Yes fungi can be stored at -80 without loosing its virulence by following methods.

1. lyophilizer (You don't have)

2. harvest the spores produced on PDA plate with cell scrapper and mix it with sterilized boric powder and store in vials under deep freeze or normal freeze.

Have you tried this method. How long we can store them

another method for maintaining the virulence of the plant pathogenic fungi can be infecting the specific plant with the fungi and after three days of its incubation plating the infected plant material on a pda plate. I have tried this for storing. It can be done for regular check on the virulence of the plant infecting organism.

Dear Padder,

I grew pathogen (eg. Pyricularia grisea) on paper discs (5-10 mm diameter) from PDA, dried in desiccator, put them in container/vial/eppendorf tube with silica gel and then kept at -80oC for about 3 years. I revived them successfully and FOUND THEM VIRULENT. The revival rate was higher if preserved in thicker paper disc (cover box of blotter paper) than thinner one (blotter paper). I do not take them out from -80oC to room temperature (25oC) directly. Preferably I put them from -80oC to 4o C before leaving lab and then work next morning. Before opening I keep the pack in safety cabinet/work bench for a while to remove moist condition over pack. This helps safe return of remaining paper disc to -80oC.

For frequent use and to keep the pathogen virulent we sometimes inoculate host and reculture.

Regards

Hossain

I would suggest to store them in 30% glycerol

Glycerol stock can be used for long time storage in deep freeze. You can use grains  of respective host plant for storage. Generally researchers use grains for mass multiplication, but it can be used for storage up to 9-12 months without loosing the virulence of pathogen..  

For a short term conservation you can store them in sterile distilled water at room temperature and in darkness; this should solve the problem of subculturing in rich media. For long term conservation you can deep freeze with glycerol 20-30%.

Also to keep the pathogen virulent you can inoculate host and reculture.

We have very good results with the Glycerol method as mentioned before. Although it does not work evenly well for all fungi. Another method that you can try similarly is to grow the fungi in a test tube with (diagonal) agar. Once fungi has overgrown the agar fill the tube with sterile liquid paraffin (oil). Store at 4°C.