Varietal differences in susceptibility to potato virus Y

In addition to giving different kinds of symptoms when infected with potato virus Y, individual potato varieties also differ in their susceptibility to infection, in the concentration of virus attained in their sap, and in their efficiency as sources of virus for aphides. Their relative susceptibility in the open when exposed to equal chances of infection is correlated with the ease with which they become infected when colonized with infective aphides, and can be assessed from tests made under glass. Methods for making such tests are described; these need few tubers and give reproducible results. It is considered that they could be applied in studying the inheritance of this type of resistance and to test the behaviour of new seedlings. The American variety Katahdin was the most resistant of those tested, but there were significant differences between commercial British varieties. In the open, all varieties were equally colonized by aphides and resistance to infection with virus Y was not correlated with resistance to leaf roll.