There was actually another discussion besides the one you provided.
What Ted Petit does is he does not spray his plants while they are seedlings and lets them get rust to see which ones are more resistant. I would assume that somewhere along the way these were done the same way.
You would really have to email Greg or Ted for more info because there is more to it than what you find on the Internet. He explained it at our regional meeting but I was so busy with behind the scenes stuff I didn't get to listen to his whole presentation where he talked about these plants.
