Effects of Oxidant Air Pollution on Susceptibility of Pine Roots toFomes annosus

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Abstract
Oxidant air pollution injury to foliage of ponderosa [Pinus ponderosa Laws.] and Jeffrey [P. jeffreyi Grev. and Balf.] pines increased the susceptibility of roots to infection and colonization by F. annosus under field and fumigation chamber environments. Roots of ponderosa pine trees severely injured by oxidant air pollution became infected proximal to the inoculation point significantly more often than did roots of healthy trees. Proximal colonization rate of F. annosus in inoculated ponderosa pine also was much greater in trees severely affected by air pollution. Exposure of container-grown ponderosa and Jeffrey pine seedlings to ozone in fumigation chambers increased infection and colonization by the pathogen. More seedlings (78% of both species) fumigated with ozone were infected than were nonfumigated seedlings (62 and 53% for ponderosa and Jeffrey pine, respectively). Colonization of host tissue of both species by F. annosus was directly related to ozone dose and seedling injury. These results indicate a very substantial, probable effect of oxidant air pollution on the rate of increase of F. annosus in coniferous forest stands subjected to chronic injury.