The bean weevil is an evil little insect that bores into bean pods to devour the meal, thus leaving a hollow shell. It’s happy eating any type of bean seed.
The larvae bore into the pods and continue feeding until coming out as adults to infect more seeds. They impact beans in the field and beans in storage. Weevil infestations can spread rapidly, infesting large quantities of stored beans within a few months.
Common beans, also known as green beans, French beans and other regional names, are packed with nutrients and protein. They grow in many different environments, help replenish soil nitrogen levels and are a vital crop for food security in many parts of the world. The bean weevil is indeed an evil enemy.
In some areas of the world, farmers treat bean seeds with ash from cooking fires to control weevils. That’s not particularly effective and it’s only possible on a small scale. Suffocating weevils by triple bagging beans in storage is another option, but air tight bags are not always available. Treating seeds with chemicals can be effective but it’s costly and may carry health risks.
With the world trending away from pesticides, especially insecticides, the Legume Innovation Laboratory at Michigan State University decided to fund a plant-breeding project delving into non-chemical methods of weevil control.
Michigan is providing funding and assistance to Kelvin Kamfwa, bean breeder at the University of Zambia. Kamfwa is the lead author of a new study that has narrowed down the genetic locations of several weevil-resistance genes in the common bean. The study confirmed that weevil resistance in beans is genetic. Resistance to weevils can be transferred to bean plants with different seed types and colours.
The study also showed that weevil resistance is inherited separately from seed size. That’s important because earlier studies suggested a relationship between weevil resistance and seed size. If true, that would prevent plant breeders from developing larger-seeded beans with weevil resistance.
“This will allow breeders in different countries to introduce weevil resistance into bean varieties adapted to local conditions,” says Kamfwa.
“Beans with larger seeds are preferred by consumers in several areas of Africa. This means growers will have eager buyers, ensuring the growers’ livelihood. Weevil resistant varieties help in the field and when it’s time to store harvests. They will be able to save seeds for home use or for the next planting season. They can store seeds to sell when prices are more favourable.”
To learn more about the genetics of weevil resistance in common beans, Kamfwa and his colleagues used bean plants derived from an initial mating between a weevil-resistant and a weevil-susceptible variety of common bean. For each bean plant tested, they calculated the percentage of bean seeds damaged by weevils. This measurement provided a quantitative idea of how resistant each bean plant was to weevils. The researchers also sequenced the entire DNA of the bean plants. Then they combined the weevil-resistance measurements with the DNA sequence information.
Next they used statistical analysis to find genetic markers that are more common in the DNA of bean plants resistant to weevils. These genetic signals act like molecular beacons, allowing the researchers to hone in on regions of bean DNA that are important for weevil resistance.
“Using bean plants directly to research weevil resistance can be complicated and time-consuming. Being able to indirectly look for resistance with genetic markers will hasten the breeding process.”
The researchers found three regions of bean DNA important for weevil resistance. One of these regions was known previously, but two regions were new discoveries. Kamfwa intends to develop a genetic marker system that can be widely used by bean breeders around the world, which is why Michigan became involved.
“Ultimately, we hope our findings contribute to food security needs in countries where the common bean is a valuable staple food. Developing bean varieties resistant to the bean weevil is a long-term solution to a very serious problem.”
Kamfwa’s research was made available through the American Society of Agronomy, the Soil Science Society of America and the Crop Science Society of America. Collectively these societies represent more than 12,000 individual members around the world. The scientists’ memberships build collaborating partnerships in agronomy, crops and soils for the advancement of knowledge.