Prefixes:
* Agro- (relating to agriculture): Agro-grain (referring to grains used in agriculture)
* Cere- (relating to grain): Cere-grain (an alternative term for grain)
* Gran- (relating to grain): Gran-seed (a type of grain seed)
Suffixes:
* -ary: Granary (a storehouse for grain)
* -ier: Grainer (a person who works with grain)
* -ing: Graining (the process of imitating the appearance of wood grain)
* -less: Grainless (lacking grain)
It's worth noting that these are just some examples, and the specific prefix or suffix that is most appropriate will depend on the specific context.