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Infection and Colonization of Different Organs of Slash Pine Seedlings by Cronartium fusiforme. Thomas Miller, Plant Pathologist, Southeastern Forest Experiment Station, USDA Forest Service, Athens, Georgia 30602; Ellis B. Cowling, Professor of Plant Pathology and Forest Management, Department of Plant Pathology, North Carolina State University, Raleigh, North Carolina 27607. Phytopathology 67:179-186. Accepted for publication 24 August 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-179.

Slash pine seedlings ranging from 17 days to 4.5 mo old were inoculated with precast basidiospores of Cronartium fusiforme at predetermined locations on different organs to determine susceptibility of the organs at several ages and patterns of colonization by the fungus. Hypocotyls, stems, cotyledons, and primary and secondary needles all were susceptible at certain ages. Percentage infection of all inoculated organs decreased with increasing age. Stem galls developed following inoculation of all organs except secondary needles. Average longitudinal growth of the fungus in infected organs was relatively uniform for a given organ, but growth of the fungus in the hypocotyls and stems after 7 or 8 wk was more than double that in the foliar organs. Patterns of colonization of the different organs by C. fusiforme are described.

Additional keywords: Fusiform rust, Pinus elliottii var. elliottii, histology.