Experimenting with a new tomato variety
September 3, 2014
Author: Neighborhood Farm Initiative
Category: General News
This year we were delighted to have Lori Knepp, an avid gardener who also participated in our Oral History Project, and has donated multiple seedlings to us over the years, about her tomato experiment. Check out her interview below and join us during any of our open hours to look at her tomato experiment!
1) How long have you been gardening?
I’ve been gardening since I was 5 years old—so that makes it 45 years of gardening. I have been growing vegetables the entire time. On the maternal side of my family, the women have been gardeners for past several generations.
2) When and why did you get started growing your own seedlings?
I started growing my own seedlings about 10 years ago. There were so many great varieties advertised in the seed catalogs that arrive in the middle of winter that I decided that I wanted to grow my own tomatoes. I was really interested in heirloom tomatoes from the start.
3) What are your favorite seedlings to grow?
I love growing tomatoes. I grew 33 varieties of heirloom tomatoes this past year. I always grow Purple Cherokee, Hillbilly Potato Leaf, Japanese Black Trifele, Black Krim, Black from Tula, and a currant-sized tomato called Bird (I received Bird Tomato seeds from a seed swap several years ago). I love the purple/ black varieties of tomatoes. They are a beautiful color and have a lovely complexity of flavors. Some new favorite tomatoes from this year are: Paul Robeson (a mahogany tomato that is very beautiful), Rose d’Eauze (a rare French pink tomato with a big, old-fashioned, tomato taste), Vintage Wine (a pink and yellow striped tomato with an acidic pop), and Surender’s Indian Curry (a small curry tomato with a rich complex taste when cooked into a sauce).
In addition to the tomatoes I start basil, parsley, and other herbs from seed, as well as leeks, peppers, eggplants, kale, and cabbage. I set up a bank of grow lights on chains in my basement and start planting seeds in late winter/early spring. It is quite a production. My favorite seedlings to watch emerge are the . The initial leaves are extremely miniature strawberry leaves. They are sweet little plants.
4) How does someone create a new variety of tomato?
New varieties of tomatoes can occur through intentional cross pollination, natural cross-pollination (wind, insects, birds), and by a mutation in the plant that can produce a tomato with different characteristics than the tomatoes of the host plant—this is called a sport or mutant.
Cross pollination will not initially result in a stable or true strain of tomatoes and the seeds from a cross-pollinated flower can create plants with a wide variety of traits from the two parent plants. Tomatoes that are hybridized by the seed companies are also cross-pollinated and will not produce “true” if you plant the seeds from the tomato. This practice of commercial hybridization cancels out varieties that are unique, but might have an undesirable trait as decided by the commercial seed companies. I am concerned about this reduction in our seed heritage and want to support the continued growing of heirlooms. I joined Seed Savers Exchange out of Decorah, Iowa this past year. It is a fantastic organization that promotes seed saving and preservation and keeps our seed heritage robust and strong.
5) What’s the difference between cross-pollination and a new sport/mutant (variety)?
Cross-pollination occurs at the seed level — genetic material is exchanged between host flower and pollen. The creation of a sport or mutant occurs when there is a mutation of the genetic material in the plant and the host plant, itself, is responsible for the mutation and change in fruit characteristics without the genetic material from the outside pollen.
6) How did you stumble upon your potential new tomato variety?
Last October 2013, I was collecting some of the last tomatoes from my garden to make tomato sauce. I had collected several red and purple/black tomatoes. When I cut into one of the purple/black tomatoes, I discovered that this one tomato was unique and not like anything I had planted or harvested that year—it was purple/black on the outside and green, yellow, and red inside. I saw that it was something special and saved every seed from this tomato. The tomato was both beautiful and delicious with some of the flavor profiles of green and yellow tomatoes—lower acidity, and milder, slightly citrusy flavor.
7) Tell us about how you’re testing out your tomatoes—how did you start and how are you recording?
I contacted Seed Savers Exchange to ask them about this mystery tomato and was informed that it was either cross pollination or a sport/mutant. I was advised to grow twelve plants from the seeds I collected from my original mystery tomato. If the tomatoes from these twelve plants were like the original tomato–at a ratio of 3:1 – then the original tomato was probably a mutant or sport. Mutant/sports are considered a unique, new, variety of tomato that can be named. If the tomatoes produced by these plants had a variety of characteristics and did not look like one another, then it was fairly certain the variety is a result of cross-pollination.
