Wild relatives of beans retain useful drought resistance

The plants we turned into crops were honed by evolution to tackle the stresses they found in their environment. Since domestication, some crops will have lost adaptations. A study by Jorge C Berny-Mier y Teran and colleagues set out to find if the wild relatives of the common bean, (Phaseolus vulgaris) still had adaptations to drought stress. If they did, the team also wanted to know if the origin of a population of plants reflected their drought adaptation. 

“More than half of the area of common bean production is grown under drought conditions and, after diseases, drought stress is the second most important factor that reduces productivity,” Berny-Mier y Teran and colleagues wrote in their paper. “In bean, drought stress not only causes significant reduction in biomass, seed weight and yield, but also changes the nutritional quality of the seeds. Breeding for higher yields under drought would increase the area suitable for bean production by 31 % above the current distribution.”

To find out how well adapted the wild beans were, the scientists gathered over a hundred seeds and tested them under drought conditions. Planting the seeds in clear plastic tubes enabled them to track the growth of roots as well as shoots.

“One of the key findings was the effect that drought promoted deeper root growth,” wrote Berny-Mier y Teran and colleagues in their paper. “At the same time, canopy growth was suppressed but comparatively less change in root biomass was observed. Based on other lines of evidence, this would reflect soil water deficit avoidance. When comparing wild types with their domesticated counterparts, domesticated forms were more productive in terms of biomass and rooting depth. Selection during domestication and crop development increased both root and shoot mass, root depth and the proportion of biomass invested in roots, as found in Pisum sativum and wheat. However, in this research wild accessions were more efficient at reaching deeper soil strata relative to the amount of biomass invested in roots, suggesting that competition for soil water may be higher in wild than in domesticated forms.”

The team concluded that while the domesticated bean had advantages, there were still elements of the wild bean that could benefit farmers. “Domesticated beans were more vigorous in general: they produced more biomass, above and below ground, and developed deeper roots. However, wild beans showed reduced phenological delay as well as smaller reductions in root and shoot biomass accumulation under drought stress, traits that could be useful to improve the domesticated gene pool.”