a.) Assessment of powdery scab (Spongospora subterranea) and PMTV on the basis of symptoms: blister-like swelling (blisters) on surface of tubers, or open pustules (pustules)
usually 2–10 mm in diameter containing powdery mass of brown to black in color.
b.) PMTV symptoms: necrotic rings on surface of infected tuber while brown arc or internal browning in tuber flesh.
c.) Mean values (A405) of four tubers of each variety with or with spraing (brown arc) symptoms. d Values (A405 nm) after overnight (c. 16 h) and 1 h at room temperature (in parentheses).