Wiktionary
n. A plant pathogenic virus of the family (taxlink Alphaflexiviridae family noshow=1 i=1) and order (taxlink Tymovirales order noshow=1 i=1), found mainly in potatoes. It is the type species of the genus (taxlink Potexvirus genus noshow=1).
Wikipedia
Potato virus X (PVX) is a plant pathogenic virus of the family Alphaflexiviridae and the order Tymovirales. It is the type species of the genus Potexvirus.
PVX is found mainly in potatoes and is only transmitted mechanically. There are no insect or fungal vectors for this virus. This virus causes mild or no symptoms in most potato varieties, but when Potato virus Y is present, synergy between these two viruses causes severe symptoms in potatoes.
Virus indexing and limited generation production of potato, which starts from disease-free tissue culture plantlets, has nearly eliminated this virus from many countries' potato supply.