Alfalfa mosaic virus (AMV) was previously identified as the casual agent of internal tuber necrosis in a potato cultivar. To further characterize the isolate (CaM), it was inoculated to seven potato cultivars. Sporadic needle-sized necrotic spots occurred on the inoculated leaves of four cultivars. Thereafter, yellowish spots started to appear on the newly emerged leaves; which may be coupled with the needle-sized necrotic spots, depending on cultivars. As time progressed, the calico symptoms become more profound whereas the necrotic spots remained unchanged. All tubers of CaM-infected Innovator and Shepody plants developed sporadic necrotic spots in tuber flesh. So did ~23% and 8% tubers of CaM-infected Yukon Gold and Rochdale Gold-Dorée, respectively. Sequence analysis of the CP gene of CaM with that of other potato isolates indicated that CaM shared >97.1% sequence identity with all but four Egyptian isolates. Phylogenetic analysis of all available sequences demonstrated that RNA1 and RNA3 can be grouped into three major clades each whereas RNA2 can be clustered into two clades. Interestingly, CaM and Ca175-1, an isolate that was deemed non-necrotic in a previous study, had different phylogenetic clade patterns, indicating different RNA1-RNA2-RNA3 haplotypes: IA-I-IB (CaM) vs. Ca175-1 (IB-II-IA). Despite the differences, CaM and Ca175-1 induced similar levels of internal necrosis in tubers of Innovator and Shepody. The results suggest that the internal necrosis in AMV-infected tubers depends on potato cultivars rather than on AMV strains/haplotypes.