When plants reproduce, as with animals, the offspring display traits provided by their parents' genes, in this case male pollen and female ovules. The first cross of two pure lines of plants such as tomatoes results in an F1, or first filial, plant, while the second-generation cross is called an F2. In biology, the term filial denotes a generation after a parent.
F1 tomatoes result when two inbred tomato plants, such as a beefsteak and a Roma, are crossed. The offspring will be identical to each other and display characteristics of whatever gene is dominant for fruit color, size, juiciness or lack thereof, and type of leaf. If the F1 plants are then crossed with each other, F2 plants result and can display almost any characteristics, including recessive genes not apparent in the F1 plants.
Because hybrids result from the crossing of two different pure lines. the first generation (F1) contains exactly the same two sets of genes. Because the F2's contain a random mixture of genes, the plants may have desirable and undesirable characteristics, according to Joran Viers of New Mexico's Bernalillo County Cooperative Extension Service.
Seed saved from hybrid tomatoes creates unpredictable F2 plants, with hundreds and possibly thousands of potential varieties. Thus customers must buy new hybrid seed each year, a benefit to seed producers. Some tomato growers prefer open-pollinated (non-hybrid) tomatoes, which they can save their own seeds from season to season.
F2 tomatoes are on the road to becoming new and valuable strains of open-pollinated, non-hybrid tomatoes, but this may require three to 10 generations, according to heirloom tomato expert Carolyn J. Male. The offspring of the initial hybrid tomato needs to be grown for multiple generations until its genetic components become consistent and it is no longer a hybrid. Tomato grower Tom Wagner of Washington state created tomato varieties Green Grape, Green Zebra and Banana Legs by this process, she notes.
"Because F1 plants contain genes from two different lines, their progeny (F2 generation) will behave more like out-crossed plants," notes Rhoda Burrows of the South Dakota Extension. She states that F2's contain a random assortment of the genes from either of the F1 parents--the desired ones along with the bad ones. Some plants may look like the F1 hybrids, but many look and grow quite differently, she notes.