Field Resistance to Potato Blight (Phytophthora infestans)

Abstract

TWO types of resistance of potatoes to blight (Phytophthora infestans) have been distinguished—‘true resistance’ by virtue of hypersensitivity (suprasensitivity) and ‘field resistance’¹. True resistance is not found in the old varieties of European cultivated potato ; but it has been bred for on an extensive scale for more than thirty years using the wild Mexican potato, Solanum demissum, as the source of genes for the hypersensitive reaction. It appears now that this hypersensitive type of resistance by itself is of limited value, because new physiological races of blight can arise very rapidly to attack clones carrying as many as four different major genes for hypersensitive reactions², and because S. demissum itself is attacked by blight in Mexico³. In contrast, field resistance, which is found in certain varieties of European cultivated potatoes and in other potato species, may be equally effective against all physiological races of blight.