After 7 days of growth in an appropriate chamber, observe each seed for presence of slow growing circular colonies of dense white or cream mycelium that will often cover the infected seeds. Colony reverse is yellow/brown becoming darker with age.
From ISTA's Common Laboratory Seed Health Testing Methods for Detecting Fungi:
White to grey, loose, fluffy mycelium, which is characteristic of the fungus, develops on seed and in most cases without the formation of oycnidia. Whenever pycnidia develop, they are observed mainly on the filter paper below and around the seed. They appear almost transparent, sometimes with more than one ostiole. Rarely pycnidia may be produced on the seed. The ooze of pycnidiospores is pinkish.
Pycnidiospores hyaline, 1-3 septate, cylindrical, 15-32 x 2-4μm.
