Bacterial soft rot and blackleg of potatoes—Pectobacterium carotovorum subsp. carotovorum and P. chrysanthemi.
Symptoms of soft rot include rotted tissues that are wet, cream to tan in color, and soft. Rot
begins on the tuber surface and progresses inward. Infected tissues are sharply delineated from healthy
tissue by dark brown or black margins. Shallow necrotic spots on the tubers result from infections. Rotting
tissue is usually odorless in the early stages of decay, but develops a foul odor as secondary organisms
invade infected tissue. Plants with blackleg are stunted and have a stiff, erect growth habit.
Foliage becomes chlorotic and the leaflets tend to roll upward at the margins. Stems of infected plants
exhibit an inky black decay. The base of the stem is often completely rotted. In relatively dry soil,
only the pith may show blackening. Tuber symptoms for blackleg are similar to those of soft rot.
Life cycle
Bacterial soft rot and blackleg infections are favored by high soil moisture and high temperatures. The bacteria are carried in and on seed pieces, in soil, and in water. It can also be spread by insects and enter growth cracks or any injury. During and after harvest, soft rot is favored by immature tubers, adverse temperatures, mechanical damage, and free water on tuber surfaces.
SolutionsAvoid planting in extremely wet soil, provide good drainage, and do not overirrigate. Use high quality,
pathogen-free tubers for seed and avoid excessive hilling when planting. Avoid excessive soil moisture
before harvest to reduce infection; harvest mature tubers with well-set skins and avoid mechanical injury.
Use clean water to wash potatoes and avoid water films on tuber surfaces during storage. Eliminate cull
piles and potato volunteers in rotation crops. Avoid susceptible varieties.
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Rotted flesh caused by bacterial soft rot
Rotted tissue caused by bacterial soft rot
Black stem caused by blackleg
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