by Tamara Scully
Hybrid seeds, the result of crossing two different species in the same genus, or different varieties of the same species, are common in farming. Hybridization provides some distinct advantages, combining desirable traits from each parent plant together, such as disease resistance, early or late harvest times, easier harvesting, bigger fruits or better flavors. With hybridization, the first generation offspring is stable and uniform, and genetically identical.
Dr. Jason Cavatorta, president and plant breeder at EarthWork Seeds, had an idea for developing a late blight resistant tomato and was looking for a seed grower. Cavatorta was intrigued, and slightly appalled, when he realized that there was no hybrid tomato seed production being done commercially in the United States. But thanks to Cavatorta’s quest, there is now.
Further exploration led him to the realization that many hybrid tomato seeds, including those that are certified organic, are produced in China and Thailand, although he doesn’t know the exact percentages.
“To produce organic tomato seed, I did not want to go to China,” he said. “There was no one in the United States producing hybrid tomato seeds. So I found Bill.”
That’s Bill Waycott, of Nipomo Native Seeds, who agreed to begin growing tomatoes for seed and develop the hybrid Cavatorta had in mind. Waycott’s 10-acre farm in California had been a prime location for growing tomatoes in the fields. By adding greenhouses for cold-season growing, Waycott prepared to hybridize the plants and produce Cavatorta’s new hybrid.
“It was almost as if we were working in a sterile environment,” Waycott said of his farmland, as tomatoes grown there were almost disease and pest-free, and a large part of the reason he agreed to grow for Cavatorta. “It seems like we can grow tomatoes for seed here.”
Hybridizing the Tomato
Growing in the controlled atmosphere of the greenhouses, however, has caused some issues, as pests and diseases which were not problematic in the fields became a problem with indoor growing. They’ve learned how to utilize organic methods – Waycott comes from a conventional background – to keep the tomatoes clean for seed production, and better control to improve the environment to reduce pest and disease pressures.
Tomato flowers have both male and female parts, as they are monoecious. To prevent self-pollination and make the cross between selected parents, the flowers must be emasculated and then pollinated with the desired pollen. The tomato’s pollen-producing organ encircles the female, requiring that the petals and the pollen cone be removed, and the remaining emasculated flower, with intact pistil and sepals, be exposed.
“We figured out how to extract pollen. We figured out how to emasculate very quickly,” Waycott said.
The results of the genetic crossing of the two parent tomato varieties Cavatorta selected resulted in a very flavorful F1 hybrid, known as Damsel, bred for resistance to late blight disease. But there were some concerns.
“We were getting these big, beautiful fruits, and there were very few seeds in them,” Waycott said. “Turns out that the pollination timing is very, very important.” Ultimately, they tried a variety of pollination schedules to ensure optimal seed production.
“Producing hybrid seeds is very similar to producing seeds in other ways, except for two things. You have to make sure first that parent one does not pollinate itself, and you have to take pollen from parent two” and pollinate parent one, Cavatorta explained. Exactly how this is achieved “depends upon the floral biology of the crop. Crops like tomato are very labor intensive.”
Production costs for the organic hybrid tomato seed, which is now available for growers through Harris Seed, Johnny’s Select Seed, High Mowing Organic Seeds, Territorial Seed Company, Osborne Quality Seeds, Seedway and Garden Trends, runs at about 40 percent of the total gross income costs from the seed, Waycott said.
“It’s not an extremely profitable proposition, but there’s no reason why we can’t produce hybrid seed here in this country,” Waycott said.
Other retailers do sell a Damsel hybrid tomato seed, which Cavatorta is having grown in Costa Rica. This seed is conventional (and less expensive) to meet the needs of growers and seed retailers who prefer that option.
Damsel is a 73-day indeterminate grower, loaded with pink globe-shaped fruits which are resistant to
nematodes and verticillium wilt. Its flavor is said to rival favored heirlooms such as Brandywine. The seed was available for the 2018 growing season.
Because hybrids are “the opposite of open pollinated,” they are excluded from being considered an heirloom vegetable, Cavatorta said. But that doesn’t mean they aren’t flavorful or that they aren’t bred using traditional techniques.
For farmers, having plants which can express numerous desired traits – such as resistance to multiple diseases plus good growing habit and large, tasty fruits – requires introducing some of these traits from each parent and having them reliably expressed in the offspring.
It would be difficult to have one parent exhibit more than a few selected traits. But by selecting cultivars with some of the selected traits in their genome, and selectively breeding them to a plant with the other desired traits in their genome, breeders can pack a larger number of traits into the resulting F1 hybrid progeny.
In open pollination, a heterozygous condition, such as pink flowers, can never be expressed in a stable fashion. In hybridization, however, the selected trait is repeatedly expressed in the F1 generation. And hybrid vigor is a real phenomenon. The F1 hybrids tend to be more robust plants than either parent. Known as heterosis, the exact mechanisms of why this often occurs is not well understood.
Many hybrids are sterile. This trait is beneficial – if something undesirable happened as the result of a cross, that trait would not be able to escape into the population at large. Of course, it is also an economic benefit to those producing the hybrid seeds. Saving non-sterile hybrid seeds won’t result in identical progeny. Although some of the next generation of plants, the F2s, will have traits of the F1 hybrid, they won’t all be identical and there will be a variety of genetic expression.
“If being independent from a seed company is important to you, you probably don’t want to grow a hybrid,” Cavatorta said.
For those promoting a local food system, having a hybrid, certified organic and late blight resistant tomato seed that has been produced in the U.S. – not in another country – is a welcomed development. The irony of a locally-grown tomato being grown from seed produced thousands of miles away was enough to propel the development of the Damsel tomato.
Dr. Jason Cavatorta and Bill Waycott presented at the 2018 Organic Seed Growers Conference in Corvallis, OR.