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Resistance

Evaluation of Pathogenic Variability of Cronartium fusiforme on Loblolly Pine in the Southern USA. H. R. Powers, Jr., Chief Research Plant Pathologist, U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Carlton Street, Athens, GA 30601; F. R. Matthews(2), and L. D. Dwinell(3). (2)(3)Principal Research Plant Pathologists, respectively, U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Carlton Street, Athens, GA 30601. Phytopathology 67:1403-1407. Accepted for publication 10 May 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1403.

Isolates from 56 individual rust galls from seven southeastern states were used to inoculate three loblolly pine families rated as resistant, intermediate, and susceptible to infection by Cronartium fusiforme. Significant variation appeared among the rust collections from different states and among collections within individual states. Even the most resistant pine family was highly susceptible to infection by inocula from certain individual galls. Because this high variability occurred in a limited sample of the fungus population, it is clear that pathogenic variability of the fungus should be taken into account in all tree-improvement programs involving southern pines. The high levels of virulence of specific inocula, even on resistant hosts, also mean that efforts must be intensified to find new sources of resistance, and to develop a wide genetic base of resistant pine material in breeding programs.

Additional keywords: Pinus taeda, fusiform rust, disease resistance, southern pines.