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Cytology and Histology

Histopathology of Fusarium moniliforme var. subglutinans in Four Species of Southern Pines. Jane Barrows- Broaddus, Plant pathologist, USDA Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Carlton Street, Athens, GA 30602; L. D. Dwinell, principal plant pathologist, USDA Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Carlton Street, Athens, GA 30602. Phytopathology 73:882-889. Accepted for publication 17 November 1982. 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, 1983. DOI: 10.1094/Phyto-73-882.

New shoots formed on 1-yr-old Virginia (Pinus virginiana), slash (P. elliotii var. elliotii), loblolly (P. taeda), and pond (P. serotina) pines were wounded and inoculated with Fusarium moniliforme var. subglutinans, the causal agent of pine pitch canker. Seedlings were sampled for histological examination and for colonization by the pathogen 1, 4, 12, 26, 35, and 56 days after inoculation. After 56 days, the remaining trees were rated for shoot mortality and lesion development. Active lesions on Virginia and slash pines had more continuous resin flow and more extensive purple discoloration along the stem than those on loblolly and pond pines. Fusarium moniliforme var. subglutinans rapidly grew intercellularly through the cortex of all host species. The pathogen attacked parenchyma cells throughout the stem, causing gaps in the cortex, rays, and pith. Infection in the cortex of Virginia and slash pines tended to be diffuse and was not delimited by boundary tissues such as a periderm, but in loblolly and pond pines, infected areas were bounded by a periderm, which created the appearance of a discrete lesion. Disease progression was arrested in the first node below the inoculation point where the fungus was contained in cortical tissue surrounded by stem and lateral bud tracheids. Virginia and slash pines had a higher percentage of resin ducts forming tylosoids than loblolly and pond pines. More layers of regenerative parenchyma were observed in the xylem in inactive lesions of loblolly and pond pines than in Virginia and slash pines. Lignification of pith cell walls was observed in all species, but was more prevalent in inactive lesions in loblolly and pond pines. Primordial sporodochia were observed in Virginia pine in axils and sheaths of buds emerging directly below a dead shoot.