Durable cisgenic resistance to Phytophthora infestans in potato and perspectives for applications in Africa

Late blight caused by Phytophthora infestans is a major constraint in potato production. A promising strategy to combat late blight in potato is to combine different resistance genes to achieve durable resistance. Resistance genes from wild relatives can be introduced by breeding or by transformation. Single resistance genes are not durable because mutant pathogens that avoid recognition will easily be selected. Genetic engineering is a straightforward method allowing introduction of a combination of natural resistance genes into a potato cultivar without altering other agronomic characteristics. Since these genes can also be introduced by conventional breeding methods, the resulting potato plants are called cisgenic, in contrast to transgenic potatoes that have received DNA from non-crossable species. Three R genes conferring resistance to P. infestans (Rpi), Rpi-sto1 (Solanum stoloniferum), Rpi-vnt1.1 (Solanum venturii) and Rpi-blb3 (Solanum bulbocastanum), were cloned and transformed separately or as a combination into the susceptible cultivar Désirée. The transformed clones were screened for late blight resistance using a detached leaf assay, and they were also evaluated for true-to-type performance under greenhouse conditions. To evaluate the performance of the resistance genes or combinations in realistic conditions, selected clones were tested in field trials in The Netherlands and Belgium in 2011 and 2012. This was done in comparison with the susceptible parent Désirée, and other susceptible and resistant cultivars. In both years plots were not treated with fungicides against P. infestans. In contrast to 2011, the summer of 2012 was humid resulting in high natural disease pressure. Nevertheless the two seasons showed similar results with clear differences between the susceptible reference clones and the genetically modified resistant clones. About 20 resistance genes against P. infestans have currently been mapped or cloned and more will follow. Therefore a collection can be generated of double or triple R gene-containing resistant cultivars that have the potential to make potato cultivation more sustainable. Based on the current potato cultivation area in East Africa, the effect of using cultivars with durable resistance on increasing potato yield in East Africa can be predicted