Some of the most phytophthora-resistance genes used in commercial soybean varieties are becoming less effective, which should prompt growers to keep a closer eye on their soybean fields, says Mark Seamon, research coordinator of the Michigan Soybean Committee.
Seamon recently outlined several challenges and opportunities that emerged from 2020 research funded by the Michigan Soybean Committee.
Plants infected early in the season with the fungus phytophthora may appear as leaf blight, not showing symptoms until later in the season. As plants enter the flowering stage and begin to set pods, symptoms of late-season stem and root rot may develop. Infected older plants show reduced vigor or gradually die over the season. The stems show brown discoloration, which extends upward from below the soil line.
Martin Chilvers, Michigan State University field crops pathologist, has been researching the most common phytophthora-resistance genes (k and c), and in most soils found them to be less effective in protecting against the disease and yield loss.
“Growers need to understand that we can't rely on only variety sensitivity or resistance anymore,” Seamon says. “We need to pay closer attention to our soybeans, and looking for those disease problems in the field will help growers to know how significant this pest is for stand and yield loss.”
Some varieties, he says, have a natural field tolerance that growers may need to rely upon. “Some varieties are able to naturally overcome some infections or withstand disease pressure.”
For farmers using seed treatments, Seamon says to choose wisely. “And for those that don't use seed treatments, watch your fields closer and see if it's an issue. Let's just pay attention a little more because things are changing in the field.”
Soybean cyst nematodes
It’s taken 20 years, but soybean cyst nematodes are adapting and finding ways to feed on what were previously genetically resistant plants. This genetic resistance predominately comes from one source referred to as PI 88788, according to Seamon, who adds that probably 95% of the SCN-resistant varieties available commercially contain that source.
“Growers who have a SCN issue are likely using that source of resistance, which has put the pressure on to develop other forms of resistance” he says.
Several seed companies now have another source of resistance called Peking, which is slightly different.
Marisol Quintanilla, Michigan State University applied nematologist, has done research on nematode populations overcoming one or both of these resistant genes.
“What she's found is PI 88788 is more durable than Peking,” Seamon says. “Nematodes are able to overcome Peking quite a bit faster than PI 88788. So, now that growers have a choice, don't just go to Peking and stay there. Rotate it.
"If you know your nematodes are resistant, or overcoming at PI 88788, throw a Peking in there next time. But the next time you rotate that same field to soybeans, go back to PI 88788 or find a different source. So, there are some management ways around it, it's just a matter of awareness these things are happening.”
Rotation is key, Seamon adds, but acknowledges in years like this where price is pushing soybeans, that’s a tough choice.
Cover crops may have some effect on controlling SCN, Seamon says. Some of this effect may be from general improvement of soil quality and microbial populations, while other research shows potential for a trap crop that may trigger SCN egg hatch but then not allow survival and reproduction of the pest. The Michigan Soybean Committee (MSC) is funding additional projects to learn more about these promising tools.
Additional research is ongoing using seed treatments and their effect on nematodes. “It’s not exactly known yet, but it looks like there could be a benefit. But there sure isn't a silver bullet or a fix for this aggressive pest,” Seamon says.
So the message is, rotate sources of resistance, seed treatments and crops.
New breeding opportunities
Research is ongoing to develop specialty soybeans that will fetch premium pricing. Dechun Wang, Michigan State University soybean breeder, focuses mainly on non-GMO soybeans and niche markets.
“Some of these varieties are being grown, processed and exported to other countries for soybean food uses, including tofu, soy milk and natto, which is a fermented soybean product,” Seamon says. “The soybeans for natto are really tiny — about half the size of a normal soybeans and are being processed in-state.”
Wang continues to work on high-oleic soybeans, which are soybeans bred for better industrial uses, but really aimed at the human consumption market with improved oil health benefits. His research is in non-GMO soybeans, unlike the high-oleic oil mainly produced by the Asgrow and Pioneer brands Plenish and Vistive, respectively.
Wang is working on a non-GMO trifecta — soybeans with high-oleic oil, low-linoleic acid and low-saturated fat. “It's really looking pretty positive, but as with most breeding programs, these things don't happen overnight, and he continues to work on getting performance [yield] from these soybean lines,” Seamon says. “Seed companies, soybean processors and Dr. Wang all know that these specialty varieties need to yield competitively with other commercial soybean varieties for growers to commit acres to producing them. Each generation of breeding gets better than the previous one.”
Food processors such as a potato chip manufacturer, or fast-food fryers who use large quantities of oil, are most interested because of the health benefits, but also because the oil can be used longer and it withstands higher temperatures.
“The MSC board of directors has been intentional in investing grower dollars in helping to answer many production challenges such as these and will continue to support researchers in our mutual quest to make the soybean industry more sustainable and profitable,” Seamon says.