Neighborhood Farm Initiative at Mamie D. Lee Community Garden provided me with a plot to grow the twelve tomatoes. My initial findings were confusing. There were quite a lot of variety in the tomatoes that I had grown, however there were also some tomatoes similar to my original tomato, but not quite as purple/black red on the outside. I have again consulted with Seed Savers Exchange and also talked with Neil Hoffman who gardens at Mamie D. Lee both who know much more about the science and genetics of plants than I do. Since the original October 2013 mystery tomato was unique and the only one of its kind produced on the original plant, we think that it was probably a mutant/sport. We also think that the flower that produced this unique tomato was probably also cross-pollinated either by the other flowers on the parent plant or other tomato plants in the garden. This might explain why I am getting similar tomatoes to my original mystery tomato as well as two other types of tomatoes that are different from the original tomato. So…it seems that I might have a mutant/sport that was also cross pollinated. I am now re-looking at all of the tomatoes coming off the twelve plants to see if they are producing anything closer to my original mystery tomato.
Here is Neil’s scientific explanation which is really interesting:
To explain the observation that seed from the sport fruit produced more sport fruit, and two different looking red fruit, there are a number of explanations. The simplest possibility is that the sport mutation occurred in a change in a single recessive gene. In tomato, there are normally two copies of each gene-one is derived from the mother plant (ovule) and the other from the pollen. Recessive means that both genes need to have the mutation in order to see the “sport” phenotype. when both copies of the gene are the same, it is called homozygous. When the copies are different, it is called heterozygous.
If this idea is correct, the ovary of “sport” fruit would have two copies of the mutation. The ovary is the part of the flower that matures into the fruit. According to this hypothesis, the appearance of the fruit in the fall is from a sport mutation that results in both genes of the ovary having the “sport” mutation.
Cros-spollination can explain why you observed different phenotypes from the seeds of the sport fruit.
The ovary of the flower that develops into the fruit contains ovules. The seed is derived of one gene from the mother plant (ovule) and one gene from the father plant (pollen). The seed could be pollinated from the same flower that develops into the sport fruit. If this pollen also had the sport mutation (because it came from the same flower), when it fertilized a sport ovule it would produce a seed that has both sport genes. In such a case the seed would grow into a plant that produced the green fruit.
The ovule (with the sport gene) might also be pollinated from pollen from another flower from the same plant (that is not the sport) or from pollen from another plant (also not the sport). The resulting seeds would then be comprised of a sport ovule fertilized by a non sport pollen. These seeds would produce tomatoes that yield red tomatoes in the heterozygous state, if the “sport” mutation is recessive.
How to explain the two different red phenotypes. One possibility is that the two phenotypes represent cross pollinations to flowers from the same plant versus cross-pollinations to different plants (a completely different genetic background). Note that the flowers producing red flowers from the same plant are expected to be genetically very similar to the “sport” flower producing green tomatoes. When these flowers cross pollinate, very little new genetic diversity will be introduced. When a cross pollination occurs between the sport flower and a flower from a different red tomato variety, most genes in the resulting seed will now be heterozygous. Consequently it is possible that those two phenotypes represent cross pollinations with flowers from the same plant (more genes overall are homozygous) or pollinations from flowers of a nearby plant (more genes overall are heterozygous).
If this hypothesis is correct, we would expect the seeds from the green fruit to always produce plants bearing green fruit and the seeds from the red fruit to produce 3 plants bearing red fruit for every one plant bearing green fruit. The red fruited phenotype may be somewhat complex because it is likely the result of multiple genes that will be segregating in subsequent generations. In order to figure this out you need to avoid any cross pollination. It might be helpful to discuss with a tomato breeder how they eliminate cross pollination. Perhaps they bag flowers before pollen is shed and make sure this is some distance between plants.
8) What advice would you tell someone who wants to try the same test?
There is quite a bit of information on the internet on how to create new varieties of tomatoes through cross pollination. It takes a lot of patience. This is a process that deals with the plants on a different and unique level than the cultivation involved in “just vegetable gardening.” Creating a new variety involves a commitment to seeing the seeds and plants through several generations of testing. I think it can be a challenge for the home gardener because most articles that I have read recommend that tomato varieties be separated by 100 feet with different crops in between to prevent unwanted cross-pollination or the individual flowers need to be bagged using fine mesh bags to isolate the flowers once they have been cross-pollinated. You won’t see results of your cross-pollination until you plant the seeds come from the tomato formed from that flower the following year.
9) If you do create a new variety, what do you plan on naming it?
I am still trying to figure out if there is any way to get back to the original mutant/sport that appeared last October. I have had fun talking with friends about possible names if it does turn out to be a mutant/sport. First, I want to identify it with the neighborhood where I live and grew the tomato—Brookland. We also thought that since the tomato was not produced in the typical way—with typical tomato reproduction—that it might be called Brookland’s Love Child or Brookland’s Bastard. David Quick who produced the Oral History of DC Gardeners has offered Brookland’s Cardinal Sin which is my favorite name right now. I’ll see if I can figure out how to get back to the mutant/sport and if I can, then I guess we will have a christening.