This spud’s for you: A breeding revolution could unleash the potential of potato
By Erik Stokstad, Feb. 7, 2019
Published in Science
THE SACRED VALLEY OF THE INCAS IN PERU—On a bleak, brown hill here, David Ellis examines a test plot of potato plants and shakes his head. “They’re dead, dead, dead,” he says. Pests and lack of rain have laid waste to all 17 varieties that researchers had planted.
It is a worrying sign for Ellis, the now-retired director of the gene bank at the International Potato Center (CIP) in Lima. People have grown potatoes in this rugged stretch of the Andes for thousands of years. In recent years, that task has gotten tougher, in part because of climate change. Drought and frost are striking more often. The rains come later, shortening the growing season. And warmer temperatures have allowed moths and weevils to encroach from lower elevations.
To find potatoes that can cope with those challenges, researchers and Peruvian farmers are testing dozens of the 4350 locally cultivated varieties, or landraces, kept in CIP’s refrigerated storage. The plants in this plot fell short. “Native landraces evolved over time,” Ellis says. But, he says, climate change is happening “too fast for these varieties to adapt.”
In Peru and around the world, enhancing the potato has become a high priority. It is the most important food crop after wheat and rice. Potatoes are already a staple for 1.3 billion people, and the nutritious tubers are becoming increasingly popular in the developing world. Keeping up with the demand means adapting the potato to various soils and climates. It must also resist new threats from pests, disease, heat, and drought.
Unlike other major crops, however, the potato has not had a breeding breakthrough of the kind that helped dramatically boost yields during the Green Revolution of the 1950s and 1960s. The reason is that creating a new potato variety is slow and difficult, even by the patient standards of plant breeders. Commercial varieties carry four copies of each chromosome, which forces breeders to create and test hundreds of thousands of seedlings to find just one with the desired combination of traits. Readying a new variety for farm fields can take a decade or more.
Many countries continue to plant popular potato varieties that have remained essentially unchanged for decades. But new approaches, including genetic engineering, promise to add more options. Potato breeders are particularly excited about a radical new way of creating better varieties. This system, called hybrid diploid breeding, could cut the time required by more than half, make it easier to combine traits in one variety, and allow farmers to plant seeds instead of bulky chunks of tuber. “It will change the world tremendously,” says Paul Struik, an agronomist at Wageningen University in the Netherlands.
To breed a better potato, it helps to have plenty of genetic raw material on hand. But the world’s gene banks aren’t fully stocked with the richest source of valuable genes: the 107 potato species that grow in the wild. Habitat loss threatens many populations of those plants. In a bid to preserve that wild diversity before it vanishes, collectors have made their biggest push ever, part of a $50 million program coordinated by the Crop Trust, a charity based in Bonn, Germany.
The collectors and breeders are racing against warming, drying, and the proliferation of pests. “Because of climate change,” says Nigel Maxted, a conservation biologist at the University of Birmingham in the United Kingdom, “we require higher levels of diversity than ever before.”
The closest ancestors of cultivated potatoes evolved in the Andes, where people domesticated the plant at least 7000 years ago. After the Spanish brought the tuber to Europe in the 16th century, it remained a botanical curiosity and was mostly fed to livestock. Europeans began to eat potatoes in earnest only in the 1800s, during the famines of the Napoleonic Wars.
Once the potato caught on, there was no turning back. The plant can grow in cold climates and poor soil, and in some places yields several crops per season. Once harvested, the energy-rich tubers, packed with vitamin C, can be stored for months and cooked in many ways. A hectare of potatoes can provide up to four times the calories of a grain crop.
Like rice and wheat, the potato was a target for improvement during the Green Revolution. Yields increased thanks to fertilizer and improved farming techniques, but they didn’t skyrocket. Potato breeders achieved no genetic gains such as the one that produced wheat with short, sturdy stalks that can bear more grain.
Still, global potato production has steadily grown. China has doubled its harvests over the past 20 years. It now grows more than twice as many potatoes as India, the next-biggest producer. Uzbekistan and Bangladesh, among other nations, have come to depend on the potato for food security. In 2005, developing countries for the first time grew more potatoes than the developed world. Many African countries are aiming to boost production.
To reap bigger harvests, farmers will have to manage many risks, including disease. The potato’s greatest scourge is the funguslike pathogen Phytophthora infestans, which causes a disease called late blight. The pathogen unleashed the Irish potato famine in the mid–19th century, and plant breeders have struggled ever since to rein it in. “Phytophthora is always evolving and overcoming resistance,” says Jadwiga Śliwka of the Plant Breeding and Acclimatization Institute in Młochów, Poland. Rich countries use fungicides to minimize the devastating losses from late blight. But in developing countries, 15% to 30% of the crop is ruined.
Then there is heat and drought, which climate change is exacerbating. In some parts of the world, farmers are planting their crop earlier so that it matures before the nights get too hot, which prevents tubers from forming. But eventually farmers will need hardier plants. “We focus on developing a robust potato that will perform better in a stressful environment,” says Thiago Mendes, a potato breeder with CIP’s regional office in Nairobi. “Our target is food security.”
Read the full article in SCIENCE