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.
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clone An exact copy (or what seems to be an exact copy) of some physical object. (in biology) An organism that has exactly the same genes as another, like identical twins. Often a clone, particularly among plants, has been created using the cell of an existing organism. Clone also is the term for making offspring that are genetically identical to some “parent” organism.
gene (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
generation A group of individuals born about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet are referred to as belonging to a particular generation of humans. The term also is sometimes extended to year classes of other animals or to types of inanimate objects (such as electronics or automobiles).
genetic Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.
germ Any one-celled microorganism, such as a bacterium, fungal species or virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.
hormone (in botany) A chemical that serves as a signaling compound that tells cells of a plant when and how to develop, or when to grow old and die.
infection A disease that can spread from one organism to another. It’s usually caused by some sort of germ.
plantation A site where some species of tree or other valuable, wild-like plant (such as coffee, banana or tobacco) has been planted as a crop.
resistance (as in disease resistance) The ability of an organism to fight off disease.
trait A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.
variety (in agriculture) The term that plant scientists give to a distinct breed (subspecies) of plant with desirable traits. If the plants were bred intentionally, they are referred to as cultivated varieties, or cultivars.