© 1969 by Institute of Chartered Foresters
Peridermium pini (Pers.) Lev. and the Resin-top Disease of Scots Pine
II. Lesion Anatomy
Forestry Department, University of Aberdeen
The stages in the formation of Peridermium pini lesions are described. The hyphae of the parasite were septate, uninucleate, and intercellular, with unbranched haustoria penetrating all phloem cells and xylem parenchyma cells. Lesion extension occurred by apical growth of the hyphae along the outer edge of the functional phloem. The hyphae stretched unbroken across the active cambium. Active centripetal and longitudinal growth of the mycelium occurred in the resin ducts of the xylem, the hyphae commonly reaching the pith. Spermogonia were produced in late summer and fall, aecia appeared in spring. In lesion xylem, tracheids were shorter, rays taller, more numerous and wider, but ray cell height remained unchanged. Fusiform rays increased in number and size and vertical resin ducts increased in number. Changes in xylem tissues did not become evident until two to four years after invasion of the cambium by the mycelium. Invasion of the secondary phloem resulted in an increase in number and size of the longitudinal phloem parenchmya cells, while changes in phloem rays were similar to those in xylem rays.