I test our ulluco varieties annually and whenever suspicious symptoms are observed.  Plants that produce our parent tubers are tested and field grown plants are randomly tested for the common viruses.  All varieties listed in the catalog have passed this testing regimen.  The tolerance is zero.  Any variety with a confirmed positive result will not be offered.  This testing program began in 2017.

Virus Method Schedule Rationale
Andean Potato Latent Virus (APLV) ELISA Once at introduction Some heirloom ullucos have tested positive for APLV in the past.  I don’t do ongoing testing because we have never seen a field positive.
Beet Curly Top Virus (BCTV) Not tested Not tested I used to test for this, but have never seen a positive result.
Broad Bean Wilt Virus 1 and 2 (BBWV1 and BBWV2) ELISA Once at introduction I tested the full collection for this virus once and got no positive results.
Comovirus genus PCR Once at introduction I suspect the presence of Ulluco Virus C in some heirloom ullucos.  I don’t do ongoing testing because we have never seen a field positive.
Cucumber Mosaic Virus Not tested Not tested I no longer test for this virus, but all of our original varieties were tested for CMV and none were positive.  If CMV infects ulluco, it is probably rare.
Nepovirus genus PCR Once at introduction Cautionary against Arracacha Virus A, but I have never seen a positive result.
Papaya Mosaic Virus (PapMV) Immunostrip & ELISA Annually Many heirloom ullucos are positive for PapMV.  I have not seen a positive result for years, but it is easy to test for, so better safe than sorry.
Potato Leafroll Virus (PLRV) ELISA Annually Some heirloom ullucos are infected.  We have PLRV in potatoes and there is some potential that it could move to ulluco.
Potato Virus S (PVS) Immunostrip Annually I have once seen a positive result for PVS in ulluco.  I’m not particularly concerned about PVS in ulluco, but I want to make sure that there is not a source of infection for potatoes.
Potato Virus T (PVT) ELISA Once at introduction PVT is present in many Andean root crops in the Andes, but I have never seen a positive result.  I will probably stop testing for this virus in seed-grown ullucos after 2020.
Potyvirus genus Immunostrip & ELISA Annually Primarily screening for Ulluco Mosaic Virus, which has probably been detected in heirloom ulluco varieties in the past.  Because potyvirus is also a group that widely infects Andean tubers, I test everything annually.
Tobamovirus genus PCR Once at introduction Screening for Ulluco Mild Mosaic Virus.  An unidentified tombamovirus was once detected in an heirloom ulluco, which was most likely UMMV.  I will probably stop testing for this virus in seed-grown ullucos after 2020.