Tomatoes 101: Guest Blog by Nick Rhodehamel

Jay Gatsby famously says in The Great Gatsby “Can’t repeat the past? Why of course you can!” He’s a larger than life character in a novel, of course, and (of course) he’s wrong anyway. But in good times or bad, most people would turn back the clock if they could. The past often shines more brightly than the future; it’s fixed and known, and though we can’t relive it, we look for reassurance in connections with it.

These connections take many forms. Some people find them in genealogy, some through country dancing, Civil War reenactments, or whatever. I have friends who grow heirloom tomatoes, in part (I believe), to find this connection with the past. They say that heirloom tomatoes have unique qualities (and histories) not found in “modern” tomatoes and that they taste so much better than the grocery store ones. All true, I suppose; I have grown heirloom tomatoes myself, and almost anything that you grow in your own backyard tastes better than what you buy at the grocery store.

Heirloom crops, tomatoes in particular, are very popular. Seed Savers Exchange offers 4713 varieties of tomato heirlooms alone. So called “heirlooms” are traditional varieties or landraces that were originally selected, grown and passed down within families or local regions. There are literally thousands upon thousands of heirloom tomatoes that are largely unique and distinct from one another from around the world.

Tomato was probably domesticated in Mexico from wild Peruvian stock with fruit similar to what we think of as “cherry” tomato. The first record of cultivated tomato comes from the Spanish who found it consumed at the time of the conquest of Mexico in the early 16th century in a limited area from Central America north to Mexico City. When tomato came into cultivation is unknown, but large fruit types had already developed by the time the Spanish appeared in Mexico and possibly before domestication.

The cultivated tomato (Solanum lycopersicum L.) is a member of the Solanaceae family. Solanaceae contains around 3000 species of both the Old and New World origin, many agriculturally important; worth mentioning are eggplant, from China, and tomato, potato, and pepper, from Central and South America. All wild tomatoes, with the exception of one species found on the Galapagos Islands, are native to mainland South America in a region of the Andes that includes parts of Colombia, Ecuador, Peru, Chile and Bolivia.

All forms of cultivated tomato are self-fertile and exclusively inbreeders—barring human intervention or other extraordinary circumstances, individual tomato flowers do not cross pollinate each other. Wild tomato species, in contrast, are both self-fertile and self-infertile. With human aid, most of the wild species (thirteen or seventeen, depending on the classification scheme) can interbreed with cultivated tomato.

Domestication of tomato was brought about by inbreeding and intensive selection for desirable traits, in both Mexico and Europe, but this imposed genetic uniformity on cultivated tomato. And if, indeed, the large-fruit types arose before domestication, those large-fruit plants would certainly have been chosen as the progenitor of cultivated tomato. When these plants, which would have been few and possibly genetically identical, were taken from the Andes to Mexico and then to Europe, tomato was isolated from its source of genetic diversity and what evolutionary biologists call a “genetic bottleneck” resulted. Despite the obvious variety in fruit shape and size, flavor, local adaptation, color and aroma, traditional cultivated tomatoes are genetically impoverished with less than 5% of the genetic potential of their wild cousin. Different varietal names may have been applied to genetically very similar lines. Thus, the proliferation and increase in number of heirlooms over time. The variation that exists in these heirloom tomatoes today is mostly the result of rare spontaneously occurring mutations, such as those that induced the large-fruit types.

Tomato was brought back to Europe by the Spanish and was first consumed in Spain and southern Italy in the mid 16th century (this we know from tomato recipes and shopping lists). By the end of that century, tomato had spread to most of the rest of the Mediterranean region and England and much of the rest of continental Europe. By the 17th century, the Spanish had introduced tomato to their North American outposts in Florida, Texas and California. From there, it gradually found its way to Colonial America, which also received different varieties with the floods of immigrants from Europe. In Colonial America, tomato was eaten rarely in the mid 18th century and commonly by the mid 19th century. Since its arrival in Spain nearly 500 years ago, human selection of desirable and valuable traits in all the regions where tomato was grown has produced an array of varietal types adapted to local climates and incorporated into local cuisines.

While heirloom tomatoes represent a fantastic source of valuable traits, there are distinct advantages to hybrid plants, where the aim is to combine the best characteristics of two inbred lines (one of which is perhaps an heirloom). And in the early part of the 20th century, universities and later private companies began formal tomato hybrid breeding programs. Hybrid tomatoes are tailored specifically for uniformity of such traits as yield, type of desired fruit (canning vs. fresh market), shelf life, disease resistance and climate. Because there’s more work involved in producing hybrid seed, the seed is more expensive. And, unlike inbred heirloom seed, hybrid seed does not breed true and must be replenished each year. But despite the additional expense of hybrid seed, the advantages have led most growers, especially commercial growers, to choose hybrid tomatoes over inbred lines like the heirlooms. The first really successful hybrid tomato was Burpee’s ‘Big Boy’, introduced in 1949 and still popular today.

In contrast to traditional, heirloom tomatoes, wild tomatoes exhibit a tremendous amount of genetic diversity. This is especially true of some of strictly self-incompatible species (obligate outbreeders). Wild tomatoes carry a wealth of genes. Within the next 10 years or so, the complete sequence of the tomato genome will have been determined. And as our knowledge of the structure and function of tomato genes increases, it will become progressively easier for tomato breeders to “design” new cultivars that combine traits of traditional, inbred tomatoes with wild-species traits such as resistances to pathogens, pests, and environmental conditions as well as elevated nutrient content, a current breeding goal.

If like my friends, you enjoy growing heirloom tomatoes (for whatever reason), by all means continue to treat yourself. But don’t overlook the great hybrid tomatoes that are currently on the market. And look to the future because the best tomato varieties are yet to come.

