Spraing is a disease of potato tubers that causes brown streaks in the flesh of the potato. Spraing can be caused by two viruses, tobacco rattle virus (TRV) which is transmitted by trichodorid nematodes, or potato mop top virus (PMTV) transmitted by the powdery scab fungus Spongospora subterranea. The two viruses may have synergistic effects in di...