Producing the perfect tomato

Image by regan76 (CC BY 2.0)

Image by regan76 via Flickr (CC BY 2.0)

This summer, I’ve been growing some vegetables in my garden. As a novice gardener, I selected some plants to grow on the basis of what is “easy to grow” rather than any other concern. Fortunately for me, one of my favourite foods happens to be the tomato, and tomato plants (Solanum lycopersicum) are very easy to grow even in small gardens like mine.

For culinary purposes, we generally treat the tomato as a vegetable, but it is in fact a fruit. The tomato plant comes from the Andes in South America where it grows as a vine (1). It is not certain when the plant was first cultivated but it was already being grown in Southern Mexico by 500 BC. At this time, the fruits were about the same size as cherry tomatoes and likely to be yellow in colour.

Today, tomato plants are grown across the world and produce fruits of various sizes and in a range of colours from yellow to red. The spread of tomatoes around the globe started in the early 1500s when the Spanish conquered South America (1). The Spanish took tomatoes to back to their colonies in the Caribbean and to Europe. Tomatoes quickly proved to be a hit in Southern Europe and were soon incorporated into the local cuisines. However, it took longer for tomatoes to catch on in Britain because, at first, many people thought that the fruits were poisonous due to their resemblance to the fruits of deadly nightshade, which belongs to the same plant family as tomato and potato (Solanaceae). Eventually, the British realised what they had been missing, and by the mid 1700s, S. lycopersicum was grown widely in Britain and in North America (1).

While writing this article, a fellow train passenger asked me “why do the tomatoes from my garden taste better than ones from the supermarket?” The answer is that the flavour of the fruit is influenced by when it is picked. Ideally, a tomato should stay on the vine until it ripens as this maximises its sweetness. However, soon after they ripen they become too soft and go off (over-ripen). This is not a problem if you are growing tomatoes in your garden, but for commercial growers that need to transport large quantities of tomatoes over long distances this is a big issue. As a result, most commercially grown tomatoes are picked and transported when they are still green (not ripe). When the tomatoes near their destination they are treated with a plant hormone called ethylene, which causes them to ripen. This enables consumers in many countries to eat fresh tomatoes all year round, but unfortunately also means that the fruits are less sweet than they could be.

The demand for sweeter tomatoes has led to tomatoes that are ripened “on the vine” becoming increasingly popular “premium” products. These tomatoes are removed from the plant along with a section of the vine so that the tomatoes can still gain flavour and sweetness from it.

Another possible solution is to develop tomato varieties whose fruits have a longer shelf life once they ripen. In the 1990s, researchers in the US developed a genetically modified tomato variety – called Flavr Savr – that was missing an enzyme that normally causes the fruit to over-ripen (2). This meant that the fruits could be left on the tomato plants until they ripened and then transported long distances without compromising their shelf life. The tomatoes were initially popular but the company the developed them ran into financial difficulties so the tomatoes ceased to be produced in 1997. A similar tomato variety was also developed in Europe and products containing these tomatoes were sold in UK shops until a scare over the safety of GM food in 1998 led to public opposition and the supermarkets withdrew the products (2).

More recently, a group of UK researchers have developed another variety of tomato that also have a longer shelf life than normal tomatoes (3). These tomatoes have been genetically modified to contain genes that increase the production of pigments called anthocyanins so that the skin and flesh of the tomatoes are deep purple. The researchers were interested in these anthocyanins because they have been reported to have health benefits and, indeed, the purple tomatoes increased the life expectancy of cancer prone mice. However, the researchers also noticed that the anthocyanins slowed down the over-ripening process and made the tomatoes less susceptible to a fungal disease (3). Purple tomatoes are now being produced in Canada so that the tomato juice can be used in further experiments to assess the potential health benefits (4). It is possible that the tomatoes might be licenced for commercial production in some countries within the next few years.

Note: Apologies for the long gap since my previous post. Over the summer I’ve experienced a spell of “writer’s block” and so I decided to give myself a “blogging” break. I spent much of the summer reading fiction books and gardening and now feel it’s the right time to get back into a more regular blogging routine. I’m aiming to post every other week for the next few months. As ever, I’m always interested to hear from anyone who would like to write a guest post.

References:

  1. Wikipedia: Tomato https://en.wikipedia.org/wiki/Tomato (retrieved 14/09/15)
  2. Wikipedia: Flav Savr https://en.wikipedia.org/wiki/Flavr_Savr (retrieved 14/09/15)
  3. Zhang et al. (2013) Anthocyanins Double the Shelf Life of Tomatoes by Delaying Overripening and Reducing Susceptibility to Gray Mold http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3688073/
  4. BBC News “Genetically-modified purple tomatoes heading for shops” by David Shukman, Jan 2014 http://www.bbc.co.uk/news/science-environment-25885756 (retrieved 14/09/15)
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9 thoughts on “Producing the perfect tomato

  1. Excellent post! I might add that “Indigo Rose” is an open pollinated purple variety we have here in the states. Oregon State University bred it from wild tomatoes from the Gallopagos islands and Chile since some wild plants have the anthocyanin content already. I grow this variety in my garden and have noticed they last on the vine far longer than any other variety. Didn’t know it was due to anthocyanins. Check out this article on OSU’s website:
    http://extension.oregonstate.edu/gardening/purple-tomato-debuts-indigo-rose

    • Thank you. Cool – since Indigo Rose only has purple skin (and not purple flesh like the GM purple tomatoes) it won’t have as high levels of anthrocyanins, but it is possible that anthrocyanins could be contributing to their longer shelf life too. Can’t find any research on it though – would be interesting to see them compared to the GM purple tomatoes

      • True, it is only the skin that develops the anthocyanins –and only where sunlight touches the skin, the rest is normal red. Not that I was trying to debate the need for a GM anthocyanin tomato, just thought you might be interested to know there are other varieties and someones noticed the difference in shelf life even with the seemingly lower content. I would also be interested in a more scientific analysis of the two, and will let you know if I find anything.

      • 🙂 thanks. It looks like Indigo Rose is now available in the UK so I will keep an eye out for them next year – although I guess the purple makes it a bit trickier to tell when they are ripe!

      • There is a guy on the Tomatoville forum who has bred a blue tomato descended from the P20 or Indigo Rose line who has managed to get some anthocyanins inside the tomato. So active blue tomato breeding is happening at a rapid pace these days.

  2. Pingback: The surprise potatoes | Plant Scientist

  3. Also, Joseph Lofthouse is breeding tomatoes with wild tomatoes to produce Highly Outcrossing tomatoes, Frost Hardy Tomatoes, and Tomatoes with gigantic flowers that attract bees and pollinators (As modern tomatoes do not and are highly inbred). You can find him at Garden.Lofthouse.com or he often shares his projects and seeds with us at the Alan Bishop Homegrown Goodness Plant Breeding Forum! Feel free to join us. Many of us are breeding Red-podded peas!

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