White Rust of Crucifers Caused by Albugo candidaSymptoms 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
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