New Research Finds Unique Crop Diversity, Struggle to Save It

The high-protein Phaseolus bean is a staple of the local diet, with every household growing the crop for home consumption and only one in five farmers selling it to local markets.

And while most of the native farmers practice modest subsistence farming to feed their families, they also hold the key to conserving bean diversity unique to the Sierra Juarez region that is among the world’s highest. Their in-field experimentation and management techniques are vital in preserving this genetic variation.

A group of researchers from the University of California-Davis set out to learn more about this farmer-led conservation management of Phaseolus beans occurring in the Santa María village, and how farmers are adapting to environmental pressures. “We wanted to see how farmers are reacting to this global climate change,” says Paul Gepts, a professor of Plant Sciences at UC-Davis who co-authored the study just out in the new July-August issue of Crop Science. Gepts is also a more than 30-year member of the Crop Science Society of America and American Society of Agronomy.

Phaseolus vulgaris, the most economically and nutritionally important Phaseolus species, is adapted to warmer temperatures at lower altitudes. Two races, Mesoamerica and Jalisco, have branched from this species. While Mesoamerica has remained in warmer lowland conditions, Jalisco has climbed to the cooler highlands. The second species, Phaseolus coccineus, prefers cooler temperatures at higher altitudes. Phaseolus dumosus, the final species, acts as a stabilized hybrid marked by intermediate adaptation.

Gepts and his team of researchers collected seeds from 287 bean plants in 10 fields belonging to farmers from the Santa María village, returning to California to plant their findings and study their samples’ genetics. They were curious to determine if farmers’ seed management techniques directed bean seed stocks to the fields in which they were best adapted. They also studied the fields for evidence of gene flow, which can play an important role in crop diversity by introducing new genes to an otherwise uniform crop. The physical separation present between fields in the hilly landscape appears to serve as a barrier to gene flow, confining cultivars to their respective fields. Nevertheless, results from the study show some seeds are slipping through the cracks of these spatial barricades and ending up in unfamiliar territory.

Gepts was particularly impressed with the techniques of one farmer whose two fields, one low- and the other mid-elevation, were used to grow two highly differentiated sub-populations of race Jalisco. The P. Vulgaris born race has ascended the mountains of the region over time, adjusting to the cooler highlands.

But this local grower disregarded years of adaptation and introduced the race to a lower field with higher temperatures, relying on existing variation within the Jalisco field to make the transition. His experiment resulted in the most genetically diverse Jalisco field in the study, highlighting the role, the decisions of farmers play, in crop diversity.

“The farmer distinguished and used intraracial variation to fit those contrasting growing environments, possibly attempting to adapt race Jalisco to warmer environments,” says Gepts, who believes that global climate change is one driving force behind much of the experimentation in the region.

Another is socioeconomic pressure. Some farmers told researchers that they’re focusing on production in warmer, low-elevation fields due to their proximity to the village. Changes in market demand and reduced labor availability may also have notable impacts on the structure of biodiversity of Phaseolus beans in the Sierra Juarez region.

Yet, as society and the environment change and the hilly landscape of this village remains constant, farmers will continue to experiment with the natural adaptations of the Phaseolus bean to better adapt themselves to a changing world. And those decisions in the field may have serious implications on the future of Phaseolus bean diversity.

The full research paper as newly published in Crop Science is available, here:
https://www.crops.org/publications/cs/articles/52/4/1721