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White Rust of Crucifers Caused by Albugo candida

Symptoms of White Rust on Shepherd's Purse

The pustules of white rust have mostly broken through the epidermis of the host and have a powdery appearance. The younger pustules at the top right (arrows), however, are still covered by the leaf epidermis. Masses of colourless (hyaline) sporangia produced by the fungus give a white, powdery appearance to the pustules.

Other crucifers attacked include broccoli, cabbage, cauliflower, celery, radish,   rutabaga, and turnip

 

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  Micrograph showing asexual stage of Albugo candida with chains of sporangia produced inside a white rust pustule.  Why do I call these conidia-like structures sporangia and not conidia?

Images from MYCOALBUM CD by George Barron