Towards Durable Resistance by Stacking Broad Spectrum Cisgenic Resistance Genes

Introduction The potato (Solanum tuberosum) originated from South America and is now the third largest crop in the world, after rice and wheat. Potato is a cross pollinated and vegetatively propagated crop, with a genome size around 840 MB, which was recently sequenced. Most potato cultivars are autotetraploid, with breeding programs lasting for 12–15 years. Among many biotic and abiotic stresses to potato, late blight, caused by the oomycete Phytophthora infestans (Pi), is particularly devastating. Pi was the cause of the Irish potato famine in the 1840s, and presently causes millions of dollars of loss annually1. Long-term solutions to this disease focus more on breeding for host resistance using resistant potato germplasm rather than on spraying large amounts of chemicals. Not only are chemical sprays environmentally unfriendly, the mutation rate of the pathogen may also result in chemical resistance.