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Mycologia, FUNGI IMPERFECTI, SPHAEROPSIDALES, PHOMACEAE .

Crops attacked: lucerne, .

Black stem of lucerne

Identification, Description, Biology, Epidemiology, Treatement, Possible misleading, Images

[R]Description
Round brown to black spots occur on the stems and the petioles, become elongated and girdle the whole organ reaching 10 cm long.
Small angular brown purple spots on the leaves.
Necrosis of the petioles can cause severe defoliation in the crop.
In late season the flowers, then the pods are attacked.

[R]Biology
The fungus overwinters in the soil on crop debris as pycnidia or chlamydospores. It also survives in the seeds after infection of the host pods.
In spring pycnidia become mature and release the pycnidiospores in a jelly dispersed and spread by rain.
Pycnidiospores contaminate the young stems which show symptoms within 3-4 days. Pycnidia form later on the dead tissues fallen on the ground.
There are several contamination cycles in one year but the first one causes the most severe loss.

[R]Epidemiology
Pycnidia become mature as soon as the average temperature reaches 5 -6 °C.
Pycnidiospores are spread by the rain and the wind.
Temperature at 15 °C. and free water on the leaves are favourable conditions for the development of the disease.

[R]Treatement
Use treated seeds.

[R]Possible misleading
.

[R] Images

1. Phoma medicaginis , Black stem (ANGEVAIN M., INRA)
   Black stem on lucerne Symptoms on stems of lucerne.
   

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HYP3 on line : Species (scientific name), Diseases (common names), Glossary, Crops.

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