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Seedling Inoculations with Fomes annosus Show Variation in Virulence and in Host Susceptibility. E. G. Kuhlman, Principal Plant Pathologist, Southeastern Forest Experiment Station, USDA Forest Service, Forestry Sciences Laboratory, Research Triangle Park, North Carolina 27709. Phytopathology 60:1743-1746. Accepted for publication 3 July 1970. DOI: 10.1094/Phyto-60-1743.

Variation in the virulence of 23 isolates of Fomes annosus to nursery-run Pinus taeda was demonstrated by inoculating seedlings with infested beech branch segments. Most of the isolates caused 85-100% mortality of P. taeda seedlings; however, four of the isolates caused only 50-60% mortality. The isolates reacted similarly in several trials on P. taeda. Variation in host susceptibility was shown on conifer and hardwood species with 10 isolates of the fungus. On coniferous hosts the average mortality was: P. elliottii var. elliottii, 82%; P. echinata, 80%; P. taeda, 74%; P. virginiana, 72%; Abies fraseri, 67%; P. palustris, 65%; P. strobus, 64%; and Juniperus virginiana, 28%. Conifers other than J. virginiana appeared to be highly susceptible to F. annosus. In a second trial with P. elliottii var. elliottii, P. palustris, and P. taeda seedlings, the average mortality was 72, 64, and 63%, respectively. When seedling mortality due to F. annosus is a factor in regeneration of pine plantations, these results indicate there would be little advantage in favoring one pine species over another. Essentially no mortality of the hardwood species, Liriodendron tulipifera or Plantanus occidentalis, occurred due to F. annosus.