Fruit Tongan farms regularly served up (5)
I believe the answer is:
mango
'fruit' is the definition.
(type of fruit)
'tongan farms regularly served up' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'served up' is a reversal indicator (in a down clue, going upwards).
'tongan'+'farms'='tonganfarms'
The alternate letters of 'tonganfarms' are 'ognam'.
'ognam' reversed gives 'MANGO'.
(Other definitions for mango that I've seen before include "Asian fruit" , "Fleshy tropical fruit" , "Once exotic fruit" , "Yellow-fleshed fruit" , "fruit tree" .)