Struggle in variety (6)
I believe the answer is:
strain
I believe this is a double definition.
'struggle' is the first definition.
(I've seen this before)
'variety' is the second definition.
('strain' can be a synonym of 'variety')
'in' is the link.
(Other definitions for strain that I've seen before include "Pass through a sieve" , "'Stress, tension (6)'" , "Tension - stock" , "Strive; ancestry" , "Difficulty that causes tension" .)