To address the question (vs. somehow addressing proprietary genetics), how they can do it (get a presumed US and/or is this an EU trademark)? is that despite Amyamous' claims of preexisting common use, there simply appears to be no evidence supporting this -- "AutoDuck" has apparently has not been in general use (enough) previously for the name to in any way be considered in the public domain (not trademarkable). For example, do a Google search on "autoduck," and the only cannabis-relevant entries retrieved are for the Dutch Passion seeds. That's now pretty rare for most any such meaningful word combination.
If you have any significant relevant evidence of prior use, depending on country, 3rd parties can or can't easily challenge granted trademarks. In the U.S., aren't trademark decisions disclosed for 6-months public comment prior to granting? Any breeder wanting AutoDuck for itself simply should have commercially used that name before Dutch Passion did and left some retrievable evidence of this, and that alone would have killed granting of the trademark to Dutch Passion.
Otherwise, what's the problem, sensitivities, with seed trademarks? It's only these exact names used for related commercial purposes (cannabis seeds) that are covered, and anyone can use these names all they want to refer specifically to the Dutch Passion seeds. Trademarks have nothing to do with patent protection (granting of commercial exclusivity) for inventions.
Of course, Dutch Passion should patent its seeds and their genetics every way it can (which increasingly involves less and more limited coverage/protection than most assume), including any unique gene sequences conferring AutoDuck's unique phenotype. They clearly invented something new here; and if they legally deserve and get a patent, then ideally they should license their AutoDuck breeding technology to other seed companies or themselves exclusively promote their new invention -- that's just how commerce works. [And otherwise, patents on such things as cannabis seeds are just for show, not readily enforceable or defended from challenge, rather than actually providing protection from any serious competition. But with AutoDuck seeds, I doubt there is anything patentable (in the US)].