ORGANIZATION OFGENESCONTROLLINGDISEASERESISTANCE IN THEPOTATOGENOME

Abstract

Nineteen single dominant genes (R genes) for resistance to viruses, nematodes, and fungi have been positioned on the molecular map of potato using DNA markers. Fourteen of those genes are located in five "hotspots" for resistance in the potato genome. Quantitative trait loci (QTL) for resistance to late blight caused by the oomycete Phytophthora infestans, to tuber rot caused by the bacterium Erwinia carotovora ssp. atroseptica, and to root cyst nematodes have been identified on all 12 potato chromosomes. Some QTL for resistance to different pathogens are linked to each other and/or to resistance hotspots. Based on the genetic clustering with R genes, we propose that some QTL for resistance have a molecular basis similar to single R genes. Mapping potato genes with sequence similarity to cloned R genes of other plants and other defense-related genes reveals linkage between candidate genes, R genes, and resistance QTL. To explain the molecular basis of polygenic resistance in potato we propose (a) genes having structural similarity with cloned R genes and (b) genes involved in the defense response. The "candidate gene approach" enables the identification of markers highly useful for marker-assisted selection in potato breeding.

Marker-assisted combination of major genes for pathogen resistance in potato

“…A second, independent locus Sen1-4 has been identified on potato chromosome IV (Brugmans et al 2005), which may be responsible for the wart resistance alleles originating from Ry126 and Ry62. Sen1 and Ry adg are both located in the same 'hot spot' for pathogen resistance on the distal end of the long arm of potato chromosome XI, which is syntenic with the N locus in tobacco for resistance to tobacco mosaic virus (Gebhardt and Valkonen 2001). Resistance to PVY and wart also did not co-segregate in the families H98A, B, C and D (Table 3), indicating that different, non-allelic genes encode the two resistance traits.…”

“…Over the past 15 years, a number of these resistance factors introgressed in previous decades has been located on the potato molecular linkage map using DNA-based markers. They were mapped either as major genes (R genes) or as quantitative resistance loci (QRL; reviewed in Gebhardt and Valkonen 2001). The knowledge of map position and closely linked DNA-based markers now facilitates to trace and combine resistance factors from different sources, using as parents resistant genotypes from the corresponding mapping populations.…”

The novel, major locus Rpi-phu1 for late blight resistance maps to potato chromosome IX and is not correlated with long vegetation period

“…Besides the markers on potato chromosome IX, the population 97-30 was analyzed for 194 sequence-speciWc markers located on the other 11 potato chromosomes, chosen preferentially from map regions previously described as having QTL for length of vegetation period and/or resistance to P. infestans (Gebhardt and Valkonen 2001;Gebhardt 2004;Visker et al 2005). After ampliWcation and CAPS and SSCP analyses, 20 markers were polymorphic in population 97-30.…”

Using SNP markers to dissect linkage disequilibrium at a major quantitative trait locus for resistance to the potato cyst nematode Globodera pallida on potato chromosome V

“…This QRL is tagged by the DNA markers GP21 and GP179 Xanking a genetic interval of 3 cM (Meksem et al 1995). This region of the potato genome is known as a hot spot for qualitative and quantitative resistance factors to various pathogens (reviewed in Gebhardt and Valkonen 2001). One of the resistance factors in the GP21-GP179 interval is the R1 gene for resistance to Phytophthora infestans causing late blight, which is a member of a clustered gene family having a CC (coiled coil), a NB (nucleotide binding) and a LRR (leucine rich repeat) domain (Ballvora et al 2007).…”