Infectious sap of alfalfa mosaic virus (AMV), inoculated mechanically in different diagnostic plants, reacted positively with each tested plant. Symptoms ranged from local as local lesions in case of Phaseolus vulgaris L., to systemic as severe systemic yellow mosaic in case of Petunia hybrida L. Infectivity of King Edward potato cultivar was confirmed with Enzyme Jinked immunosorbent assay (ELISA), Dot blotting immuno-binding assay (DBIA), and Immunosorbent electron microscopy (ISEM). Infected samples reacted positively in comparing with control treatment. Six AMV ­ infected potato cultivars were positive in ELISA test when examined with AMV antiserum. Gigant was the highly susceptible cultivar, meanwhile Diamant was the lowest susceptible one. Direct electron microscopic examination of crude sap containing AMV showed types of AMV particles ranged from spherical to bacilliform. Some particles were in aggregates. Ultra-transverse thin sections showed some changes in cell structures, such as degradation in mitochondria membrane and swelling of chloroplasts, which contained big vacuoles. Electron microscopy studies revealed the presence of virus particles in mitochondria, cytoplasm and nucleus. Ultra-transverse thin sections in potato leaves produced from tissue culture technique showed normal cell structures.