Unraveling the Historical Journey of the Green Bean: A Story of Evolution, Migration, and Climate Adaptation

The mung bean, commonly known as green gram, has played a vital role as a cheap source of protein in regions where access to meat is limited. Over 4,500 years, the cultivation of this humble legume has sustained civilizations throughout its history. While its migration routes and cultivation expansion have been a mystery, a new study led by researchers at the USC Dornsife College of Letters, Arts and Sciences, published in eLife, reveals insights into this hardy crop’s winding odyssey.

many rows of graded seeds of various sizes, shapes and colors in labeled boxes.
Vavlov Institute of Vegetable Industry in Russia. (Photo: Eric J. Von Wettberg.)

The study, co-led by Sergey Nuzhdin, a professor of biological sciences at USC Dornsife, used cutting-edge genomic techniques to trace the evolutionary trajectory of the mung bean. The team analyzed mung bean seeds from three global seed banks, including the Australian Diversity Panel, the World Vegetable Center in Taiwan and the Vavilov Institute of Plant Industry in Russia.

The research unveiled a distinctive cultivation path and shed light on the factors that influenced its expansion. Contrary to previous hypotheses based on the geographical proximity between South and Central Asia, genetic evidence suggests that the mung bean first spread from South Asia to Southeast Asia, and then finally reached Central Asia, including Western China, Mongolia, Afghanistan, Iran and Russia.

Climate adaptation

Nuzhdin and his team of international scientists used an interdisciplinary approach that examined population information, environmental conditions, laboratory and field empirical investigations, and historical records from ancient Chinese sources. Through this analysis, they found that divergent climatic conditions and agricultural practices across Asia shaped the unique trajectory of mung beans, not deliberate cultivation choices by humans.

Nuzhdin was surprised that evolution was not solely driven by human activity through domestication, but instead was intricately intertwined with the mung bean’s adaptation to the different climates it encountered during its journey.

What the research uncovered was the existence of two distinct mung bean adaptations, each favored in specific geographic locations. The southern variant, native to South Asia before 1068-107 AD, is characterized by larger seeds, favoring higher yields in regions with torrid climates. In contrast, the northern variant, originating in northern China around AD 544, exhibited drought tolerance and a short growing season during the summer planting season. The mung bean later spread to the rest of China and Southeast Asia, including Cambodia, Indonesia, the Philippines, Thailand, Vietnam and Taiwan.

Neatly planted rows of crops.
Taiwan’s World Vegetable Center tests different genetic materials to grow and breed mung beans. New USC Dornsife research will illuminate which genetic materials to use for optimal breeding and cultivation. (Photo courtesy: World Vegetable Center, Taiwan.)

Genetic variations

While the study’s historical revelations are compelling in their own right, their implications have relevance to new ways of growing crops. The mung bean genetic makeup, including short growing season and resistance to extreme heat, has significant potential to mitigate the impact of climate change on agriculture. Particularly in Southeast Asia, where prolonged heatwaves and the severity and impact of flooding threaten valuable agricultural areas, these genetic variants could prove to be a game changer in the face of climate change.

“Our findings offer a critical roadmap for farmers aiming to improve mung bean production in the face of climate change forecasts, especially in southern regions. This fundamental research is of immense importance in guiding the selection of genetic materials for breeding programs,” Nuzhdin said.

About the study:

The study, Environment as a Limiting Factor of the Historical Global Spread of Mung Bean, was published in eLife. The components of USC were funded by the United States Agency for International Development and the Zumberge Foundation. Funding was also provided by the Ministry of Science and Technology, Taiwan; the Australian Center for International Agricultural Research; the long-term strategic donors of the World Vegetable Center; The Republic of China (Taiwan); the UK government; Germany; Thailand; Philippines; Korea; and Japan. The Russian Scientific Fund Project and the Ministry of Science and Higher Education of the Russian Federation also contributed.

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