The lesions then develop into bright yellow spermogonial (conceptacle containing spermatia) pustules, usually on the upper leaf surfaces of the host plant. Spermogonial pustules may also appear on any of the above-ground plant parts, such as the stems. Within about 10 days of spermogonium formation, cup-like aecia (spore reproductive structures) erupt through the lower leaf epidermis.
The lesions then mature into vibrant yellow pustules housing spermatia on the upper leaf surfaces of the host plant, as well as other above-ground parts like stems. Within 10 days of spermogonium formation, cup-like aecia (spore reproductive structures) break through the lower leaf epidermis.