F1 seeds

F1 hybrids

Gardeners often wonder why hybrid seeds are relatively costly and question whether their performance justifies the price. Another common question is whether seed saved from F1 hybrids is worth keeping.

Quick facts

Scientific name F1 hybrids
Plants affected Many vegetables, bedding and ornamental plants
Main causes Man-made hybridising of plants

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Introduction

Plant breeders seek to make better plants. They do this by controlling how plants interbreed or ‘cross’. By crossing selected plants with different but desirable features, they produce a plant that has the best features of both parents. This is then crossed further to produce a stable plant whose seeds produce plants that are true to type.

An example might be crossing a tomato with large orange fruits with one that has small very sweet red fruits in order to produce a tomato with small, very sweet orange fruits.

There are several techniques used to cross plants (some of which are listed below), but producing F1 hybrids is one of the commonest and most effective methods.

What are F1 hybrids?

F1 hybrids, which are largely annual and vegetable cultivars, are produced by crossing two stable seed lines (called inbred lines) that give rise to especially uniform progeny that possess good vigour, yield and other properties. Tomato ‘Cristal’ F1 and sunflower ‘Harlequin’ F1 are examples of F1 hybrids. It will say on the seed packet if the variety is F1

Pros and cons of buying F1 seed

  • Greater uniformity of flowering, stature, yield and maturity period. Although uniformity is usually more valuable to commercial growers, hybrids usually offer worthwhile advantages to home gardeners over other forms of seeds
  • Greater size and vigour of flowers or produce due to the phenomenon of hybrid vigour (heterosis). Hybrids are therefore more robust and better able to overcome adverse growing conditions
  • Plant breeders benefit because they control the inbred lines. Therefore the hybrids they breed cannot be grown by other seed companies who lack the parent lines. Although this keeps costs of F1 hybrid seed high, it is an incentive for breeders to produce new and better cultivars, to the benefit of all growers
  • Seeds saved from F1 hybrid plants will not produce plants that are true to the parent type
  • F1 hybrid seed is expensive as it has to be recreated by crossing the parent inbred lines again. Self pollination of the parent inbred lines leads to poor quality plants called ‘selfs’. Preventing selfs is complicated and costly which also contributes to the expense of F1 hybrid seed
  • Due to the cost of maintaining the inbred lines, quite a lot of seed has to be sold for a hybrid to be commercially viable. For this reason hybrids are often only offered for a few years before coming off the market leaving gardeners to seek a replacement for favourite cultivars

Understanding inbred lines

The inbred lines are the critical part of F1 hybrid production accounting for much of the cost and complexity of producing F1 hybrid seed. Inbreeding is allowing closely related plants to set seed. This, after several generations, leads to a population of very similar plants. Inbred lines lack vigour and perform poorly and are difficult and expensive to maintain.

Perhaps surprisingly then, when two inbred lines are crossed, the first generation (F1) is uniform and vigorous due to heterosis. Hybrid vigour is not fully understood but crosses between certain lines will produce especially vigorous offspring. Breeders of F1 hybrids aim to use parent lines whose progeny show particularly strong hybrid vigour.

Some plants, lettuce for example, are intolerant of inbreeding and self-pollination. They suffer from ‘inbreeding depression’, causing a serious loss of vigour, fertility and stature. It is not possible to raise F1 hybrids for species that are not readily inbred. Wild plants tend to be intolerant of inbreeding, but the process of domestication has led to populations that can tolerate inbreeding and therefore hybrids are feasible for many crops.

Some alternatives to F1 hybrids

F2 Hybrids
These offspring of F1 hybrids are variable but for some crops this is desirable. F2 hybrids are relatively inexpensive. Pansy ‘Joker Series’ AGM are a widely offered F2 hybrid where the variation compared to F1 hybrids is not considered to be a drawback and whose seed is significantly less expensive than F1 hybrid seed.

Open-pollinated seeds
When a group of selected plants are grown together and allowed to freely pollinate each other, the seed is said to be open-pollinated. Before the advent of hybrids all seeds were open-pollinated. Open-pollinated seeds are the only option for plants that cannot be easily inbred – lettuces, peas and runner beans for example.

