Fruits of a rent since alteration (10)

I believe the answer is:

nectarines

I'm a little stuck... Click here to teach me more about this clue!

'fruits' is the definition.
(nectarine is a kind of fruit)

'a rent since alteration' is the wordplay.
'a rent since' anagrams to 'NECTARINES'.
But, I'm unsure how the anagram is indicated.

'of' is the link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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