Archivio Journal of Plant Pathology

Abstract:

The development of the olive knot disease was studied taking into consideration the anatomical changes in the different parts of inoculated twig tissues, the genesis of knots and the defense reactions of the plant. At the inoculation site, bacterial inoculum invaded the cortical parenchyma, moving into the intercellular spaces and degrading the primary cell walls. The proliferation and advance of the pathogen into the different tissues of the twig was accompanied by the hyperplastic activity of parenchyma cells in affected tissues, resulting in the development of the knot. The knot was made up of hyperplastic cells, numerous cambia, and xylem elements of different origins. Cells with lignified walls surrounded bacterial cavities and the outer surface of the knots was surrounded with new periderm. At later stages of knot development, hyperplastic activities of new tissue masses exerted pressure on the periderm at the surface of the knot and induced fissures that cracked open to the outside exposing bacterial cavities.