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Effects of Heterobasidion annosum on Radial Growth in Southern Pine Beetle-Infested Loblolly Pine. S. A. Alexander, Assistant professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061; J. M. Skelly(2), and R. S. Webb(3). (2)Professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061; (3)Former graduate research assistant, presently assistant professor, School of Forest Resources and Conservation, University of Florida, Gainesville 32611. Phytopathology 71:479-481. Accepted for publication 19 September 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-479.

The association of Heterobasidion annosum with reduced radial growth was observed in loblolly pine (Pinus taeda) infested with southern pine beetle (SPB) (Dendroctonus frontalis). Plots with SPB and controls were established in thinned plantations and natural stands of loblolly pine. Only sites infested with SPB for less than 8 wk were selected for experimental evaluation. A control plot was established 20 m from each SPB plot. Trees infested with SPB produced an average of 6% less radial growth over the last 15 yr in the loblolly pine plantations as compared to the noninfested control plots (P = 0.05). Mean H. annosum colonization of excavated root systems in SPB and control plots in plantations were 23.1 and 10.9% (P = 0.05), respectively. Within the plots infested with SPB located in plantations, the SPB-infested trees produced 28% less radial growth for the last 15 yr, respectively, as compared to the noninfested trees (P = 0.01). Mean H. annosum colonization of excavated root systems in SPB-infested and noninfested trees in the SPB plots were 54 and 11% (P = 0.0001), respectively. It was concluded that loblolly pines preferred by SPB were being stressed by H. annosum prior to SPB attack and that this stress was being expressed through reduced radial growth.

Additional keywords: annosum root rot, Fomes annosus, radial growth, bark beetle, predisposition.