Black beans, kidney beans, pinto beans, navy beans and pink beans—varieties of what is called the common bean—provide essential protein and vitamins the world over, especially in Latin America and Africa. But according to a recent climate model, increasing temperatures could take those beans off the table for up to 50 percent of their growing areas by 2050, making temperature rise a greater threat to this staple food than even drought or disease.



In response, the International Center for Tropical Agriculture (CIAT) dug into its seed repository and struck gold. After testing more than 1,000 bean varieties they had developed during other projects, investigators identified around 30 that revealed some ability to produce seeds in spite of toasty night temperatures. Those beans have the potential not only to survive increasing temperatures, but to thrive. In fact, they might even expand the area where beans can be grown.



The researchers focused on night temperatures because common beans, which are a primary source of protein for over 400 million people, can produce viable pollen only if the nights are cool. They often do best at raised elevations, where nighttime temperatures reach no higher than 18 degrees Celsius (around 64 degrees Fahrenheit).



“The common bean originated in the hills and mountains, so it’s not especially well adapted to coastal areas and high temperatures,” says Stephen Beebe, CIAT’s bean program leader. “Now, with climate change, the high temperatures aren’t staying down at the coast—they’re going up the hill.”



Researchers had calculated that beans able to withstand a temperature rise of about 4 degrees Celsius (7.2 degrees Fahrenheit) would be able to stay in most of today’s bean-growing locations until at least 2050 and potentially expand into other areas where beans currently cannot grow due to the heat. Beebe and his colleagues therefore decided to test 1,000 candidates in Colombia’s Caribbean Coast, a low-altitude area where night temperatures can hit that level, heating up to 23 or 24 degrees Celsius. Many of the selected plants had previously been bred to withstand drought, resist disease and have higher iron content. The ones that thrived when grown in the open air during the experiment were easy to find: although most of the plants tested produced no seed pods at all or generated shriveled seeds, 30 lines managed to produce viable seeds—up to 1,000 kilograms in one trial, Beebe says, when the others yielded nothing. Beebe announced the discovery Tuesday at a conference in Addis Ababa, Ethiopia. CIAT's research was done with the support of CGIAR, an international partnership of organizations working on food security research.*



Many of the beans that beat the heat had a common ancestor in their family trees: tepary beans, which are tiny, drought- and heat-tolerant beans that grow in the southwestern U.S. and northern Mexico. They have fallen out of favor because of their small size, but at one time the near-desert’s inhabitants would rush out and plant them after a rain shower—often the only time the plants would have access to water for their whole lifespans. So it makes sense that beans with tepary ancestry might have a leg up on heat tolerance as well as drought tolerance.



“Very little survives nighttime temperatures of 23 degrees or higher,” says Timothy Porch, a plant research geneticist with the U.S. Department of Agriculture who has worked on developing heat-tolerant beans in Puerto Rico. “Having varieties that produce at 23- or 24-degree field-condition nighttime temperatures is significant.”



Paul Gepts, the leader of the University of California, Davis’s bean breeding program, says the finding is very encouraging. “People have been interested in heat tolerance for a long time, and what you see here is the cumulative progress of many years of work involving genetics, plant breeding, plant physiology, even plant morphology and geographic information systems,” he says.



Moving forward



Unlike some other crops, such as corn and soybeans, there is little research on genetic engineering in beans. Beans have high variability to start with, so large seed banks and databases of genes—such as one that Gepts’ lab is developing and one that Porch’s group is creating in collaboration with Beebe’s—allow researchers find and develop traits through conventional breeding.



Similarly, most other researchers who have worked on heat tolerance in crops have focused on breeding (and the same is true for drought tolerance). Cotton, chickpeas, rice and wheat, as well as corn, have all been tested for their reactions to heat, and some groups have bred more heat-tolerant varieties or are in the process of breeding them. There are a few genetic engineering projects, however. One research team has identified a gene in rice and grapes that helps them withstand heat and is working to incorporate it into wheat, and another group extracted an E. coli gene that allows tobacco plants to cope with heat stress.



Gepts says agricultural researchers have to decide, in the face of climate change, whether to improve on existing crops that farmers are comfortable with in a given region or ask them to switch to planting an entirely new food that would survive increased heat and irregular rainfall. Beebe’s work, Gepts notes, “says we can keep working on these crops and still provide sufficient yield to feed the people.”



The next step is to breed the heat-tolerant beans to fit different areas—different sizes, colors and textures are preferred in different places, and any location’s farmers will have different requirements—and to incorporate additional beneficial traits, like disease resistance or extra nutritional value, that researchers have been able to incorporate into other beans.



Although the task sounds complex, Beebe has high hopes. It is encouraging, he says, that many of the bean plants his group tested had acquired heat tolerance without help from researchers. This is a good sign that the same characteristic can be passed on to new plants; the set of traits might be complex genetically, but they have been passed along successfully already in plants that were being selected for other characteristics.



“As breeders we need to be thinking ten, twenty years ahead at least, to what’s coming,” Porch says. Future varieties of bean will have to contend with even higher temperatures, new levels of drought, changing insect pressure and different diseases. “The breeding work never ends, because the environment is continuously changing,” he says. Yet with large seed banks, broad collaboration and mounting understanding of individual crops’ genetics, researchers are getting a head start.



*Editor's Note (3/26/2015): This sentence was added after posting.