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Histopathology of Pinus ponderosa Ectomycorrhizae Infected with a Meloidogyne Species. Jerry W. Riffle, Principal Plant Pathologist, Rocky Mountain Forest and Range Experiment Station, Forest Service, USDA, Albuquerque, New Mexico 87101; Phytopathology 63:1034-1040. Accepted for publication 9 February 1973. DOI: 10.1094/Phyto-63-1034.

An undescribed Meloidogyne sp. was found infecting ectomycorrhizae of mature Pinus ponderosa in southwestern New Mexico in 1963. Nematode larvae penetrated the ectomycorrhizae, migrated to the stelar region, and developed into adults with their heads embedded in vascular tissues. As the female developed, cortical cells and the associated Hartig net at and near its body were compressed and collapsed. Fungal mantles were ruptured, and a gelatinous matrix containing many nematode eggs protruded from the mantle surface. Giant cells developed as a cluster of multinucleate cells in the vascular tissues immediately adjacent to the head of the nematode. Cytoplasm of actively functioning giant cells was dense, very granular in texture, and contained greatly enlarged nuclei with irregularly lobed membranes. As the giant cells became senescent, their cytoplasm became highly vacuolated, deteriorated, and cavities usually appeared in vascular tissues originally occupied by the giant cells. Xylem tracheids in the immediate vicinity of the giant cells were distorted, crushed, and even scattered in irregular isolated patches.