Division 1.1 Symptoms on potatoF1

The potato plant . The early stage of infection in the field is recognised by wilting of the leaves towards the top of the plant at high temperatures during the day with recovery at night. In early stages of wilting leaves remain green, but later yellowing and brown necrosis develops. Epinasty also occurs. Wilting of one shoot or whole plants becomes rapidly irreversible and results in the collapse and death of the plant. The vascular tissue of transversely cut stems from wilted plants usually appears brown and a milky bacterial ooze exudes from the cut surface or can be expressed by squeezing. When a cut stem is placed vertically in water, threads of slime will stream from the vascular bundles.

The potato tuber . Potato tubers must be cut transversely close to the heel (stolon end) or longitudinally over the stolon end. The early stage of infection is recognised by a glassy yellow to light brown discolouration of the vascular ring from which a pale cream bacterial ooze emerges spontaneously after some minutes. Later, the vascular discolouration becomes a more distinct brown and necrosis can extend into the parenchymatous tissue. In advanced stages, infection breaks outwards from the heel end and the eyes from which bacterial slime may ooze causing soil particles to adhere. Reddish-brown slightly sunken lesions may appear on the skin due to collapse of vascular tissues internally. Secondary development of fungal and bacterial soft rots is common in the advanced stages of the disease.