Pest-resistant beans to provide US farmers with climate-smart crops with cost benefits

13 Aug 2024 --- Scientists in the US are aiming to reduce farmers’ reliance on pesticides by developing four new long bean varieties that are resistant to the attack of aphids and nematodes that commonly infest the legume. Lowered insecticide use can also allow a “no-spray” labeling for long beans sold at farmers’ markets. 

The aphid-resistant varieties can be substituted for current local lines to minimize insecticide use, and the nematode-resistant varieties can serve as “climate-smart green beans” used in mechanical harvest systems, according to the researchers.

Long beans (Vigna unguiculata subsp. sesquipedalis), also known as asparagus beans or Asian yardlong beans, are grown by Southeast Asian farmers in the Central Valley of California and marketed to Asian immigrant communities across the US.

Though climate-resilient beans can resist high heat and humidity, they are susceptible to attacks from insect pests, which can lead to reduced yield and quality.

The findings are published in the Journal of Plant Registrations.

Impact on farmers

The team found that long beans — grown mostly on small-scale, diversified farms by Southeast Asian refugee Hmong farmers — required the most pesticide of all their crops.

“Local consumers are aware of how much these beans get sprayed, so they’re reluctant to buy the beans. Consequently, the farmers are struggling to sell this product,” says Bao Lam Huynh, first author of the study and a plant geneticist at the University of California, Riverside, which conducted the research.

Root-knot nematodes, commonly found in soils of commercial fields in California and the southern US, cause serious crop losses (Image credit: Bao Lam Huynh/UCR).“It’s very difficult to control aphids, as they can move from crop to crop on diversified farms.”

In California, fresh market long beans are produced for both specialty wholesale distribution and farmers’ markets and are traditionally used in curries, soups and stir-fry dishes. 

“Our idea was to develop resistant varieties not only to minimize the amount of pesticide but to help bring back the market for long beans.”

Meanwhile, some farmers have given up growing long beans due to the aphid pest pressure and concerns about high pesticide use.

Leveraging genetics

The California Department of Food and Agriculture provided the university with funds of over US$400,000 to develop the new varieties over 32 months in collaboration with the University of California’s Cooperative Extension and farmers in Fresno County, California.

The scientists used modern plant breeding protocols and extension activities to develop the resistant lines using sources of natural resistance found in African cowpea germplasm.

“Recurrent parents,” the varieties of long beans used during the study’s initial stage, included Dark Green Local, Light Green Local and Purple Local, procured from a Southeast Asian farmer.

The research yielded three aphid-resistant long bean lines — Dark Green 1994, Light Green 2055 and Purple 2056 and one bush-type long bean line, Bush 2074, for root-knot nematode resistance.

“The nematode-resistant variety can be grown in rotations to benefit other crops, as they could help suppress nematode populations in the fields where they are planted,” explains Huynh.

Aphid infestation is difficult to control, as they can move from crop to crop on diversified farms (Image credit: Lilian Thaoxaochay/UCR).“Without plants like these, farmers would have to use a nematicide to control the worms.”

Cost benefits

According to the study, one of the bean varieties has shorter stems, so it will not require a trellis (wooden or metal bars to support climbing plants) when it grows, allowing it to be prepared for mechanical harvesting. 

Conventional varieties of beans must be picked by hand, one by one, because they require trellises, which makes it difficult for machines to grasp the pods. 

Machine harvesting will further reduce the cost of producing the beans.

What’s next?

The team has multiplied the breeder seed of the three vine-type long bean lines and distributed them to farmers in California. 

“The growers can harvest their own seed for future growing seasons. Long bean is a self-pollinated crop and the released inbred lines would be genetically stable over generations,” states the study.

The researchers further plan to develop varieties resistant to both types of pests and are contacting farmers in the Central Valley in California to introduce them to the new varieties.

By Insha Naureen