Translation:The largest apple producer in Brazil lives here.
"The largest producer of apples in Brazil lives here" would be correct; the singular 'apple' does not work in this sentence.
Aren't "apple producer" and "producer of apples" synonyms? If you don't like the term "apple producer" that's fine but I can't see any reason why it's wrong. Ford is a producer of cars but many sources refer to the company as a car producer.
Sure. But by the same token it wouldn't be 'producer of apple' or 'apples producer'.
Oh sorry, when you said the singular "apple" does not work in this sentence I thought you meant the English one because you supplied an alternative English sentence that uses "apples" instead. I believe "maça" can be reasonably translated as "apples" here.
Is there a rule for deciding the best way to parse this kind of sentence that has a "de ... de ..." structure?
In English I can imagine two sentences "The largest apple producer in Brazil lives here" (accepted and what I put) or "The largest producer of Brazilian apples lives here" which I'm not sure works.
Also, another question, does "mora == lives" work here? If they are talking about a company rather than a person there must be a better word. If they are really talking about a person then he or she must be very tall, fat or both.
"Morar" is more colloquial, used more often than "viver" (onde você mora? - moro na Alemanha.) The sentence you quoted would be "o maior produtor DE maças brasileiras (or "maça brasileira") mora/vive aqui." Now, if it was related to a company we'd probably say: "a maior empresa produtora de suco(s) de maça (apple juice) fica/é aqui" (better to use "ficar")
That was my question too (see earlier in the discussion) and it was answered by Paulenrique (although he probably meant to say "aqui" rather than "no Brasil").