Thanks for the info. I actually emailed Kelly Winterton yesterday having read his Potato Onions page ( http://sites.google.com/site/kellysgarden/potato-onions
). And thanks to the information he's provided, I'm now trying to get hold of the 'Yellow Potato Onion' that he started with. I think I've found it at Gatersleben Genebank along with some other 'Allium cepa L. Aggregatum' accessions that may be of use.
If receive these accessions I may be able to try breeding my own line, something that was on the cards if I could get 'Green Mountain' as we are fond of red (purple) onions in our family. I'm hoping that planting some red Allium cepa bulbs amongst the potato onions and letting all them go to flower will facilitate a cross. Perenniality is apparently a dominant trait in onions so with a little luck it should be possible. I'm actually considering adding some 'Mammoth Onions' ( http://www.mammothonion.co.uk/shop/2/index.htm
) to the mix to see just how big potato onions can be breed.
Kelly also provided me with contact info for someone in the UK that has received 'Green Mountain', and Green Mountain seeds, so I may well be able to obtain some starts.
I don't know why I keep adding breeding projects to my plate, it's stuffed full already, but these large potato onions that Kelly's created look well worth the effort.