DURABLE CISGENIC RESISTANCE TO PHYTOPHTHORA INFESTANS IN POTATO AND PERSPECTIVES FOR APPLICATIONS IN AFRICA

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 to introduce a combination of natural resistance genes into a potato cultivar in principle 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 Phytophthora infestans (Rpi), Rpi-sto1 (Solanum stoloniferum), Rpi-vnt1.1 (S. venturii) and Rpi-blb3 (S. 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 in the greenhouse. Selected clones were tested in field trials in The Netherlands and Belgium in 2011 and 2012 in comparison with the susceptible parent Désirée, and other susceptible and resistant cultivars. In both years the plots were not treated with fungicides against Phytophthora infestans. In contrast to the summer of 2011, the summer of 2012 was very humid resulting in a 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 twenty resistance genes against Phytophthora 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 much 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.