This entry was posted on Tuesday, October 25th, 2011 at 2:02 pm and is filed under Original Posts. You can follow any responses to this entry through the RSS 2.0 feed.
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12 Responses to “Tomatoes 101: Guest Blog by Nick Rhodehamel”

  1. Virginia said:

    What is the best fertilizer for Tomatoes? Last year we used Miracle Grow and got lots of beautiful foliage but not much fruit.
    Thanks

    • Nick said:

      Dear Virginia,

      The best tomatoes I ever grew were on a pony farm. To my knowledge, my landlady never sold any of the ponies. There were about 30 of them; the “girls” were named “Dolly and the “boys” were named “Buster”. My garden was to a side of a barn that no doubt previously had been part of the pasture. A stream ran through a marshy meadow to the side of the barn. The soil was a rich, organic soil that had been made richer by years of rotting pony manure. I also had a good source of composted pony manure.

      That said, what’s your soil like? If you don’t know, I suggest you either get it tested or buy a soil tester. Burpee sells one (Electronic Soil Tester) for under $20. Your local county ag agent should be able to advise you on where to get your soil professionally tested. This will give you a good starting point. Miracle Grow is a good, well-balanced fertilizer and should work well, if you need fertilizer. Lots of foliage and not much fruit sounds like maybe your soil has, relatively, too much nitrogen.

      Here’s a Burpee site called “Top 10 Tomato Growing Solutions”. Maybe, it will be of help.

  2. donna said:

    Could you expand upon “elevated nutrient content”? What is this, exactly? Too much nitrogen, or phosphorus, etc. in the soil? Why? If growers get inferior results from a too-high nutrient level, why not fertilize less? I feel like I’m missing something here.

    Donna

    • Nick said:

      Dear Donna,

      Thanks for asking. People in rich countries (in North America and Europe) have a diet that is various enough that they get most of their nutritional needs from the foods they eat. But in the developing world, many people rely on a few staple foods (rice, corn, wheat, and cassava) that are poor sources of some essential nutrients. Another term for what I’m talking about is “biofortification”, the process of enriching the nutrient content of crops as they grow to provide a “sustainable” solution to malnutrition worldwide.

      One success story is “Golden Rice”. Rice produces b -carotene (or provitamin A, which is processed by the body to vitamin A) in its green tissues but not in the rice grain. When rice is polished, it loses this nutrient (brown rice retains b -carotene, but along with it are fats that oxidize and become rancid, decreasing storage time for brown rice). In Golden Rice, b -carotene is stablely produced in the rice grain itself, giving it a golden or orange color.

      Several other crops have been bred to have increased levels of certain nutrients essential in human diets. Corn with elevated levels of zinc is another example. Species of the Galapagos tomatoes have genes for elevated levels of b -carotene that can be used for improving the provitamin A content in cultivated tomato.

  3. Marci said:

    Great story. I live north of Seattle and our summers are not hot enought(my thinking) for heirloom or large tomatoes. I plant two Sweet 100′s every year and have enought tomatoes until the first frost. I just picked the last of the green ones this morning.

    • Nick said:

      Dear Marcia,

      I know people on the Kitsap Peninsula, and they confirm you observation that your summers are not hot enough for tomatoes in general. I’m glad to hear that the Sweet 100 does well; it’s a great cultivar. Thanks for taking the time to write in.

  4. Emilie Miller said:

    I can’t agree that any non heirloom tomato has any
    excuse for its existence. Tough skin and bland
    taste, while the green striped tomatoes that my local farm grows are well worth the $2 a pound extra they charge. Heirlooms from White Flower Farm were wonderful as well.

    • Nick said:

      Dear Emilie,

      Thanks for taking the time to write in. That’s kind of anthropomorphic and dogmatic thinking, if you ask me. My guess is that you’re eating the wrong hybrids. There are also plenty of good tasting hybrid tomatoes. And there plenty of good reasons to breed hybrid tomatoes (some of which I enumerated in the piece), and those hybrids been widely adopted largely because of those reasons and advantages. No one is forced to eat, buy, or grow hybrid tomatoes. By all means, stick with the heirlooms.

  5. Thank you Nick for the informative article. This year I took my biggest juiciest heirloom tomato and saved the seeds. But I was told to plant seeds from at least two different plants. What do you think of that? Thanks, Cynthia Wylie

    • Nick said:

      Dear Cynthia,

      If the seed you started in the spring was homogeneous, then theoretically, barring something unusual, the seed from ALL fruit (regardless of the plant) should be the same. The Valencia region in Spain is a region where tomato has been cultivated as long as anywhere else (outside Mexico). I know that this is exactly the same procedure that the traditional farmers practice there. It is region of great tomato diversity.

  6. Steve McNew said:

    What I’m looking for is a Really Resistant line, to the F. wilt that infests my ground. Am currently working on a water tube boiler, to steam the garden areas. Do you guys have any experience with such things? Thanks, Steve steve.mcnew@sinclair.edu

    • Nick said:

      Hi Steve,

      Since you’re about to steam your soil, my guess is that you’re aware of or have tried the things I’m about to suggest. Planting disease resistant tomatoes is the first and best approach. Are you sure that what you have is Fusarium wilt? Disease symptoms are pretty similar to those caused by Verticillium, which also persists in the soil. Mostly resistance to both Fusarium wilt and Verticillium wilt is incorporated into resistant cultivars, but not always. Check out this Ohio State factsheet on Fusarium and Verticillium wilts in Solanaceous crops (http://ohioline.osu.edu/hyg-fact/3000/3122.html). It may have some ideas you haven’t considered. Good luck.

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