Potatoes
Photo: Scott Bauer/USDA ARS

Scientists are trying to revolutionize potatoes and, in the process, cure the tubers’ depression, the result of generations of inbreeding.

Potato depression is obviously nothing like human depression, of course. Potatoes reproduce through cloning, so their genome is laden with mutations. Those mutations could result in things like stunted growth or shorter lifespans. A team of Chinese scientists looked for a better way to make potatoes reproduce, and along the way learned more about the genetics behind spuds’ “inbreeding depression.”

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You probably have seen sprouts, or eyes, grow out of potatoes. That’s how farmers plant new potatoes—by cutting up old ones and letting those eyes germinate into new plants. Generations of cloning means that harmful genetic mutations remain in the genome, but the plants have a buffer against that—most varieties are “tetraploid,” meaning they have four sets of chromosomes. If there’s a bad mutation on a gene, there are presumably three other working versions of the gene.

Farmers haven’t minded growing the potatoes through cloning, rather than from potato seeds with two potato parents, because the potato industry has long thought that the crops grown from clones produced more potato than those grown from potato seeds with two parents.

But there are drawbacks to these tetraploid potatoes. They could hide lots of different gene combinations in their complex genomes, so the result of mixing that genetic information up in sexual reproduction leads to offspring that are worse-off than their parents, according to one 2016 paper. That can make selective breeding to create new potato lines difficult.

A team of scientists meeting in 2016 at the University of Wisconsin-Madison proposed a new idea—reinventing the potato as a diploid crop, one with two, rather than four, sets of chromosomes. The researchers would then be able to selectively breed (and then inbreed) the resulting potatoes as is commonly done with other crops, and create fixed lines of potatoes based on color, shape, texture, and other properties that are easier to control.

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Teams of researchers are now working to realize these diploid potatoes. But one issue is that these diploid potatoes would expose generations of inbreeding. So the team behind the newest paper, composed of researchers from China and Singapore, identified 344,831 potential mutations upon sequencing their potatoes. Half were rare, and 27 percent were already present in the potato’s ancestral plant, a wild potato species called Solanum candolleanum. These harmful mutations varied from minor things like stunted growth and lower reproductive fitness to major things like the plant’s death.

The new work serves two key purposes, according to the paper published in Nature Genetics. The researchers hope it will serve as a basis for designing these new diploid potato lines, and hopefully to understanding how years of clonal propagation can affect the overall fitness of a plant species more generally.

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Will we ever see one of these new diploid potatoes? The international team of scientists behind the effort think it could be revolutionary for potato breeding, opening up the potato to the benefits of selective breeding, hybrid breeding, and gene editing. But it will take work: Not only would it require drastic changes to the way farmers produce one of the world’s most common staple crops, but one of the world’s major potato buyers, McDonalds, has twice refused to buy genetically modified spuds.

Just know that scientists are actively working to reinvent the potato. Also, inbreeding is bad and can lead to depression, if you’re a potato.

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