Open-pollinated seed is available for all crops offered as hybrids, but is usually significantly less uniform, vigorous and productive. Open-pollinated seed is relatively inexpensive and can often be readily collected by home gardeners. However, seeds harvested from garden plants will not always come true to their parent, particularly if there is a related plant nearby with which it could have hybridised.

Other hybrids usually sold as plants rather than seed:

Specific hybrids
Theses are plants produced by crossing different species, for example Viburnum farreri and V. grandiflorum. The resulting offspring are indicated by an × symbol before the species name. This can occur in the wild but more are common in cultivation, as in Viburnum × bodnantense.

Generic hybrids
These are plants derived from crosses between two or more genera, such as Heuchera and Tiarella. The resulting offspring are indicated by an × symbol before the composite genus name, as in × Heucherella ‘Stoplight’.

What Are F1 Plants & Seeds: How & Why of F1 Hybrids

An F1 hybrid is simply the result of breeding two different strains of a variety to produce a third variety. The term ‘F1’ just stands for Filial 1 or ‘first children’.

Why produce F1 Hybrid Seeds?

This simplistic example should make it clear as to the why and how of F1 hybrids.

Imagine you’re a plant breeder and you’ve developed a new variety of tomato ideal for growing in the British summer. It’s taken years of patient seed selection and is now stable, breeding true generation to generation.

Over in the greenhouse you’ve another variety of tomato. It’s taken years to develop and is now stable. Its big advantage is that it is blight resistant. Useless for growing outdoors but otherwise fine.

These stable plant varieties are known as pure lines because they breed true without lots of variants growing, they are pure. This is important to consistent results from hybridisation.

You then hand-pollinate to cross your two pure lines together and produce seed. With luck you now have a plant that is great to grow outdoors and is blight resistant. This first cross is the F1 Hybrid.

Producing F1 Hybrid Seeds

To produce a supply of these F1 seeds the breeder has to maintain two pure true varieties as well as a stock of breeding plants that are usually hand pollinated.

This is clearly far more expensive than producing non-hybrids.

Hybrid Vigour

Often with F1 hybrids you have a bonus in that this cross will grow really well. It’s a phenomenon that is well known called hybrid vigour. This only happens in the first cross. If you use the F1 hybrid to produce a second generation – which is known as an F2 – you lose this benefit.

Producing Seed from F1 Hybrids

So, at the end of the season we save some of the seeds from our blight-resistant, outdoor tomato and next year grow them. What a disappointment! Some will be blight-resistant, some great for outdoors growing but not both. None will be as vigorous and productive as their parent.

An F1 is not a ‘pure line’ and stable. It contains genes from both parents and how these will combine in the offspring is a matter of random chance.

There is no benefit for the home grower in saving seed from F1 Hybrids.

Benefits of F1 Hybrid Seeds

  • The hybrid combines the best of both parents and excels both of them
  • The hybrid will be stable and ‘do what it says on the tin’
  • The hybrid will most probably be a vigorous and productive plant.
  • The breeder knows he has an ongoing market for his seed in that people can’t just buy a packet and then produce their own in subsequent years.

Drawbacks of F1 Hybrid Seeds

  • The seed is more expensive. Either the packet price is higher or the quantity in the pack reduced but they will cost more.
  • You cannot seed save and produce your own plants. You are forced into buying seed when it runs out.
  • If the breeder stops production for any reason you are stuck. Once the seed stock is gone, it is gone for good unless you know the parentage and have stocks of the parent plants’ pure lines.

Genetic Modification for F1 Hybrids

To bust a myth I’ve come across – F1 hybrids are not genetically modified. It is a completely natural plant developed and bred conventionally.

F1 Hybrids are Just a Money Maker

I’ve read that hybrids are really just a way for seed companies to stop us producing our own seed and boosting their profits. A dark conspiracy by the corporate gnomes.

It’s true the seed producers make money from the hybrids which they need to cover the cost of development and production. But people will only buy hybrids that offer distinct advantages over open pollinated varieties that they can grow for free.