Sequence analysis of the rDNA-ITS regions from these isolates identified three Anastomosis Groups (AGs), AG-3PT, AG-2-1 and AG-5. Isolates classified as AG-3PT were widely distributed, whereas AG-2-1 and AG-5 were confined to distinct locations. Sequence heterogeneity was identified in the ITS regions of 100 AG-3PT and AG-2-1 isolates. Variation in the sequence and length of the rDNA-IGS1 region was also observed for selected isolates of AG-3PT and AG-2-1 isolates. Phylogenetic studies found all AG-2-1 isolates belong to AG-2Nt, a subset of AG-2-1 previously associated with solanaceous crops in other countries. AG-2-1 isolates were consistently more aggressive than those of AG-3PT. Delayed emergence, severe infection on stolons, formation of aerial tubers and considerable yield losses were associated with AG-2-1, but they caused negligible black scurf. In contrast, AG-3PT caused black scurf on progeny tubers but variable effects on stem emergence and stolons. Furthermore, AG-2-1 isolates caused severe tuber malformation, but isolates of other AGs did not