Master Gardener: What causes some citrus fruit to split?

Q: I’ve noticed that some of the navel oranges on our tree have rind that is splitting vertically from the navel to the stem.  Why?
A: It’s disappointing to see your long-awaited crop of navel oranges begin to split as the harvest season approaches.  Even commercial growers can experience this frustrating situation, and it can occur on other types of citrus too, not just navel oranges. The good news is that this is not the fault of a disease or insect.  Instead, f