Gardeners often wonder if they can save seeds from their harvest and plant them the following season to get the exact same fruit. This practice hinges on a plant’s ability to “grow true to seed,” meaning the offspring will be a precise replica of the parent plant. Understanding the genetics behind this fidelity is fundamental for successful seed saving. Whether a tomato will grow true depends entirely on the specific variety grown.
Defining Genetic Consistency
For a tomato plant to grow true to seed, it must possess a high degree of genetic stability, known as homozygosity. Homozygosity means the plant carries identical gene variants from both parent lines for a specific trait. Since the majority of tomato flowers are self-pollinating, they naturally inbreed over generations, which promotes this genetic uniformity.
When a plant reaches this state of genetic fixity, the seeds it produces are essentially exact genetic copies of the parent, provided the plant pollinates itself. Plant breeders work over many seasons, sometimes eight to ten generations, to select for the best traits until the variety becomes stable and reliably breeds true. This process ensures that desired characteristics, such as fruit size or plant habit, are genetically fixed and will not vary in the next generation.
The Crucial Distinction: Open-Pollinated Versus Hybrid Varieties
The ability of a tomato to grow true to seed depends entirely on whether it is an open-pollinated or a hybrid variety. Open-pollinated varieties, which include heirlooms, achieve genetic consistency through repeated self-pollination over many generations. This process leads to the homozygosity necessary for genetic stability, meaning saved seed will reliably produce a plant identical to the parent.
Open-pollinated tomatoes are valued because their seeds can be saved and shared indefinitely without trait loss. Heirloom varieties are simply open-pollinated types with a long history of being passed down through generations, attesting to their established genetic stability.
Hybrid tomatoes, labeled as F1 hybrids, are developed through an intentional cross between two genetically distinct, inbred parent lines. This cross is performed by breeders to combine desirable traits from both parents, such as disease resistance and high yield. The resulting F1 seed is genetically uniform, meaning every plant in that first generation will look and perform the same way.
The F1 generation often benefits from hybrid vigor, or heterosis, resulting in stronger plants, higher yields, and more uniform fruit. This vigor is a product of their temporary genetic diversity, known as heterozygosity, where they carry different gene variants for the same trait. This genetic makeup is why F1 seeds are not stable for saving, and the parental lines must be maintained and crossed every season to produce new F1 seed for sale.
What Happens When Hybrid Seeds Are Planted
When a gardener saves and plants the seeds from an F1 hybrid tomato, they are planting the F2, or second filial, generation. This generation is genetically unstable because the hybrid plant carries a mix of different alleles from its two distinct parent lines. When the F1 plant self-pollinates, these gene variants segregate and recombine randomly in the offspring.
The result is extreme genetic segregation in the F2 generation, meaning the plants will display a wide and unpredictable range of traits. Instead of getting a duplicate of the high-yielding F1 plant, the gardener may see plants that resemble one of the original, less desirable grandparents, or entirely new combinations. For example, the fruit might revert to a smaller size, a different color, or lose the disease resistance. This variability is why F1 hybrids cannot be reliably saved for seed.
Practical Steps for Successful Seed Saving
For gardeners who wish to save seeds that grow true, the first step is selecting exclusively open-pollinated or heirloom varieties. To maintain genetic purity, isolation is necessary, even though tomatoes are predominantly self-pollinating. Protecting the plant from unintended cross-pollination by insects is accomplished by maintaining a distance, often recommended to be at least 10 to 35 feet between different varieties.
Only save seeds from the healthiest, most vigorous plants that produce the best fruits. Tomato seeds require a specific cleaning process called fermentation to prepare them for storage. The seeds and their surrounding gel sac are scooped into a container and allowed to ferment for two to three days. This process dissolves the germination-inhibiting gel around the seed and eliminates many seed-borne diseases. After fermentation, the viable seeds will sink, allowing the gardener to rinse away the floating pulp and non-viable seeds before drying them.