Strain Variation in Pear Blister Canker Virus

Williams’ Bon Chretien pear trees inoculated with blister canker virus varied in symptom expression. Plants propagated from buds of mildly affected trees showed only slight symptoms while those raised from severely affected trees developed severe canker. Tests indicated that mildly affected plants contained a virus which protected them against the effects of a more virulent strain.

Williams’ Bon Chretien trees developed symptoms when infected with virus from any one of three sources ; Doyenne du Comice and Laxton’s Superb developed symptoms when inoculated with two of the virus sources, but not with the third. Infected Beurre Hardy, Conference and Fondante d’Automne trees were symptomless and latent infection was detected in a symptomless Quince C plant. Inoculation of apple and quince varieties indicated no relationship between pear blister canker and other virus diseases of pear, quince or apple.