CHEMOTHERAPY OF APPLE STEM PITTING AND PEAR STONY PIT WITH RIBAVIRIN

Three young 'Virginia Crab' apple trees recently bud-inoculated with stem pitting and individual branches of two mature 'Beurré d'Anjou' pear trees systemically infected with stony pit were treated with 500 ppm ribavirin, a guanosine analogue, by weekly foliar application throughout the growing season. Near the end of the treatment period, healthy 'Spy', 'Virginia Crab' and 'Beurré d'Anjou' indicator trees were bud-inoculated with buds from present-season growth of the treated trees.

Typical stem pitting and stony pit symptoms developed on untreated control trees, on untreated parts of the infected pear trees and on indicator trees budded with buds from the untreated trees and tree parts. Treated trees and tree parts and indicator trees budded with buds from these trees and tree parts remained symptom-free during the first season following treatment. In the second year, symptoms reappeared in some treated parts of the systemically infected 'Beurré d'Anjou' trees. The results indicate that ribavirin inhibits the replication of the stem pitting and stony pit agents and prevents their systemic movement.

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