VIEW ARTICLE

Cytology and Histology

Ultrastructural Changes Induced by Scutellonema brachyurum in Potato Roots. Andrew C. Schuerger, Former graduate student, Department of Plant Pathology, University of Arizona, Tucson 85721; Michael A. McClure, professor, Department of Plant Pathology, University of Arizona, Tucson 85721. Phytopathology 73:70-81. Accepted for publication 28 May 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-70.

Within 12 hr after Scutellonema brachyurum began to feed on potato roots, dark brown lesions were initiated, which eventually extended several hundred micrometers axially in the root. Lesions involved cells not directly penetrated by S. brachyurum, which suggested a chemical as well as mechanical injury to tissue. Feeding was always intracellular and was generally restricted to epidermal and cortical cells. Ultrastructural alterations of potato root tissue occurred only in cells directly penetrated by S. brachyurum. An extensive membranous network surrounded the stylet in penetrated cells and appeared to originate from the plasmalemma, which invaginated around the stylet during penetration. Dense spherical inclusion bodies, which were interspersed in the membranous network, resembled material in the stylet orifice and buccal cavity of the nematode. Where the stylet penetrated the cell wall, a feeding plug formed that appeared to be continuous with material in the buccal cavity. Longitudinally arranged “macrotubules” of various diameters (20- 40 nm, averaging 30 nm) occurred in groups of up to 25 in penetrated potato root cells. A residual matrix containing small, tightly packed spherical bodies was observed in root tissue parasitized for longer than 48 hr. It is believed that the residual matrix was the final stage of cytoplasmic degeneration. Bacteria were found only in cells disrupted by the nematode.