Potato ring rot

The disease is a bacterial vascular bundle disease, which is characterized by dwarf and wilting of aboveground stems and leaves and annular rot of underground tubers along the vascular bundle ring. The early and severe disease leads to the death of seedlings; most of the diseased plants grow slowly, dwarf and thin, few branches, small leaves, and wrinkle but not spread; if the disease is late and light, the plant height, leaves and branches grow normally, but the top leaves become smaller. In the later stage, the first or second branches or the whole plant wilted. The symptoms are most obvious after flowering, the lower leaves wilt, droop and die at first, and the upper leaves roll inward from the edge, showing dehydration, turning grayish green, and then gradually yellowing from the leaf edge to the center or veins, and finally withering at the yellow place. Near harvest, the diseased plant died early, but most of the withered leaves did not fall off, and the stem was still green. Cross-section of the stem, the vascular bundle of the stem base becomes yellowish brown, squeezed with the hand, can overflow milky sticky bacterial pus. Potato pieces are not easy to show symptoms when harvested, and only the tail is slightly reddish brown. After storage, the color of the potato skin darkened and the tail was obviously reddish brown. When you cut the potato pieces, you can see that the subcutaneous vascular bundle ring has turned light brown. Seriously diseased potatoes can be squeezed by hand, which can overflow yellow bacterial pus. In severe cases, the cortex and medulla are separated, and the epidermis burst. The pathogen is a variety of potato ring rot caused by Michigan stick bacteria. The bacteria are short rod-shaped, without flagella, solitary or occasionally in pairs, and do not form capsules and spores. Gram staining was positive. On the culture medium, the colony was white, thin, transparent and shiny.