Includes bibliographical references (leaves 108-123).xi, 123 leaves : ill., photos ; 26 cm.The comparative studies carried out suggest that tomato aspermy virus and the Q strain of cucumber mosaic virus are sufficiently similar to be included in the same taxonomic group. Nevertheless, the two viruses are distinct and the present nomenclature should be retained.Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Pathology, 197