FIGURE 2.

Symptoms of bacterial ring rot caused by Clavibacter sepedonicus on potato tubers. On intact tubers, surface cracks and dark blotches immediately beneath the periderm become visible (a). The surface of the severely infected tubers turns reddish‐brown (b). Milky exudate can sometimes be squeezed from wilted stems near the point of attachment to the tuber seedpiece (c). Ring rot symptoms can be observed by cutting the tuber longitudinally through the heel end where the tuber was attached to the stolon (d). When the tuber is gently squeezed, pillars of cheese‐like material emerge from the vessels (e). In the case of severe infection the two parts of the cortex may be separated and the entire tuber ultimately can rot (f)