A recent question on Skeptics SE, brought up an interesting debate on the origin of this proverb.
Particularly, in the comments to this answer we were wondering whether apple really refers to the specific fruit of Malus domestica or it indicates a generic fruit/vegetable.
The OED and various Google searches seem to indicate that apple was used to generically indicate any round fruit, and that is unsurprising, seen its symbolic meaning.
The discussion came from the fact that the Italian version of the proverb, una mela al giorno leva il medico di torno, also refers to an apple (mela), although in Italian -at least to my knowledge- mela does not generally refer to a round fruit (there is a term, pomo, which has that meaning, but it is not used in the proverb).
Moreover, the first report of this proverb in English seems to date back to the mid 19th century, although some (rather dubious, if you ask me) Wikipedia page refers to a XII century medical conference in Salerno as a possible source.
Anyone can shine some light on the matter? Which version came first? What does apple mean in this case?
Bonus question: is there a reliable source for looking at the meaning/derivation of proverbs?