How to grow a cacao tree in a hurry

To study the genetics of cacao, the main ingredient in chocolate, scientists clone flowers

Chocolate is made from the pods (shown here) that grow from the trunk of the tropical cacao tree. To reproduce this tree rapidly, scientists clone it.

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Growing a cacao tree — the plant whose pods are made into chocolate — takes patience. It takes three to five years for a cacao seed to become a fruiting tree. Each tree makes a limited number of seeds. And those seeds are not identical to the parent plant. The genes inside the seeds are a mix. Some come from the plant that grows the fruit. Others come from the tree that provided the pollen. That’s a challenge for researchers who study the genetics of cacao plants. As they try to improve features of these trees from one generation to the next, they don’t want to wait years to learn whether a tree contains good genes for specific traits.

And now they don’t have to. Mark Guiltinan and Siela Maximova are plant biologists at Pennsylvania State University in University Park. Their secret: cloning.

They start with a tree that has the genes they’re interested in. These genes might help the tree resist diseases, for example. Or the genes might help the tree grow faster, or make better-tasting chocolate. (The researchers do not insert genes into the tree — it is not genetically modified. Rather, they look for genes that developed in them naturally.)

The scientists snip off tiny pieces of a tree’s flowers. They put the pieces in a germ-free solution. Then they add hormones that make each flower piece start growing into a young plant, as if it were a seed.

In this way, the researchers can create thousands of plants from the pieces of a single flower. These new plants are clones. That means they have the exact same genes as their parent tree — and each other. 

Identical genes are a blessing and a curse. Those genes may make a cacao tree grow lots of pods or keep it from getting a certain disease. But there are many different cacao diseases. Resistance to one disease may not protect the plant against another of them. Because all of these young plants share the same genes, they are all vulnerable to the same pests and diseases. If someone planted an entire farm or plantation with identical cacao trees, a single infection might later on wipe them all out.

Guiltinan and Maximova are very much aware of the problem. “We would never recommend a single variety,” Guiltinan says. Instead, he suggests that cacao farmers plant many genetically different types of trees. Each variety would produce many pods and be resistant to at least one disease. This should help ensure a healthy field — and a crop of delicious cacao.

Alison Pearce Stevens is a former biologist and forever science geek who writes about science and nature for kids. She lives with her husband, their two kids and a small menagerie of cuddly (and not-so cuddly) critters.

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