Making cross with an unstable (F3) line...

[tpeltan]

Originally Posted by crmauch

I would say if you know specifically what you are breeding for, it would be better to start with stable varieties that have the genetics you're looking for.

There might be an exception if you want something you can't obtain by simple crossing of existing stable lines. Your initial F2 (F3) generation might combine several important traits for further breeding on one parent(e.g. disease resistance...) and then you add the other parent for further desirable traits.