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Not Genetically Engineered: Grapes

New York Grapes. Concords I believe, though it's been several years so I may be remembering wrong.

New York Grapes. Concords I believe, though it's been several years so I may be remembering wrong.

Scientific Name: Vitis vinifera

Supposed Genetically Engineered Trait: Large size/seedlessness

The Real Story:

Seedless grapes are descended from several different mutations that all result in the developing embryos of grape seeds to abort prematurely*. You can still find the tiny dead remnants of seeds in seedless grapes. Of course being seedless raises a new question: How do plant breeders work with seedless grapes? (And breeders definitely do work with seedless grapes. For example they’ve developed more cold tolerant seedless grapes that are well adapted to the vineyards springing up along the finger lakes in New York.)

The answer (I had to look this up myself) is that grape breeders can dissect out the seeds of immature grapes (before they abort) and use tissue culture techniques to grow them in a lab. The technique is called embryo rescue and it’s used effectively in lots of situations where plant breeders otherwise can’t get viable offspring. Once a breeder develops a tasty and hardy new breed of seedless grape, multiplying it for distribution is easy, since almost all grape vines grown today are already produced using grafting.

Normally grape seeds produce a plant hormone called gibberellin that, among many other cool roles in plant development, promotes fruit growth. Since seedless grapes, by definition, don’t have seeds, farmers often spray them with gibberellin to increase their size (otherwise seedless grapes are smaller than their seeded relatives). The enlarged seedless grapes created by gibberellin spraying are probably the cause behind uninformed comments like:

Why do “regular sized” grapes look so teeny to me? Oh that’s right, b/c the ones we have at home now are the genetically engineered ones.

Other facts about grapes:

Grapes growing outside of Prairie Moon Winery (near Ames, Iowa). Photo: rwmsn, flickr (click to view photostream)

Grapes growing outside of Prairie Moon Winery (near Ames, Iowa). Photo: rwmsn, flickr (click to view photostream)

I’ve actually fairly familiar with the grape genome, it’s one of the better assembled plant genomes and is great for doing comparisons to other eudicot species since it hasn’t gone through any further duplications since the ancient hexaploidy of eudicot plants. For example one genomic region in grape matches up to four separate regions in Arabidopsis, a species that has gone through two more recent rounds of whole genome duplication.

But enough about genomics. Grapes were originally domesticated in the Mediterranean. People have been making wine from them for thousands of years. The Odyssey talks about Odysseus and his men making wine from grapes at several points.** Wine making is still the primary use of grapes grown everywhere from famous wine regions (like California and France) to good but obscure ones (like the finger lakes of New York) to the truly unexpected wineries (like Iowa).

[This part grabbed from my previous post on grafting] Grapes are a great example of using root stocks to provide disease resistance and climate tolerance while maintaining old flavors, (and no grapes are not a tree but a woody vine). Many of the grapes grown around the world today are old breeds of European grapes that produce the various favors of wine western our culture is accustomed to, grafted on to rootstock from a separate species native to North America which provides resistance against phylloxera, an insect that devastated vineyards around the world. (Yes, disease resistance in the rootstock can sometimes provide protection for the entire plant, and no, I have no idea how it works, but I’m sure others do.)

*As with any complicated system there are a lot more ways to break grape embryo development than for it to work successfully.

**Way back in high school I used that fact to twist an otherwise mind numbingly boring english assignment into a paper on early agriculture and the biology fermentation. As I recall my english teacher was not pleased with me, but it was worth it. 😉

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