Latent Colonization and Pathogenicity ofHypoxylon atropunctatumon Oaks

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Abstract
Decay of phloem and sapwood by H. atropunctatum, and stromata of this fungus that developed on inoculated and girdled oak trees were not associated with inoculation wounds. The fungus was recovered with equal frequency from discolored sapwood beneath inoculated and control wounds. H. atropunctatum was isolated from branches of 57% and trunks of 11% of healthy-appearing oaks. Isolation frequencies from black and white oaks were similar. Girdling of 196 uninoculated, healthy-appearing trees resulted in the development of H. atropunctatum on 77% of the black and 70% of the white oaks within 5 mo. Latent colonization probably accounts for the rapid increases in disease incidence following drought. The greater natural incidence of disease on black oaks than on white oaks may be related to host differences in drought sensitivity.