How to create a tomato variety?

The basic principles for creating a tomato variety

To create a new tomato variety, it is necessary to cross-breed two parents, both chosen for their complementary characteristics.

For example, an early, high-yielding variety may be cross-bred with another variety known for its flavour and disease resistance.

The possibilities for cross-breeding are therefore almost infinite, given the number of interesting characteristics found in the many tomato varieties. The selection of these parent varieties is therefore made according to what you expect from their cross.

Please note: cross-breeding is carried out between two stable tomato varieties, never from an F1 hybrid.

Cross-pollination

To hybridise tomatoes, the cross-pollination technique is most often used. Although it is not difficult in itself, the process nevertheless requires great care and patience. In fact, it involves dissecting tomato flowers in order to move, by hand, the pollen from the first parent to the stigma of the second parent.

Hybridisation: prerequisites

Prepare labels showing the names of the two parents to be crossed.

First decide which of the two will be the female parent. As it is the one that will bear the fruit, preferably choose the most vigorous variety.

When should you start hybridising?

To begin, you must wait until both tomato varieties are in flower at the same time. Then, preferably carry out the hybridisation after the garden has enjoyed several consecutive days of fine weather.

How should you proceed?

Select on the female parent a flower at the advanced bud stage, yellow or turning yellow, but still closed, to make sure that it has not already self-pollinated.

Please note that your flower must be alone on the cluster. So remove all the other flowers on the stem to prevent accidental pollen transfer.

Next, proceed as follows:

1. Gently remove the petals from the flower using tweezers.
2. Emasculate the flower by removing its male parts. Take care not to damage the style (the female part) when attempting to remove the stamens (the male parts). Bear in mind that mistakes are not uncommon at this stage. You will probably have to try several times to acquire sufficient dexterity.
3. Once the style is nude, attach the label to the flower’s pedicel, and wait 24 to 36 hours before pollinating it.
4. Once this period has elapsed, take an open flower from the male parent.
5. Still using the tweezers, open its staminal tube lengthways by separating the stamens.
6. Collect the pollen by moving a paintbrush from bottom to top over the inner surface of the stamen.
7. Apply the pollen to the tip of the style of the emasculated flower, called the stigma.

After a few days of patience, if the fruit begins to develop, this means that your cross-breeding has been successful. Otherwise, you will probably have to repeat the process.

Selection year after year to obtain a stable variety

The selection work is only just beginning here. It will take several years before you manage to obtain a tomato variety that produces identical young plants from one spring to the next.

F1 hybrid seeds

Once the pollinated fruit is ripe, harvest it and collect the seeds. Clean the seeds and leave them to dry. Then place them in an envelope and store them away from light until the following spring. You have now obtained home-produced F1 hybrid seeds.

The following year, sow your hybrid tomato seeds, as you would any other tomato variety. However, bear in mind that although the young plants obtained will display the parental characteristics, you will not be able to predict precisely what the result of this combination of characteristics will be.

F2 hybrid seeds

When the hybrid young plant produces fruit in turn, harvest those that best match your expectations. Collect their seeds once again for sowing the following year. The seeds obtained in this way can then be described as F2.

F3 hybrid seeds

The following year, once these F2 seeds have been sown, you will find that each of the young plants obtained displays a wide range of characteristics, with the parents’ genes expressing themselves differently from one plant to another. You must then sort your young plants according to the characteristics initially sought. Therefore, harvest F3 seeds only from the plants that meet your expectations.

F4 hybrid seeds

The same applies to the generation of hybrid tomato plants grown from F3 seeds. Continue your selection, and harvest the seeds that will form the F4 generation.

Stabilisation

It is estimated that after six generations (sometimes ten), it is then possible to obtain a new tomato variety that meets your initial objectives. The line has then stabilised and produces identical young plants from one year to the next.