Fruit's ascendant in Siciliano lemonade (5)
I believe the answer is:
melon
'fruit's' is the definition.
(melon is a kind of fruit)
'ascendant in siciliano lemonade' is the wordplay.
'ascendant' says the letters should be written backwards (in a down clue, going upwards).
'in' indicates the answer is hidden within the clue.
'nolem' can be found hidden inside 'siciliano lemonade'.
'nolem' in reverse letter order is 'MELON'.
(Other definitions for melon that I've seen before include "Large sweet gourd" , "Honeydew fruit" , "Fruit of the gourd family with a hard rind and juicy flesh" , "I'm very seedy" , "Killing" .)