everyone
i know that replate flasking is when you thin or transplant the protocorms from the mother flask.
but how do you do this without contamination.
shahrez
In a laminar flow cabinet/sterile chamber just as you do when you sow the mother flask. As you're transferring sterile protocorms to a sterile flask (with sterile tools) contamination is usually less of a problem than when first plating disinfected seed. Replating serves two purposes. As you mentioned it thins the protocorms to allow space to grow. It also provides fresh/differently formulated media to the protocorm improving growth and removing potentially inhibitive compounds needed for germination. If you don't flask plants yourself, commercial flasking labs should offer a replating service.