Gene may aid high-yield, high-protein soybeans

Soybean crossing plots from trials in Urbana, Ill.

High protein levels negatively correlated to high yields in soybeans.

Leftovers can be valuable, like when soybean seed is crushed and the oil is extracted, what’s left is soybean meal, a source of high-quality protein.

Globally, close to 98% of soybean meal produced is used in animal feed. The U.N. Food & Agriculture Organization calls it “the most important and preferred source of high-quality vegetable protein for animal feed,” according to an announcement from the Crop Science Society of America.

However, soybean growers face a challenge. It has proved difficult to develop soybean varieties with both high protein levels and high yields. These two characteristics are negatively correlated: when soybean yields are high, protein levels tend to decrease, and vice versa.

University of Illinois plant breeder Brian Diers and colleagues addressed this problem in a new study. Their initial results suggest that it might be possible to breed soybeans with higher protein concentration without significantly decreasing yields.

“Growers are typically paid based on the weight of soybeans they deliver to buyers,” Diers said. “Therefore, growers decide which varieties of soybean to grow based primarily on yields.”

If high-protein varieties of soybeans have relatively low yields, they may not be chosen by growers, Diers said.

In this study, the researchers tested a gene that increases protein by breeding it into two different varieties of soybeans. The results were promising. Plants of both varieties with the high-protein gene had increased protein concentration and did not show a significant decrease in yields.

“The study has also increased our understanding of the genetics of protein concentration in soybeans,” Diers said. “That’s important because soybean protein concentration is impacted by many genes.”

These genes are spread across different locations in the soybean DNA. Different versions of genes at each location can lead to higher or lower protein concentrations in soybeans.

The researchers focused on a gene located on chromosome 15, which was previously shown to affect protein concentration. “There hasn’t been research conducted on how this gene impacts agronomic traits like yield,” Diers said.

The researchers developed experimental lines with and without the high-protein gene by breeding the gene into two varieties of soybean and testing the lines for both protein concentration and yield.

“We found that this gene on chromosome 15 consistently increased protein concentration,” Diers said. The gene increased the protein concentration between 8 g and 14 g/kg of soybeans. “This gene could be a good choice for breeders to use when they want soybeans with higher protein concentration,” he noted.

The researchers did see a decrease in seed oil concentration resulting from the gene. However, they did not observe a significant reduction in yield. That’s in contrast to the effect of a gene on chromosome 20 that increased protein concentration but also significantly decreased yields in soybean varieties.

“We did observe a negative yield trend, but it was not statistically significant,” Diers said.

The gene was tested by breeding it into two varieties, which matters because “genes need to be evaluated across different varieties,” Diers noted. “Sometimes, genes only work in some varieties and not others.” It’s important for breeders to have this information to avoid surprises.

High-protein, high-yield varieties of soybeans would be attractive for growers and end users. The protein in soybean meal is considered high quality because it is composed of a fairly well-balanced set of amino acids.

Diers is now working on generating a more detailed map of chromosome 15. A more precise genetic map could help breeders generate other high-protein varieties of soybeans.