Powdery scab
Broad Bean Botrytis.jpg
Chocolate spot on broad bean leaves
Scientific Classification
Domain: Eukaryota
Kingdom: Rhizaria
Phylum: Cercozoa
Subphylum: Endomyxa
Class: Phytomyxea
Genus: Spongospora
Species: Spongospora subterranea

Powdery scab, is a disease that occurs in potato tubers, caused by the protozoa Spongospora subterranea.


Symptoms include small lesions in the early stages of the disease, progressing to raised pustules containing a powdery mass. Powdery scab has a cosmetic effect on tubers, which can result in rejection of potatoes. The powdery pustules contain resting spores, which release anisokont zoospores which can infect the root hairs of potatoes or tomatoes.

They are generally seen on tubers as circular 5-8 mm in diameter but may be irregular in shape and lager when infection coalesce. The lesions may be sallow or deep pitted.


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