Flavour is the main issue (6)
I believe the answer is:
season
'flavour' is the definition.
('season' can be a synonym of 'flavour')
'the main issue' is the wordplay.
'the main' becomes 'sea' ('sea' can be a synonym of 'main').
'issue' becomes 'son' (issue can mean someone's offspring).
'sea'+'son'='SEASON'
'is' acts as a link.
(Other definitions for season that I've seen before include "eg Winter" , "Time of 9" , "instruction in recipe" , "make things palatable" , "Add flavour at a certain time of year" .)