Using of broad spectrum resistance genes against P. infestans for breeding new potato cultivars suitable for organic agriculture preliminary results from Ecobreed project.

Potato late blight, caused by Phytophthora infestans Mont. de Bary, is one of the most important problems for both, conventional and organic potato growers. Since fungicide protection is not possible in organic agriculture, the only way to combat with this pathogen is growing of resistant cultivars. However, the number of cultivars combining good level of agronomical characteristics with very high level of late blight resistance is still far insufficient. In the frame of Ecobreed project 65 potato cultivars hypothetically suitable for organic conditions were selected and assessed in terms of its resistance against late blight. Among these cultivars only 17 showed very high level of late blight resistance which allows to grow them without chemical protection. All these cultivars possess an R genes, which are considered to be highly effective since provide resistance against broad spectrum of P. infestans races. Unfortunately, in most cases these genes appeared in cultivars singly (or combined with low-effective R-genes) which can decrease durability of effective resistance provided by such genes. It is believed that pyramiding of the broad-spectrum resistance genes can help to produce potato cultivars durably resistant to late blight, because it is less likely for a pathogen to simultaneously gain virulence towards a plant with several highly effective R-genes. Therefore, donors of various broad-spectrum resistance genes were crossed, and progenies with pyramided R-genes were selected. Since phenotypical selection of such genotypes requires use of many different isolates of the pathogen, the use of marker assisted selection (MAS) was also applied. This method proved to be highly effective in selection of potato individuals combining two or more R-genes and will be broadly applied in the next stages of Ecobreed project.