BACTERIAL CANKER OF SWEET CHERRY IN THE NIAGARA PENINSULA OF ONTARIO: PSEUDOMONAS SPECIES INVOLVED AND CULTIVAR SUSCEPTIBILITIES

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Abstract
Bacterial canker of sweet cherries in the Niagara Peninsula of Ontario is caused by at least two species or physiotypes of Pseudomonas bacteria. Biochemical tests indicated that the species are similar to English isolates of P. morsprunorum Wormald and P. syringae van Hall. Pathogenicity tests on nine sweet cherry cultivars and on seedlings of apple, pear, peach and mahaleb and mazzard cherry indicated that Ontario P. morsprunorum and P. syringae isolates are pathogenically distinct. Comparative tests with English and Ontario isolates indicated close pathogenic similarities among isolates of P. morsprunorum, whereas isolates of P. syringae appeared to be distinct races. Susceptibility trials with sweet cherry indicated that Ontario grown cultivars are sufficiently sensitive to both bacterial species to consider the disease a serious problem in cherry production. Moreover, the existence of at least two pseudomonas species in Ontario with distinct pathogenicity patterns in sweet cherry indicates that breeding for resistance will be a difficult task.