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Tales from a Plant Addict

Fun (& a few serious) facts, tips and tricks for every gardener, new and old.

Blue Tomatoes


For the ninth year in a row, Macon County Master Gardeners, Green Thumb community gardeners and I have planted a selection of tomato cultivars for our annual Tomato Taste Panel. This year we will taste tomatoes on Wednesday, September 3rd at 1 and 6 p.m. During this event, we invite the community to join us in tasting over 20 different heirloom and hybrid tomato cultivars. The goal is to introduce people to the incredible diversity among tomato cultivars, and encourage people to try new ones in their garden.

Each January we select the cultivars for that year's Taste Panel. Honestly, there is nothing scientific about how we do it. Typically we try to have diversity in size, color and type of tomato (slicer, paste, etc). If there are new hybrids available that sound promising, we grow some. If there are heirlooms that we haven't tried before, we grow those. We also include some "old reliable" cultivars in the Panel that we know are crowd favorites so there is something for folks to compare to at Taste Panel time.

My education is in genetics and plant breeding, so I have a tendency to be drawn to strange and unusual plants. So it comes as no surprise that I love to find really unusual tomatoes to grow. We have grown white tomatoes, striped tomatoes, hollow tomatoes, even fuzzy tomatoes. So it comes as no surprise that I was drawn to the selection of deep purple or "blue" tomatoes offered in a couple of the seed catalogs that graced my mailbox last winter.

We are growing the following deep purple "blue" cultivars for the 2014 Taste Panel: 'Indigo Rose', 'Blue Berries' and 'Blue Beauty'. I have 'Indigo Rose' growing in a container on my patio, and 'Blue Beauty' in a raised bed. 'Blue Beauty' looks like any other tomato plant in my garden, except for the deep purple color developing on the stem end and shoulders of the tomatoes. 'Indigo Rose' is a very different looking plant overall, and the fruits have stopped many a seasoned gardener in their tracks this summer.

The fruits of 'Indigo Rose' are large cherry-type tomatoes, but as they grow, any part exposed to the sun develops a deep purple, almost black color due plant pigments called anthocyanins. My husband mistakenly assumed that the dark color was an indication of ripeness, but it has nothing to do with being ripe. The dark color is only in the skin and outer layer of the fruit's flesh-- most of the fruit ripens to a familiar red color.

So the question remains—how in the world do you tell if it is ripe? The entire tomato will soften somewhat and be a dull purple when ripe, and any shaded portions that remained green will ripen to a familiar red.

I was finally able to eat some ripe 'Indigo Rose' tomatoes recently. I guess I was expecting something unusual given its color, but it just tasted like a homegrown tomato. The darkening of the tomatoes to a deep purple-blue color has been pretty dramatic. The plants themselves look different-- the stems and leaves have some purple coloring, and they are very stiff and upright in form. The Master Gardeners and I were comparing notes recently on how this cultivar looked at different locations; it is so different looking we were concerned something might be wrong!

'Indigo Rose' is credited with being the first improved tomato cultivar with anthocyanins in its fruit. Oregon State University Professor Jim Myers developed the variety as part of his conventional vegetable breeding program with the goal of breeding higher levels of antioxidants such as anthocyanins into tomatoes.

Many people have taken one look at the unusual looks of 'Indigo Rose' growing on my patio and jumped to the conclusion it is a genetically modified organism (GMO). It is NOT a GMO, where genes are artificially inserted via laboratory techniques. The genes that produce the anthocyanins naturally occur in some wild species of tomato. The original crosses were done back in the 1960's, crossing standard tomato cultivars with wild tomato species from Chile and the Galapagos Islands. Professor Myers' graduate students worked with these original crosses to create a population from which 'Indigo Rose' was selected.

But why breed for a high anthocyanin tomato? Although 'Indigo Rose' and other blue tomatoes are getting a lot of attention as a novelty in the garden, the hope is they might have some health benefits for those that eat them. Anthocyanins are classified as antioxidants, chemicals that are hypothesized to be able to neutralize other harmful chemicals in the body, preventing damage to the body's tissues.

Antioxidants first received attention when researchers described the "French Paradox" where certain populations of red-wine drinkers in France and Italy had much lower incidents of heart disease than other populations in Europe and North America. It is widely debated whether the observed health difference is due to antioxidants present in red wine.

Anthocyanins are class of plant pigments that includes several different specific chemicals; all are part of an even larger group referred to as flavonoids. As the name suggests, flavonoids include compounds often associated with flavor. In the case of 'Indigo Rose' though, the anthocyanins do not impart any specific flavor to the fruit. High anthocyanin tomatoes like 'Indigo Rose' reportedly have intense flavor, but this is hypothesized to be due to other genes being upregulated along with anthocyanin production.

Concentrations of anthocyanins in 'Indigo Rose' and other blue tomatoes vary widely depending on growing conditions. Compared to other crops like blueberries, 'Indigo Rose' contains less anthocyanins. However, people consume a lot more tomatoes per year than blueberries. On average, Americans consume 90 pounds of tomatoes per person per year compared to only 1 pound of blueberries per person per year.

If the anthocyanins in blue tomatoes prove to be a real health benefit, tomatoes could be a good way to deliver that benefit to consumers. Even if the hypothesized health benefits are never proven, most Americans can't go wrong in consuming more fresh produce.

Interested in seeing and tasting 'Indigo Rose' and over 20 different tomato cultivars? Join us on Wednesday, September 3rd at 1 and 6 p.m. for the 9th Annual Tomato Taste Panel. Please call the Macon County Extension office at 877-6042 or web.extension.illinois.edu/dmp to register.



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