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Mycologia, MASTIGOMYCOTINA, PERONOSPORALES, PYTHIACEAE .

Crops attacked: walnut .

Collar rot, ink disease

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

[R]Description
This fungus forms an infective complex with P. cambivora and P. cinnamomi .
It causes withering of the outer leaves and the drying out of the top shoots which causes a gradual death of the branches starting with the topmost ones. Usually a lesion occurs at the base of the trunk out of which a dark watery liquid exudates.

[R]Biology
This pathogen survives in the soil for several years as oospores.
In the proximity of the walnut roots the oospores germinate and zoosporangia produce zoospores which attack the roots. The mycelium develops and invades the whole root system, then the collar. P. cactorum is mainly an intercellular pathogen which colonizes the parenchyma. The vascular tissues become dark.

[R]Epidemiology
The disease is favoured by the excessive humidity of the soil in winter. Oospore germination occurs at 10 -12 °C. and zoospores need free water to disseminate. The disease is spread by running water, irrigation or splash.

[R]Treatement
Check import of healthy seeds or seedlings.
Use resistant cultivars.
Moderate irrigation is recommended.

[R]Possible misleading
P. cambivora and P. cinnamomi which cause the same symptoms.

[R] Images

1. Phytophthora sp. , Ink disease (DESPREZ-LOUSTAU M-L., INRA)
   Ink disease on chestnut-tree Ink disease of chestnut-tree.
   

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

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