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Heat-beating beans resist climate change

Newly tested varieties show promise in surviving higher temperatures

Pollen in the newly identified varieties is viable at higher temperatures, allowing seed pods to form. CIAT

Beans are a staple for hundreds of millions of people, mostly in Latin America and Africa. But these legumes, which originated in cool highlands, are particularly sensitive to excessive warmth—so much so that by 2050, climate change might cut in half the amount of land suitable for growing them. Plant breeders with the International Center for Tropical Agriculture (CIAT) in Cali, Colombia, are aiming to fix that problem. Using samples from gene banks, they recently identified 30 varieties of common beans that can stand up to temperatures that would otherwise cause the crops to fail.

The advance is "pretty novel and interesting," says Scott Jackson, a bean geneticist at the University of Georgia, Athens, who was not involved in the study.

Worried about the impact of rising temperatures, a group at CIAT led by plant breeder Stephen Beebe examined more than 1000 bean varieties stored in gene banks. Other researchers had previously bred these varieties to cope with drought and poor soil. In many cases, they had crossed common beans (Phaseolus vulgaris)—which include black beans, kidney beans, and pinto beans—with a distant relative, the tepary bean (Phaseolus acutifolius). Tepary, which grows in northern Mexico and the southwest United States, is not well suited for farming—it has small beans and is prone to soil infections—but it resists drought and heat.

Here's the trouble with heat. Typically, common bean yields will start to decline once temperatures exceed 18°C to 19°C at night. That's when the bean plants flower and undergo pollination. But excessive heat interferes, somehow hindering the plants' ability to set seed. It also makes the plants grow less efficiently.

So Beebe and his colleagues deliberately planted samples of these 1000 varieties in two places even hotter: the lowlands along the northern coast of Colombia and a research field at the University of Tolima, southwest of Bogotá. During the field season, the temperature at night never dipped below 23°C.

Then the researchers checked for seed pods, a sign that pollination has been successful. Only 30 lines had coped. Most of these lines had tepary as a parent, suggesting its DNA was helping the plants tolerate heat. It's not easy to get heat tolerance from tepary into common beans, says James Kelly, a bean breeder at Michigan State University in East Lansing, who was not involved in the study. "If they have achieved that, which this hints at, they've made quite remarkable progress."

In other measurements, pollen viability in the six best beans exceeded 64%, compared with 20% in heat-susceptible varieties; ­optimal conditions yield about 80% viability. "I'm really happy with the progress," Beebe says. He will present the results, which have not been peer-reviewed, tomorrow at a meeting in Addis Ababa for donors to the CGIAR Fund, which supports research at CIAT and related centers.

"Heat tolerance is a very important trait for bean production in Central America and the Caribbean," says James Beaver, a plant breeder at the University of Puerto Rico, Mayagüez, who was not involved in the study. "The release of heat-tolerant bean cultivars should help farmers to cope with anticipated changes in the climate."

Much testing remains before the varieties can be released to farmers, a process that could take several years. Luckily, the National Institute of Agricultural Technology in Nicaragua has already developed one of these varieties, SEN 52, for drought resistance. They released it as a commercial variety named INTA Negro Precoz in 2013. In Beebe's tests for heat tolerance, it was also one of the best-performing varieties. 


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