Beans face stiff competition at drought Olympics

23 September, 2013 by (comments)

Every 4 years, experts from around the world gather for a meeting of the InterDrought Consortium. Think of it as a sort of drought Olympics. The metaphor seems especially apt when you consider that Olympia, the site of the original games in ancient Greece, is a pretty dry place.

Instead of competing with one another and giving out medals, though, InterDrought participants talk about challenges and progress in alleviating an age-old scourge of food production, which is getting much worse now as a result of climate change. In this year’s conference – held in September at Perth, Australia (another dry place) – Steve Beebe, who captains the CIAT’s bean research team, carried the flag for this world-class, nutritionally rich grain legume.

The team and its African partners have scored a number of major victories in recent years, with support from the Bill & Melinda Gates Foundation.

drought-tolerant-beans

After lengthy scientific preparation at CIAT headquarters in Colombia, scientists sent their best drought-tolerant lines for testing near Machakos in eastern Kenya at the Katumani Research Station of the Kenya Agricultural Research Institute (KARI). As a result of this and subsequent evaluations elsewhere, two drought-tolerant bean varieties were released in Rwanda and three in Malawi, while others have been proposed for release in Ethiopia and Kenya. The evaluations in Kenya also put on the winners’ podium several locally selected lines that farmers prefer for their drought tolerance.

At the meeting in Perth, though, Beebe reported that a definitive triumph over drought in tropical bean crops will be even more difficult to achieve than previously expected.

“According to recent on-farm experience in Ethiopia and Nicaragua,” he said, “low soil fertility inhibits the expression of drought tolerance. While our improved materials still have an edge over drought-susceptible lines under low soil fertility, the advantage is not as big.”

An estimated 80% of bean production in Central Africa is subject to soil phosphorus deficiency, while for Eastern Africa, the figure is 65%. African colleagues attending the InterDrought meeting showed a keen interest in Beebe’s results, because they’re familiar with the tough stress scenarios that bean crops face in the region.

Part of what makes the common bean less resilient than other staple foods is its privileged evolutionary background. The wild ancestor of bean originated in a mid-altitude forest environment of tropical America that is characterized by moderate temperatures and organic soils rich in nutrients. To compete with the surrounding vegetation, the plant developed an aggressive climbing habit. But its strong vegetative growth came at the expense of flowering and reproduction.

That’s why beans are hard pressed to give winning grain yields in farmers’ fields, particularly under the tough growing conditions that prevail in Africa. Domestication partially overcame this limitation, but it has still taken years of breeding for drought tolerance to change the bean plant’s ancestral habit of delaying seed production when faced with water shortage.

By tapping the rich genetic diversity of beans, CIAT scientists have succeeded in identifying and using certain traits in bean roots and shoots that contribute to drought tolerance. This accounts for the bean breeding successes presented at the InterDrought Conference. At the same time, our scientists have developed bean lines that perform well under low soil phosphorus and others that show tolerance to aluminum toxicity.

Not a bad score card for a crop that was never meant to be grown in a warm, dry climate and poor soils. Yet, modeling studies suggest that in regions where soils are infertile (and farmers can’t afford to apply much fertilizer), the increased drought caused by climate change will have disastrous effects on bean yields.

“We don’t yet know much about the interactions between soil constraints and drought, especially on farm,” Beebe said. “To keep improving farmers´ bean yields in a changing climate will require better agronomy, but we’ll also have to find the right balance in our breeding program between multiple stresses.”

In other words, scientists must now win what amounts to an agronomic and plant genetic triathlon – finding ways to get the upper hand on drought and at the same time low soil phosphorus and aluminum toxicity.

The search is on for Nike beans!

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