VIEW ARTICLE

Histopathology of Oxidant Injury and Winter Fleck Injury on Needles of Western Pines. Paul R. Miller, Plant Pathologist, Pacific Southwest Forest and Range Experiment Station, Forest Service, USDA, Berkeley, California 94701, stationed at Riverside, California; Lance S. Evans, former Postdoctoral Fellow, Department of Biology, University of California, Riverside 92502, Present address: Biology Department, Brookhaven National Laboratory, Upton, New York 11973. Phytopathology 64:801-806. Accepted for publication 27 December 1973. DOI: 10.1094/Phyto-64-801.

In comparison of ozone injury, total oxidant injury, and a winter fleck injury of pine needles, no histological difference was found between the two air pollutant injuries in ponderosa pine needles. In both, injury was confined to the mesophyll cells, especially those nearest the abaxial needle surface, and no other cell types were affected. Needles collected from remote areas free of oxidant air pollutants, and from areas where oxidant damage is known, both showed necrotic flecking of only the abaxial needle surface. In tissue with winter flecks, principally the mesophyll cells, but also endodermal, transfusion, and vascular cells were affected. Hyperplasia in the endodermis and transfusion area, was common only with winter fleck. No detailed account of the development of the winter fleck can be derived from histological evidence, but fleck symptoms are distinctly different from those of ozone, total oxidant, fungus infection, and sucking insects. The presence of winter fleck in needles exposed to snow suggests that the condition may be best characterized as winter weather injury.