- Prepare silica gel (Alfa Aeser silica gel dessicant, indicating, -6+16 mesh granules) used for collecting the spores. Silica gel crystal are dried in a hot air oven (120C) for 1-2 days and allowed to cool in a dry place until color changes from blue to light pink or almost white. When dry, the silica gel crystals are stored in tightly sealed Falcon tubes.
- Collect the powdery mildew spores in the hood with the air-flow turned off. Pour silica gel crystals on the leaves with the fungal culture. Use a camel hair artist brush to spread the silica gel on the leaves and to gather them after the spores stick to the gels. Collect the silica gel using forceps. The gels with the spores are put into labeled Nunc cryostorage vials. Fill one half (1 ml) of each tube with silica gel crystals coated with fungal spores.
- The cryostorage vials are stored in vapor phase liquid nitrogen tanks at -150 to -186C.
- To test if the spores are viable after storage, collect the tubes from the vapor phase liquid tanks and spread the crystals on detached leaves of Top Mark melon, or squash. Spread the crystals with a camel hair artist brush to ensure the spores are detached from the gels and spread on the leaves. Incubate the squash leaves under normal light for a week to start seeing colonies.
