Decoding Blood Oranges: Discovery of the Ruby Gene

Blood orange and Valencia orange compared
The Moro blood orange and a Valencia orange

The amazing raspberry-ruby grapefruit flavor of blood oranges is a special treat, but you have to take advantage of their short seasonal availability. That may change soon. Researchers have identified the gene responsible for the color and health benefits, and they are trying to develop a new, more widely accessible variety.

The Uniqueness of Blood Oranges

We have been feasting on beautiful blood oranges from our local farmer’s market for weeks now, but our vendor has just ended his season. What to do? We love them so much that I bought a tree to add to our suburban mini-orchard.

The lovely red-blushed skin of the blood orange is unique among sweet oranges, from which it was derived centuries ago. Historians believe it is a mutated form of the common sweet orange, and its early cultivation can be traced to Southeast Asia, China, the Middle East and Italy.

Blood orange juice compared to Valencia orange juice
Blood orange juice compared to Valencia orange juice

Anthocyanins Abound with Health Benefits

The first time you cut one open it’s shocking to see the dark blood colored pulp inside. Ditto for the freshly squeezed juice. The color is caused by anthocyanins, which are flavonoids credited with various health benefits: reducing oxidative stress damage in cells, reducing cardiovascular risk factors, and even resistance to obesity. These effects are well known for foods high in anthocyanins, and blood oranges produce a particularly high amount if grown under the right conditions.

Of the several different types of blood oranges, which include Tarocco, Moro, and Sanguigno, the Moro is the most dramatically  pigmented.

Special Cultivation Requirements

The blood orange is grown in sunny climates as are other citrus varieties, but it has an unusual requirement for the right amount of exposure to cold temperatures. The deep crimson color is dependent on exposure to cold, as was confirmed by a team of researchers funded by the EU at the John Innes Centre in Norwich, that recently identified the gene responsible for the red color.

They discovered that the gene they named Ruby, is actually activated by cold. So this limits the areas where blood oranges can be cultivated, because without the right amount of cold, it won’t develop the red color, thus it won’t have the same health benefits. The researchers would like to introduce the Ruby gene into sweet oranges and disengage it from dependency on cold temperatures.  This way it can be cultivated widely to bring the health benefits of anthocyanins to more people.

So I’m feeling especially lucky that the San Francisco area where we live has the right growing conditions for my new Moro blood orange. It will be interesting to see if the variety developed by the scientists at Norwich will have the same flavor and floral aroma.

A high bar to reach, indeed.

The research paper will be published in the journal Plant Cell.

Butelli, E., Licciardello, C., Zhang,Y.,  Liu, J., Mackay, S., Bailey, P., Reforgiato-Recupero, G., and Martin, C. (2012). Retrotransposons control fruit-specific, cold-dependent accumulation of anthocyanins in blood oranges. Plant Cell. 10.1105/tpc.111.095232 in press.

 Photos: Urban Artichoke

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