Potato virus Y resistance gene, Rychc, mapped to the distal end of potato chromosome 9

A Japanese leading cultivar 'Konafubuki' has an extreme resistance gene Ry(chc) to Potato virus Y (PVY) in a simplex fashion. To reduce complexity of the highly heterozygous autotetraploid genome and map the Ry(chc) gene, haploid plants were parthenogenetically induced from 'Konafubuki'. The ratio of 7 resistant: 5 susceptible haploids confirmed the single dominant, simplex genotype of 'Konafubuki'. A selected resistant haploid 98H20-5 was crossed with a susceptible diploid, resulting in 119 F-1 plants. Using RFLP and RAPD markers, Ry (chc) was mapped to the most distal end of the chromosome 9 where the recovery of recombinant genotypes was extremely reduced in this mapping population possibly due to the linked inferiority factor. The location of Ry (chc) is different from those of the other extreme resistance genes to PVY, but possibly resides in one of resistance gene clusters.