I am no expert but i would say that is growth from the rootstock and should be removed.
I think i remember seeing that before myself.
Grafted model?

This post was edited by laidbackdood on Sun, Sep 8, 13 at 12:47

remove that growth straight away!! that is rootstock

Just trifoliate rootstock. Thumb off the shoots (better than cutting them off) if you can. Not a big deal. You just don't want to let the rootstock send up shoots, as it will take over your grafted cultivar (in this case, a variegated lemon, which tends to be less aggressive in it's growth habit than the rootstock it's grafted to).

Patty S.