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Histology and Progression of Fusiform Rust Symptoms on Inoculated Loblolly Pine Seedlings. E. G. Kuhlman, Principal Research Plant Pathologist, USDA Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Athens, GA 30602. . Plant Dis. 72:719-721. Accepted for publication 15 March 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/PD-72-0719.

Nine months after inoculation of loblolly pine (Pinus taeda) seedlings with basidiospores of Cronartium quercuum f. sp. fusiforme, most symptomatic tissues had necrotic cells in the cortex. When infection caused depressed areas, necrosis included xylem and phloem cells. Whereas tissues in galls longer than 10 mm were heavily and extensively colonized by the rust, tissues from galls shorter than 10 mm had rust mycelium only in small, isolated areas in the cortex, phloem, or xylem. Seedlings with no stem symptoms or with purple stem spots but no swelling when outplanted at 9 mo were symptomless 24 mo after inoculation. Seedlings with galls shorter than 10 mm at 9 mo usually were free from symptoms (6367%) after 24 mo. Seedlings with galls 1025 mm long at 9 mo had the highest frequency of galls and aecia at 24 mo, whereas those with galls 1025 mm long with depressed areas and those with galls longer than 25 mm had the highest mortality rates.