Potato Ring Rot

a bacterial disease that affects the vascular tissue of potatoes.

The causative agent is Corynebacterium sepedonicum. The leaves of diseased plants turn yellow and wilt; if the infection is severe, the entire plant dies. When the tubers are cut, creamy yellow rings of affected vascular tissue, which later turn black, are visible in the early stages of the disease; there is also a yellowish mucoid mass of bacteria. Potato ring rot progresses while the potatoes are in storage. Another form of the disease— yellow pitted rot—arises as a result of the infection of healthy tubers while they are being harvested and manifests itself in March and April. Small round depressions with decayed, yellowed flesh appear on the tubers. Control measures consist in selecting healthy planting material, planting potatoes in whole tubers, cultivating resistant varieties, and carrying out general agrotechnical measures for improving the condition of plants.