Phytophthora infestans: a review of past and current studies on potato late blight

Phytophthora infestans is the causal agent of potato late blight. Genotypes of Japanese populations of P. infestans have been classified as US-1, JP-1, JP-2, JP-3, and JP-4 based on analyses of DNA polymorphisms. These populations may have been introduced to Japan by the migration of P. infestans from other countries and by domestic changes produced through sexual and asexual propagation. Resistance to late blight has been an ongoing desire of potato farmers in Japan and elsewhere. Recurrent backcrossing of Solanum demissum to varieties of S. tuberosum has been used to transfer late blight resistance. Many varieties carry the R1 gene, whereas others carry R2, R3, and/or R4. However, R genes provided only transient resistance to late blight. New races rapidly overcome R-gene-mediated resistance. The R genes of potato generally encode receptors that recognize secretory effector (Avr) proteins produced by P. infestans. These effector proteins induce robust resistance in potato varieties containing R genes, while they suppress resistance in potato varieties lacking R genes. Conserved molecules from Phytophthora species such as fatty acids, glucans, and elicitins also act as elicitors in Solanaceae species. These P. infestans-derived elicitors induce defensive reactions, including the accumulation of phytoalexins and hypersensitive cell death. A future challenge will be to combine our accumulated knowledge with that from other scientific fields to develop a disease management approach for late blight.