Breeding Pears for Resistance to the Pear Scab Fungus Venturia Pirina Aderh.

Three clones of Venturia pirina have been tested for their pathogenicity towards forty varieties of cultivated pear. From observations on the reactions of these forty varieties, twelve were selected for differentiating the pathogenicity of sixteen clones of the fungus. These tests differentiated four main groups of biotypes of V. pirina. Clones isolated from Conference showed wide differences in range of pathogenicity. One isolate from Conference was shown to parasitize six of the most widely grown pears in England: other Conference biotypes had a narrow range. No variety of pear was found immune to all the isolates. Beurré Giffard was lightly infected by an isolate from Durondeau, but was resistant to all the other isolates tested.