As promised earlier, I have found out more about the HRI research - not yet complete.
They are ridding white rot by getting large amounts of onion scales (this is the edible bit, as I understand it, not the paper-like outer). They suggested I could get some from storage at the end of winter that are starting to go to seed from a friendly veg merchant.
Cook it at 50 degrees centigrade for half an hour. Put the mixture about two inches thick over the infected area at the time you would usually put your sets out in the spring.
Apparently, the white rot spores seem to think there are nice fresh onions to rot, and by the time they discover it is just sterilised onion with nothing for them to rot, it is too late and the spores die. Not yet commercially available, but the scientists seem reasonably confident about it.
