Recessive and dominant genes interfere with the vascular transport of Potato virus A in diploid potatoes

Resistance to Potato vines A (PVA) was examined in a diploid cross involvin g Solanum tuberosum subsp. andigena as a resistance source. Hypersensitive resistance (HR) to PVA cosegregated with extreme resistance (ER) to Potato vines Y conferred by the dominant gene Ry(adg) on chromosome XI. Hence, HR to PVA was controlled by a novel, dominant resistance gene closely linked t o Ry(adg), or Ry(adg) recognized both viruses but conferred a different typ e of resistance to each virus. The HR prevented systemic infection with PVA following mechanical inoculation but not following graft inoculation. Anot her, recessive gene, ra, that may be linked or even allelic with Ry(adg) fu lly blocked vascular transport of PVA in graft-inoculated plants. Hence, a possibility exists that the genes for the three types of resistance to poty viruses may reside at the same, resistance gene-rich chromosome region synt enic in solanaceous species and might be related. The gene ra acted against all of the three PVA strains tested and, therefore, the avirulence determi nants could not be mapped. However, also, PVA strain-specific resistance wa s found in the progeny. It was overcome by mutations introduced into the vi ral genome-linked protein and the helper component proteinase and/or the co at protein.