The concept of “true to seed” describes a plant that, when grown from seed, will produce offspring genetically identical to the parent plant. Gardeners who wish to save seeds from their harvest rely on this characteristic to ensure the consistency of their crop. Understanding which varieties exhibit this stability is important for anyone planning to harvest and replant seeds. Whether a tomato is true to seed depends entirely on its specific genetic makeup and how it was bred.
Understanding Open-Pollinated and Hybrid Varieties
Tomato varieties fall into two main categories that determine their seed stability. Open-pollinated (OP) varieties are genetically stable, meaning their seeds will grow plants that are true to the parent type, provided they are not cross-pollinated by another variety. This stability results from consistent self-pollination over many generations. Heirloom tomatoes are a type of OP variety passed down through generations, often for at least 50 years, due to desirable traits like flavor or regional adaptation.
Hybrid tomatoes, specifically F1 hybrids, are created through a controlled cross between two distinct parent lines. The resulting seeds are the first filial generation (F1), which often exhibit superior traits like disease resistance or higher yield, a phenomenon known as hybrid vigor. Unlike OP types, these F1 seeds are not genetically stable and will not reproduce a plant with the same characteristics if their seeds are saved and replanted.
Why F1 Hybrid Seeds Do Not Reproduce True to Type
F1 hybrid seeds fail to reproduce true to type because of their heterozygous genetic composition. Each F1 plant carries a mix of genetic instructions from two genetically different, pure-breeding parent lines. While the first generation (F1) is uniform, this uniformity is only temporary.
When an F1 hybrid plant self-pollinates, it creates the next generation, called the F2 generation. The genetic material begins to segregate, meaning the mixed traits from the two original grandparents are reshuffled and expressed in unpredictable combinations. The resulting F2 plants display a wide range of characteristics, often reverting to various ancestral traits. This loss of uniformity makes the F2 generation inconsistent in important qualities like fruit size, flavor, and disease resistance.
Maintaining Genetic Purity When Saving Tomato Seeds
To ensure saved tomato seeds grow true to the parent plant, gardeners must select an open-pollinated variety. The selection process begins by choosing seeds from the best, most characteristic fruits on the healthiest plants. Selecting seeds from multiple healthy fruits across several plants of the same variety helps maintain a good level of genetic diversity.
While tomatoes primarily self-pollinate, cross-pollination by insects can occasionally occur. To maintain genetic purity when growing multiple varieties, the seed-saving plant should be isolated from other tomato varieties by a small distance, though a separation of 2 to 10 feet is often sufficient for a home garden. The final step involves fermentation, where the seeds and pulp sit for three to five days. This process breaks down the gelatinous coating (aril), which contains a germination inhibitor, and helps eliminate seed-borne diseases, increasing viability and germination rates.