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Etiology

Two Flexuous-Rod Viruses in Dioscorea floribunda: Symptoms, Identification, and Ultrastructure. S. S. Hearon, Science and Education Administration, Federal Research, U.S. Department of Agriculture, Beltsville, MD 20705; M. K. Corbett(2), R. H. Lawson(3), A. G. Gillaspie, Jr.(4), and H. E. Waterworth(5). (2)Department of Botany, University of Maryland, College Park, MD 20742; (3)(4)Science and Education Administration, Federal Research, U.S. Department of Agriculture, Beltsville, MD 20705; (5)Plant Protection Institute, Beltsville, MD 20705. Phytopathology 68:1137-1146. Accepted for publication 30 December 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1137.

A naturally infected Dioscorea floribunda plant with greenbanding and mosaic symptoms contained two viruses. One, which was mechanically transmissible and designated dioscorea latent virus (DLV), produced no macroscopic symptoms in yams, but formed inclusions that resembled those formed by several potexviruses. The second virus produced greenbanding and mosaic symptoms in yams and was transmitted mechanically and by aphids. This latter virus, which was designated dioscorea greenbanding virus (DGBV), induced the formation of pinwheel and nuclear associated inclusions. Additional hosts for DGBV were not found. The modal length of DGBV varied from 600-720 nm depending on the method of extraction and preparation of particles for electron microscopy. No relationship was found between DGBV and dasheen mosaic, pepper mottle, or sugarcane mosaic viruses. In systemically infected leaves of plants infected with DLV and DGBV, DGBV was found primarily in yellow tissue. These yellow sectors had no differentiated palisade cell layer. Both the yellow and the green tissue contained DLV. Virions of DLV and DGBV were found between the arms of pinwheel inclusions in doubly infected cells. Particles of DLV were 7-9 nm in diameter, whereas DGBV particles were 9-11 nm in diameter.