F1

F1 stands for “first filial generation” - the Latin filius means son or offspring. An F1 hybrid is the first-generation offspring of a cross between two distinct inbred parent lines. The designation appears on seed packets and in catalogs to indicate that the variety was produced by intentional hybridization rather than open pollination.

The Genetics

When two genetically distinct lines are crossed, the F1 offspring inherit one copy of every gene from each parent - they’re heterozygous at every position where the parents differ. This genetic diversity often produces heterosis (hybrid vigor): plants that grow more vigorously, yield more, or show greater disease resistance than either parent line alone.

The specific traits that appear in F1 plants - which characteristics “win” - depend on dominance relationships between genes and which traits the breeder selected for in the parent lines. Breeders cross-test many different parent line combinations before releasing a commercial F1 variety.

Why F1 Seed Doesn’t Breed True

If you save seed from an F1 plant and grow it out, the offspring (F2 generation) will segregate. Each F2 plant gets a random combination of the original two parents’ genetics. Some F2 plants will resemble the F1 parent somewhat. Many will not. The uniform, vigorous characteristics of the F1 disappear in the F2 because those characteristics depended on that specific heterozygous genetic combination.

This is why F1 seed requires annual purchase. A seed company maintains the two inbred parent lines in separate plots, crosses them in a controlled way each year, and sells the resulting F1 seed. The breeding work that produces the F1 is proprietary.

F1 vs. F2 vs. Open-Pollinated

• F1: first-generation cross, heterozygous, uniform, vigorous, doesn’t breed true
• F2: second generation from selfing or crossing F1 plants, highly variable
• Open-pollinated: long-stabilized, breeds true, seeds saveable

Some plant breeders deliberately sell F2 seed of interesting crosses as “breeding projects” - you get variable offspring and can select and stabilize traits you like over several generations. This is the process by which new open-pollinated varieties are eventually developed from hybrid crosses.

Practical Implications

For most home gardeners, the F1 designation signals:

• Good uniformity and disease resistance
• No point in saving seed
• Annual seed cost is the trade-off for genetic consistency

The cost difference between F1 and open-pollinated seed varies by crop. F1 broccoli and cabbage seed is expensive because controlled pollination in these crops requires significant labor. F1 tomato seed is moderately more expensive than OP seed, but the cost per plant (a few cents) is trivial against a full season of production.