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The Histopathology of Alfalfa Roots Infected by Hoplolaimus galeatus. Oi- Cheng Ng, Former graduate student, Department of Plant Pathology, Rutgers University, New Brunswick, NJ 08903; T. A. Chen, professor, Department of Plant Pathology, Rutgers University, New Brunswick, NJ 08903. Phytopathology 75:297-304. Accepted for publication 30 July 1984. 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, 1985. DOI: 10.1094/Phyto-75-297.

Pathological changes in axenically cultured alfalfa roots infected by a single Hoplolaimus galeatus were studied by light and electron microscopy. Five days after inoculation, cell damage extended far beyond the stylet; damaged cells could be traced up to 105 μm away from the sites of nematode penetration in a longitudinal direction. Damaged cells within the lesion stained more intensely than healthy cells or cells from noninfected control tissues. Mechanical damage to the cortex was caused by formation of passageway and feeding cavities by the nematode. Although cells with dense tonoplast or darkened granular contents were also observed, these changes were probably not due to mechanical damage. Hypertrophy and early division of host cells in the pericycle were observed shortly after nematode feeding began. As the pericycle cells increased in size and number, the endodermis flattened and collapsed. Electron-dense material accumulated along the tonoplast in the cells in the endodermis and pericycle of infected roots. Vascular damage included feeding cavities, lysed phloem tissue, and the association of electron-dense material with the xylem elements. Thus, both mechanical and chemical injuries are involved in the pathogenesis of Hoplolaimus galeatus.