Identification of two nucleotide sequence sub-groups within Potato mop-top virus.

To evaluate the variation of Potato mop-top pomovirus from potato fields, 21 isolates were collected from different Danish locations. Reverse transcription-polymerase chain reaction-restriction fragment length polymorphism (RT-PCR-RFLP) of regions of RNA2 was performed for all 21 isolates resulting in the establishment of two sub-groups of isolates. The nucleotide sequence of a region encoding part of the 'readthrough protein' of RNA2 was compared for 9 of these isolates. This sequence analysis confirmed the RT-PCR-RFLP grouping. The isolates were tested for symptom expression in indicator plants and grouped according to symptom development. No correlation between grouping based on symptom development and genotype was observed.