Bringing new food to the table by cultivating a native plant

Climate change, marked by more pronounced weather extremes, has prompted searches for new food crops. Such crops must be able to resist wide temperature variations and alternating periods of drought and floods, and produce high yields. Steven Cannon, a genetics researcher at the USDA-ARS Corn Insects and Crop Genetics Research Unit in Ames, IA, is convinced that a humble, overlooked tuberous legume will be one of those crops.

Researchers holding apios

According to Cannon, whose recent study was published in the February 2015 issue of Crop Science, legumes are attractive as food crops for several reasons. They’re able to convert nitrogen in the air to a form that plants can use directly. This ability reduces dependence on chemical fertilizers and also benefits the soil. “Legumes tend to be unusually nutritious for humans and livestock,” says Cannon, since the nitrogen is typically used to make seeds or other storage tissues that are rich in protein.

Cannon’s crop of choice, Apios americana, was well known to Native Americans and early European settlers. Also called potato bean or groundnut, Apios is a weedy plant with tubers that taste like boiled peanut. “The part of the plant that is eaten is an underground tuber, making it more like Irish potato or sweet potato or cassava,” says Cannon. Nutritionally, Apios resembles common dry beans more closely than starchy tubers. Cannon explains, “Apios has about 16% protein by dry weight, compared with about 4% in potato.”

In many ways, Apios is an ideal food crop. It can be grown as a perennial, tolerates a wide variety of soil conditions—including floods—and has a high yield. Cannon’s study set out to examine how the physical characteristics (phenotype) of Apios changed in relation to the plant’s genetic characteristics (genotype) under various growth conditions.Apios growing in the field

Of several phenotypes that showed high variation, the study focused on the weight of new or “child” tubers. Child tubers are produced along offshoots of the central, or “mother” tuber. During harvest, larger tubers are easier to process and use.

“Based on the results obtained in this study,” Cannon says, “child tuber weight is strongly correlated with yield, and is genetically controlled and is a stable characteristic across environments.”

The study also identified above-ground traits that correlated strongly with below-ground yield. Internode length is the distance between points on a stem from which buds, leaves, or other structures originate. Cannon found that internode length can be used as a selection parameter for high-yielding plants. “[We can] first grow Apios plants in a nursery and then select plantlets with long internodes,” he says. In addition, the study determined that stem diameter and above-ground plant vigor are correlated well with below-ground growth.

These phenotypes, Cannon notes, can be used to study variation across different Apios lines. With further validation, the study’s results will help in early selection of high-performing varieties.

“We have identified nearly eight promising lines that have consistently produced higher yields,” says Cannon.

These lines show great promise for small-scale production and are ideal for farmers with limited resources. Large-scale cultivation, however, will require suitable harvesters, as Apios plants are vigorous vines that require a lot of digging.

Ultimately, Cannon hopes that new Apios cultivars will contribute to increasing crop diversity. He notes that the crop holds particular promise in countries where flooding and protein malnourishment exist.

“Having a wide variety of crops—suited to many different environmental conditions —provides something of a hedge against environmental changes,” says Cannon.

Acceptance of a novel crop requires time and increased public awareness. But the plant’s benefits may mean that healthy and protein-rich Apios dishes will find their way onto the dinner table for future generations to enjoy.