2-like, Avr3a, Avr3b, Avr4, Avr8, Avr-Smira1, Avr-blb1, Avr-blb2 and Avr-vnt1. As a result, the allelic composition of Avr genes was studied and new alleles unique to Russia were identified in Russian populations of P. infestans for all studied Avr genes, with the exception of Avr4 and Avr8. The vast majority of the Avr1, Avr2-like, Avr3a, Avr4, Avr-vnt1 and Avr-Smira1 gene sequences correspond to known virulence variants of these genes that avoid recognition by the corresponding potato resistance genes. The Avr-blb2 gene was represented by approximately equal amounts of virulent and avirulent variants. Predominantly avirulent variants were found for the Avr-blb1 gene. The Avr2, Avr3b and Avr8 genes were represented only by avirulent variants. Summarising the results of our study, we can conclude that the populations of the European territory of Russia differ from the populations of Europe and the USA in the allelic composition of virulence genes. We failed to detect a dominant clonal lineage in the territory of Russia, and the Russian population of P. infestans is highly diverse.