Bacterial Ring Rot of Potato
Bacterial ring rot of potato, caused by the bacterium Clavibacter michiganensis subsp. sepedonicus, is a serious issue for seed potato production. The presence of the disease is one of the main reasons for rejection of seed potatoes from certification programs. This disease, if left unchecked, can spread quickly through an operation leading to severe losses.
Ring rot symptoms may not be noticed until later in the growing season. Affected plants stems and leaves will wilt, start yellowing, and die. Ordinarily the lower leaves will be affected first with rolled margins and a pale yellow color appearing between the leaf veins. However, the most diagnostic characteristic appears in the tubers. The disease gets its name from the characteristic breakdown of the vascular tissue ring in the tuber. Splitting tubers in half toward the stem end reveals a yellow to brown discoloration of the vascular tissue, located approximately ¼ inch below the surface of the tuber. The discolored area often has a cheesy appearance and when squeezed a milky ooze leaks from the discolored area.