QTL for Resistance to Globodera rostochiensis Pathotype Ro2 and G. pallida Pathotype Pa2/3 in Autotetraploid Potato

The golden and white potato cyst nematodes ( Globodera rostochiensis and G. pallida, respectively) are devastating quarantine pests of potatoes. The most widely distributed pathotype of the golden nematode, Ro1, is well controlled by the H1 resistance gene. A pathotype that overcomes H1 , Ro2, has been detected on several farms in New York State. To map Ro2 resistance gene(s), two autotetraploid parental clones – NY121 (Ro2 resistant) and NY115 (susceptible) – along with 182 F1 offspring were genotyped with 8303 SNP markers, and the resistance of each clone to Ro2 was assessed with a greenhouse pot assay. Analysis with TetraploidSNPMap identified two Ro2 resistance QTL on chromosome 5: one QTL was located at 26 cM and explained 24.4% of the variation for resistance, while the second at 59 cM co-localized with a marker (57R) known to be tightly linked to H1 and explained 23.8% of the residual variation. Subsequent inoculation with G. pallida revealed that the chromosome 5 locus at 26 cM also conferred some resistance against pathotype Pa2/3, explaining 9.2% of the variation. A second QTL that increased susceptibility to Pa2/3 was located at 15 cM on chromosome 10 and explained 6.9% of the variation. The resistance gene(s) at 26 cM on chromosome 5 may correspond to previously described Grp1 ; a marker diagnostic for this region would be useful for applied potato breeding.