Gardener mad about one pineapple specialist? (9)
I believe the answer is:
grenadier
'pineapple specialist?' is the definition.
(pineapple can mean a grenade)
'gardener mad about one' is the wordplay.
'mad' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'one' becomes 'I' (Roman numeral).
'gardener' with letters rearranged gives 'grenader'.
'grenader' placed around 'i' is 'GRENADIER'.
(Other definitions for grenadier that I've seen before include "Soldier - in red gear (anag)" , "A household infantryman" , "historical bomber" , "Infantryman - in red gear (anag)" , "Soldier; fish; bird" .)