Plenodomus lingam

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canola stems with symptoms of infection by Plenodomus lingam (bottom row stems cut open) - left: susceptible cultivar, middle and right: resistant cultivars (click on image to enlarge it)
Author: Yong-Ju Huang et al.
Source: PLoS ONE (2018) vol. 13, art. e0197752

Plenodomus lingam (Tode: Fr.) Höhn. 1911

The fungus causes blackleg and stem canker of oil-seed rape (canola) and other Brassica species, mainly in temperate regions. Yield losses of up to 50% have been reported. The symptoms include small grey oval leaf lesions, basal stem cankers and root rot.

The disease cycle usually starts by airborne ascospores, dispersed by wind and rain splashes which infect the leaves. The fungus moves through the plant causing stem cankers and also forms black pycnidia on the leaves. These produce conidia which can further spread the disease. Near the end of the season the fungus forms pseudothecia which produce ascospores, the main agents of dispersal of the disease. The release of ascospores typically starts the following season but can already begin in autumn, depending on the weather conditions. The fungus can survive in plant debris as pseudothecia or saprophytically for several years. Cultural management like removing stubble and crop rotation can be effective.

Vernacular names
• Deutsch: Wurzelhalsfäule des Raps
• English: Phoma stem canker
blackleg of crucifers
stem canker of crucifers
• Español: pie negro de las crucíferas
• Français: jambe noire chez les crucifères
nécrose du collet des crucifères

Pycnidia are spherical, approximately 200-300 µm large. The conidia are cylindrical to ellipsoidal, aseptate and around 3-5 x 1-2 µm in size. Pseudothecia are round to oval, about 300-400 µm large. Ascospores have 6 cells and are 50-60 x 6-7 µm large.

Synonyms:
Leptosphaeria maculans
Phoma lingam

Taxonomic note:
The previous teleomorph name Leptosphaeria maculans has been and is still used by many authors for this fungus. For a taxonomical review see de Gruyter et al., 2013.

For details see the respective page in Wikipedia.