So I'm looking into something called landrace gardening. To do this, you start out with multiple cultivars of an edible crop then let them cross pollinate, creating new cultivars. Of those new cultivars, you then select the best to save seed from. In theory, by doing this over and over again, you will have developed a/many culivar(s) that have adapted to your specific garden and can grow great there.

My question is: We know time-honored cultivars are edible but "could" the cross pollination that occurs between to edible cultivars create toxic off-spring? Is that likely or something to be worried about?