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Variation in the Aggregation Forms of Alfalfa Mosaic Virus Strains in Different Alfalfa Organs. Roy D. Wilcoxson, Professor, Department of Plant Pathology, University of Minnesota; Lois E. B. Johnson(2), and F. I. Frosheiser(3). (2)Research Assistant, Department of Plant Pathology, University of Minnesota; (3)Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, St. Paul, MN 55108. Phytopathology 65:1249-1254. Accepted for publication 5 June 1975. DOI: 10.1094/Phyto-65-1249.

The aggregation of two strains of alfalfa mosaic virus (AMV) was studied by electron microscopy in leaves, embryonic cotyledons, ovary walls, ovules, anthers, pollen, and bud receptacles of two alfalfa (Medicago sativa) clones. No differences were attributable to the clones. Aggregation forms varied with the virus strain and the alfalfa organ where it was located. Strain F1 formed aggregations that were different from those formed by U21 in leaves, bud receptacles, and embryonic cotyledons, but not in ovary walls, anthers, or pollen. Strain F1 was usually nonaggregated in leaf cells, and sometimes in bud-receptacle cells. It formed rafts of short particles in leaves, anthers, and pollen. In pollen, the rafts formed star-like aggregations. Large crystalline bodies formed in ovary walls, bud receptacles, and embryonic cotyledons. Strain U21 usually formed aggregations in leaves, bud receptacles, and pollen, but some nonaggregated particles also formed. Rafts of short particles formed in leaves, anthers, pollen, and embryonic cotyledons. Large crystalline bodies of long particles formed in ovary walls, bud receptacles, and embryonic cotyledons. The virus was seen only in cytoplasm of parenchyma cells, transfer cells, and vascular parenchyma cells; it was not associated with cell organelles. No AMV particles were observed in ovules.