Certain aspects of resistance of plum trees to bacterial canker

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Dagnt Erikson

A detailed histological study was made of the necrotic areas induced in the stem of a resistant and a susceptible variety of plum as the result of artificial inoculations of Ps. mors-prunorum Wormald. The pathogen was found to penetrate the tissues intercellularly, causing plasmolysis of cell contents, followed by disintegration of cell walls, and gradual invasion of the bacteria. The seasonal progress of infection was followed, the maximum cankers caused by winter inoculations in the susceptible host appearing in spring. Limitation of necrosis occurs in summer, generally accompanied by the production of new tissue composed of xylem elements. Viable bacteria were isolated in autumn from those cankers in which the area of necrosis had extended into the wood cylinder beyond the limiting periderm. The difference in the nature of the injury to the tissues of the resistant trees is quantitative rather than qualitative. The significance of the apparently more efficient host mechanism of periderm production in this variety is considered. Lesions similar in histological aspect were obtained as the result of the injection of cell-free filtrates of cultures of the causal organism.

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