"What? Like an apple or something?" (Don Day)
"In the Irish Druid tradition, the Silver Bough is cut from a magical Apple tree, where silver apple shaped bells played a mystical tune, which could lull people into a trance state." (Tree Lore: Apple; by Susa Morgan Black) So, yes, rather like an apple but made of silver. However Anne Lister has already dismissed the apple bough with silver bells as not applicable to her question (see above)so I'll move on.

Some replies to my posting your question elsewhere, Anne, have produced the following responses. They don't give any specific references but might be a starting point if you think any are relevant.

"I'm not even sure if northern European traditions would even have any relevance to this. In those beliefs, the apple denotes long life, eternal youth, the ancestors, the magical crafts and the gods of the underworld. It's true that after the Anglo-Saxons broke through Grim's Dyke and took the South-West of Britain, part of the exodus fetched up in Galicia, establishing Britonia, as the Albiones tribe. Did their belief system survive their absorption into the general population?"

Also, (reproduced in full):
   "I suppose it depends what we mean by authority. Historically, I am not aware of any symbolism that would lend itself to this interpretation - by the time Christianity becomes the major focus of folklore, the apple tree has already taken on other connotations.
   The earliest known example I can think of - and my knowledge is by no means exhaustive! - is the apple-branch carried in The Voyage of Bran: "A branch of the apple tree from Emain / I bring, like those one knows." Why did the maiden carry this magical apple branch to the court of Bran? One thing to note is that she takes the branch with her when she leaves: "nor was there strength in Bran's hand to hold the branch." So in this case the branch is not used specifically to gain passage to the Other World (early C20th scholars leaned a little too heavily on potential parallels between Classical and Celtic myths in my opinion), as Bran sets sail without it. [*See my comment below]
   It seems to me that there are two symbols here: the baton or wand itself, and the wood from which it is made. The Mabinogi has plenty of examples of wands or batons used as symbols of authority, especially in the third and fourth branches."

*I believe though that this was yet another example of an apple branch with silver bells which was used to entrance Bran so that he followed her on a voyage to the Otherworld.

"The apple as a symbol of authority does not fit with any of my usual associations, but apart from those you have mentioned you might consider as a long shot that the father of Modron (< the Brythonic goddess Matrona) was Afallach ('apple place'). Matrona was the mother of Maponos, so the source (authority?) of these deities could be said to be the place of apples. But how that would carry through into a 12 th c. Occitan romance is unclear!"

Sorry Anne - your question seems to have remained unanswered!