Seed tubers infected with PMTV transmit the disease to roughly half of their daughter tubers. The other half remains healthy. Not all daughter tubers infected in the
field show symptoms at harvest. Infected tubers that appear healthy at harvest develop symptoms in storage.
Rust-brown, necrotic arcs or rings and flecks form in the flesh of infected tubers that show symptoms. There may be single or multiple concentric arcs. These symptoms are called “spraing.” On very susceptible varieties, raised concentric rings of 1–5 cm in diameter develop on the tuber surface.
Laboratory and greenhouse tests are required for correct identification of the potato mop top virus.
