North Dakota produced certified seed is limited to seven years of reproduction in the field, generations 0-5 and the Certified Class. Generation 0 seed is produced from tissue-culture derived, pre-nuclear seed stocks. Subsequent generations advance by each field year.

Generation 5 seed is the last year eligible for recertification. The Certified Class is the progeny of Generation 5, and used only for commercial planting purposes. Seed is downgraded (advanced in generation) if it does not meet tolerances for disease or varietal purity for the generation applied.