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Cellular Responses of Pine Callus to Infection by Phytophthora cinnamomi. J. C. Jang, Graduate research assistant, Department of Forestry, Clemson University, Clemson, SC 29634-1003; F. H. Tainter, Professor, Department of Forestry, Clemson University, Clemson, SC 29634-1003. Phytopathology 80:1347-1352. Accepted for publication 3 August 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1347.

The expression of differential resistance in pine callus tissues to the fungal pathogen Phytophthora cinnamomi is described. The major species groups of loblolly and loblolly ? shortleaf pine hybrids were more resistant to infection and invasion by the fungus than were shortleaf and Virginia pine. Within clones of each species, however, two separate reaction types were identified. These are designated as ?susceptible? and ?resistant.? There were several major differences between these reactions at the cellular level. Fewer hyphal penetrations, a greater accumulation of electron-dense materials, and morphological changes of the host cell wall were associated with resistant reactions. No hypersensitive reaction was evident in any inoculated callus tissues. Resistance to P. cinnamomi appears to be regulated by physiological and biochemical mechanisms.

Additional keywords: littleleaf disease.