Advances in Apples

If “an apple a day keeps the doctor away,” it’s rather surprising there’s still a need for doctors, considering Canadians consume around 11 kg of apples per person per year.

They can choose from a bewildering array of apple cultivars, too (more than 7,500 are known), from the crisp and tart (Macintosh) to the soft and sweet (Red Delicious).

But the quest for a better apple, it seems, is never-ending.

The domestic apple, Malus domestica, is a member of the family Rosaceae—the same family as roses, which may explain why apple blossoms are so appealing. Malus domestica’s wild ancestor, Malus sieversii, still grows wild in the mountains of Central Asia.

The legend of Johnny Appleseed to the contrary, commercially apples are propagated by grafting, a form of cloning practiced for a couple of millennia now. Breeders graft the shoots and branches of a tree whose fruit they like (the scion) onto a new trunk and root system (the root stock), creating a hybrid. If not for this, there would be no consistent apple varietals: if you plant a Golden Delicious seed, you won’t get Golden Delicious apples from the resulting tree, because, the seed contains too much genetic variability. In fact, you’ll likely get something more like a crab apple.

The choice of rootstock matters: different rootstocks bring out different qualities in the scion. Nobody really understands the process very well, though. Researchers in Pennsylvania are trying to learn more. Tim McNellis, assistant professor of plant pathology at Penn State University, says it’s not a case of genes migrating from the rootstock to the scion; rather, the rootstock somehow turns on genes that are already present.

McNellis is concentrating on the Gala apple (an important cultivar in Pennsylvania), and one trait: disease resistance. He grafted Gala scions onto two different rootstocks, then scanned the genetic makeup of each to see which genes were active. He found that one kind of rootstock turned on twice as many stress tolerance genes in the scion as the other—and that that scion was more resistant to a bacterial disease called fire blight. This year a team of researchers will be examining 20 different rootstock varieties. If the research bears fruit (sorry) then growers will have new information about the best rootstock to use—and plant breeders will understand more about how rootstocks affect scions.

Meanwhile, in New Zealand, researchers at the fruit science company HortResearch have come up with an apple that’s red—not just on the outside, but all the way through. And they’re working on green, gold and purple ones.

The company began work on a naturally occurring red-fleshed apple in 1998. Its external appearance, eating qualities and storage capability didn’t meet commercial needs, but by crossing it with high-quality white-fleshed apples, HortResearch created apples with flesh ranging in colour from white to pink to purple. They’re focusing on the red-fleshed apple because the colour is so appealing.

HortResearch is home to the world’s largest database of fruit genes and compounds and is in the process of making public 50,000 apple DNA sequences, called Expressed Sequence Tags (ESTs), that identify active genes—genes that actually do something. Using their EST database, the HortResearch scientists practice smart breeding, using genetic screening to pick out the best breeding prospects from among tens of thousands of seedlings. Being able to hone in on the best candidates for producing desirable fruit should greatly reduce the time necessary to create a viable new cultivar, from a couple of decades to as little as five or six years.

HortResearch emphasizes it is not genetically engineering its apples: it’s using standard breeding techniques. Researcher Abhaya Dandekar at the University of California, Davis, however, has been genetically engineering apples, and he’s come up with fruit with more sorbitol and less sucrose and fructose, three sweet compounds all naturally found in apples. Since sorbitol has only 2.6 calories per gram, 45 percent less than sucrose and fructose, what he’s really developed is a low-calorie apple. And although he used direct genetic modification, he says plant breeders could achieve the same results with regular breeding techniques. Not only that, he believes related fruits such as pears, peaches, plums and cherries could also be produced in low-calorie varieties.

Pomologists (apple scientists), it seems, are not resting on their, um, blossoms. Though apples may keep doctors away from people, apparently they actually attract people with doctorates.

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Though engaged in a kind of science some might find seedy and ripe for graft, pomologists cling to their roots, attempting to stem the doubts that worm their way into the public's heart, polishing pomology's reputation, in the hope that someday its core value may be better recognized, and its appeal may yet blossom and grow.