Eggs within a dead female soybean cyst nematode can survive in the soil for years. (Photo: Iowa State University)

Nematologists eager to study a new soybean variety with SCN resistance

A new soybean variety with resistance to soybean cyst nematode (SCN) derived from the breeding line PI 89772 is being released by Syngenta in small quantities in 2020. Syngenta is sharing seed with university researchers and farm cooperators now, and full commercial launch is expected in 2021. “We’re excited about a new soybean variety with a source of SCN resistance derived from breeding lines other than PI 88788 and Peking,” said Melissa Mitchum, molecular nematologist at the University of Georgia and co-leader of The SCN Coalition. “If the new variety has the right combination of resistance genes, it could offer a novel mode of action that shifts SCN populations in a different direction than the PI 88788 breeding line and possibly the Peking breeding line, too.”

USDA researchers originally discovered PI 89772 on an expedition in China back in 1930. Ninety years later, and after nearly 25 years of work by breeder Jose Aponte, Syngenta is releasing the variety under two brand names: Golden Harvest GH2329X and NK Brand S23-G5X. It is a Maturity Group 2.3 bean with SCN resistance, good SDS tolerance and the Roundup Ready 2 Xtend trait.

Melissa Mitchum,molecular nematologist at the University of Georgia

Mitchum says earlier research by herself and her predecessors at the University Missouri showed promise for PI 89772 resistance. “It showed that if you have an SCN population that’s highly virulent (able to feed and reproduce) on PI 88788, the population drops significantly when you test it on PI 89772. We showed a similar response to the breeding line PI 90763. We are looking more at this in collaboration with soybean breeders.”

Including PI 89772 in checkoff-funded research, these findings dovetail with a research project funded by the soybean checkoff via the North Central Soybean Research Program (NCSRP) and headed by Mitchum. For the project, Mitchum and her co-principal investigators are working to accomplish a number of things. They plan to diversify the genetic base of SCN resistance in soybean. They are working to identify SCN virulence genes to better understand how the nematode adapts to reproduce on resistant varieties. They will also determine what combinations of resistance genes would be beneficial in rotations to enhance the durability of SCN resistance.

“We just finished the first year of a three-year microplot field study,” Mitchum said. “We’re planting different SCN-resistance gene stacks or pyramids in different rotations, including PI 90763. We’re looking at SCN population densities, how they change based on the different SCN genetic resistance being deployed and how the HG type of the SCN populations shifts over time.”

Mitchum is hoping to include Syngenta’s variety carrying PI 89772-type SCN resistance in 2020 trials. Alexandra Ostezan, a graduate student working with soybean breeder Zenglu Li and Mitchum at the University of Georgia, is already at work mapping the resistance genes in PI 89772. Pawan Basnet, a graduate student working with Mitchum and soybean breeder Andrew Scaboo at the University of Missouri, is at work mapping the resistance genes in PI 90763. Both checkoff-funded research projects are supported by the United Soybean Board.

There is ongoing testing PI 89772 in farmers’ fields. Nicole Deitloff, a graduate student at Iowa State University, who is also an NK seed sales representative, will be testing Syngenta’s new variety on four Minnesota farms in 2020. She’ll be comparing it to varieties with PI Ohio Field Leader Soybean Conservation Practices88788 and Peking SCN resistance, with and without Saltro seed treatment.
SCN Coalition co-leader Greg Tylka, a nematologist at Iowa State University and Deitloff’s graduate program advisor, encourages soybean growers to try the new Syngenta variety if they can get their hands on it.

“We know SCN is chewing up PI 88788 resistance,” Tylka said.

Aponte, the Syngenta soybean breeder who’s been working with PI 89772, says it’s been a long journey when asked how a new resistance source came to market.

“We’ve been collaborating with USDA and the University of Illinois for years, looking for sources of resistance other than PI 88788, which is 99% of what is being sold today,” Aponte.

Because the original source of PI 89772 was from USDA germ plasm, the researchers initially had agronomic issues which they had to overcome.

“First we needed to breed the performance and defensive packages into conventional soybean lines, then we had to transition it to herbicide-tolerant lines, first Roundup Ready 2 lines, then Xtend, Enlist E3 and ultimately XtendFlex,” said Aponte. “It takes time to develop a new herbicide trait, then move the other agronomic traits into a good bean. But SCN is a growing problem, and we want to be part of the solution.”

Mitchum’s ultimate goal with the NCSRP project includes “marrying our knowledge of resistance with our knowledge of different SCN populations so we can offer farmers prescriptive SCN management. Ultimately, we want to develop a rapid test to determine the SCN population in a soybean grower’s field that will help determine which genetic resistance to plant and which resistance rotation strategy to follow. We hope to make this a reality.”

The SCN Coalition is a public/checkoff/private partnership formed to increase the number of farmers who are actively managing SCN. Our goal is to increase soybean farmers’ profit potential and realize higher yields. Partners in The SCN Coalition include university scientists from 28 states and Ontario, grower checkoff organizations including the North Central Soybean Research Program, United Soybean Board and several state soybean promotion boards, and corporate partners including BASF, Bayer, Growmark, Nufarm, Pioneer, Syngenta, Valent and Winfield United

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