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Blackleg (potatoes)
Blackleg is a plant disease of potato caused by pectolytic bacteria that can result in stunting, wilting, chlorosis of leaves, necrosis of several tissues, a decline in yield, and at times the death of the potato plant. The term “blackleg” originates from the typical blackening and decay of the lower stem portion, or “leg", of the plant.〔De Boer S. H. 2004. ("Blackleg of potato" ). The Plant Health Instructor. DOI:10.1094/PHI-I-2004-0712-01〕
Blackleg in potatoes is most commonly caused by ''Pectobacterium atrosepticum'' (older synonym: ''Erwinia carotovora subsp. astroseptica''), a gram-negative, nonsporulating, facultative anaerobe that is also associated with soft rot of potatoes. While other bacterial species such as ''Pectobacterium carotovorum'' and ''Dickeya dadantii'' can exhibit symptoms similar to blackleg of potato, these pathogens exhibit broader host ranges, are present in different climates, and typically are more associated with soft rot diseases.〔〔Ali HF, Ahmad M, Junaid M, Bibi A, Ali A, Sharif M, Ali B, Nawab K, Sadozai A. 2012. Inoculum Sources, Disease Incidence and Severity of Bacterial Blackleg and Soft Rot of Potato. Pakistan Journal of Botany 44:825-830.〕
==Symptoms and signs==
Early blackleg symptoms develop in the growing season soon after the plants emerge. They are characterized by stunted, yellowish foliage that has a stiff, upright habit.〔〔 The lower part of the below ground stem of such plants is dark brown to black in color and extensively decayed. When infected, the pith region of the stem is particularly susceptible to decay and may extend upward in the stem far beyond the tissue with externally visible symptoms. Young plants affected by blackleg are particularly susceptible, typically dying after a halt in development.〔
Blackleg symptoms may develop in more mature plants during the later part of the growing season, and are distinguished from those that develop earlier in the season. Blackleg appears as a black discoloration of previously healthy stems, accompanied by a rapid wilting, and sometimes yellowing, of the leaves. Starting below ground, black discoloration moves up the stem, often until the entire stem is black and wilted. However, in some cases of early disease development, mature stems may turn yellow and wilt even before black decay is evident. However, after the entire stem exhibits disease symptoms, the wilted plant can be lost from view in the healthy potato plant canopy.〔〔
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