Blackleg (potatoes)

The term "blackleg" originates from the typical blackening and decay of the lower stem portion, or "leg", of the plant.

Blackleg appears as a black discoloration of previously healthy stems, accompanied by a rapid wilting, and sometimes yellowing, of the leaves.

However, in some cases of early disease development, mature stems may turn yellow and wilt even before black decay is evident.

[1][4] Disease symptoms are not necessarily uniformly exhibited from both shoots originating from a single tuber or in a field infested with P. atrosepticum.

[3] This is partly explained by the narrow environmental conditions needed for pathogenicity, although new findings in research are showing strong evidence of density dependent quorum sensing signals used by P. atrosepticum in exhibiting virulence.

Buildup of tuber contamination is limited by reducing the number of field generations of these seed potatoes to 5 to 7 years.

Additionally, it is critically important to keep the potatoes at a low temperature with adequate aeration and humidity control in order to minimize development of the pathogen in infested stocks.

These pathways include the control of the production of plant cell wall degrading enzymes in addition to other virulence factors.

Research indicating the role of other soil microbes in degrading P. atrosepticum quorum sensing communication molecules provides the possibility for safe and effective control of the disease.

Washington State University, which has posted a large comprehensive list of potato cultivars available in North America, only calls out two blackleg susceptible varieties: Monona and Superior.

Varieties with resistance values of 6-9 on a scale of 1-9 include Avondale, Axona, Bonnie, Cara, Emma, Isle Of Jura, Orla, Osprey, Sarpo Mira, Saxon, Sebastian, Vales Sovereign.