Phytosanitary Information for Mashua
I am still experimenting and developing a testing regimen for mashua and I do not consider our varieties to be virus free, although I have eliminated some viruses from the collection. All varieties have been through at least one round of blind virus treatment, meaning that I have cultured them on an antiviral medium, but I don’t know what viruses they had before or after that treatment. Mashua viruses are not well documented and many are not easy to test for. I suspect that most of my mashua varieties still carry some sort of mild mosaic virus, as they show symptoms during warm weather and in the senescing leaves. It is possible that this is a physiological condition, but it looks more consistent with a viral disease to me. Whatever it is, it does not appear to impact yield as far as I can tell.
Currently, I test mashua for the Potyvirus group, which covers several common mashua viruses, and for Papaya Mosaic Virus. I once tested the collection for Potato Virus T, which is the only quarantine virus known to infect mashua, finding no positives. There are many more possible viruses in mashua and probably some that are not yet identified. As time and money allow, I will continue to test the mashua collection more broadly and eliminate or clean varieties that test positive for viruses.
Because I think that there are still viruses in this crop, there is the potential for spread in the field. That means that in vitro plantlets are more likely to be virus free than tubers, although I am not confident that my plantlets are virus free either. In vitro plantlets of Cultivariable original varieties introduced in 2019 or later are likely to be virus free, as they were established in culture before being grown outdoors.