The update said four Canterbury properties had been confirmed to have the virus.
Further testing, including soil testing, was being undertaken to determine whether 10 additional farms are infected with the virus, not 18 as earlier reported. Soil testing takes a number of weeks to complete.
MPI said the virus was not a food safety issue.
The first infected potato was found during routine sampling of material at a chip processing facility.
Biosecurity New Zealand and Potatoes New Zealand launched a joint response on September 19.
The virus, which causes distortions to the potato skin, deep cracking, rust-coloured arcs and streaks in the tuber flesh, is spread by soil-borne fungus but survives long-term in the potato plant or fungus. If established in fields, its spores can survive up to 20 years in the soil.
Biosecurity NZ said if widespread, it could cause productivity issues for growers.
Anyone with a symptomatic potato please call 0800 80 99 66 or email PMTV2018Liaison@mpi.govt.nz