Exploiting Knowledge of Pathogen Effectors to Enhance Late Blight Resistance in Potato

Late blight disease of potato, caused by Phytophthora infestans, is the most serious disease of this crop on a global scale and is thus a threat to food security. Use of resistant potato cultivars to prevent late blight does not have a very successful history, as P. infestans genotypes have overcome the deployed resistances. Thus, there is a need to identify more durable resistances, or identify and develop novel forms of resistance that exploit vulnerabilities in the biology of P. infestans. Application of molecular biology tools in P. infestans research has recently culminated in the identification of several avirulence effectors matching specific resistances in potato, the sequencing of the P. infestans genome and identification of hundreds of candidate translocated pathogen 'RXLR' effector proteins that may promote disease progression. Strategies for prioritising these effectors for further research are revealing those that are highly expressed during infection, difficult for the pathogen to alter rapidly, essential for P. infestans pathogenesis and recognized by resistant accessions of Solanum spp. These effector characteristics are being used to identify and characterise resistances from Solanum germplasm that may prove more durable. In addition to RXLR effectors, P. infestans also produces a broad spectrum of additional secreted proteins. These are exposed to plant cells and may potentially act to trigger resistance, either as broad spectrum pathogen-associated molecular patterns or as specific effectors of resistance. Alternatively, conserved secreted proteins may be attractive targets for novel agrichemical development. We have silenced a diverse selection of these candidate secreted proteins in P. infestans and demonstrated their effects on late blight disease development. Results from these studies are aiding a deeper understanding of P. infestans disease development and identifying potential pathogen weaknesses for exploitation in future control measures.