ENDORSED BY ENDORSED BY 58 / SEEDWORLD.COM JUNE 2019 management practices for this pest.” Additional team mem- bers include Brian Diers and Andrew Scaboo, plant breed- ers; Greg Tylka, an Extension field nematologist, Thomas Baum, molecular nematolo- gist, and Andrew Severin and Matt Hudson, both informat- ics specialists to work on the computational side. The project’s objectives are to first understand the genet- ics of the nematode, then understand the genetics of the plant. Finally, the research- ers plan to marry those two objectives to develop new types of genetic resistance and better diagnostic tools to apply resistance more stra- tegically. Mitchum says they also hope to identify genetic vulnerabilities within the nematode that will allow them to engineer novel forms of resistance. “This project is focused on breaking the SCN resist- ance cycle and working with plant breeders to diversify and stack soybean’s genetic resist- ance,” Mitchum says. “Diers’ group has already stacked other types of resistance on top of PI 88788 resistance. “Other breeders are iden- tifying additional sources of new resistance and getting those into varieties.” Nematologists are simul- taneously working with the breeders to put those varie- ties into rotation schemes that would make sense for farmers. The project looks at taking some of these gene stacks breeders have developed and incorporating them into a rotation scheme to see how it impacts nematode popula- tions. The scheme calls on farmers to more strategically rotate resistance to not only preserve the current source but also to better manage virulent nematode populations in the field. Researchers have com- pleted a greenhouse study that rotated Peking resist- ance with the stacked resist- ance Diers developed which includes the wild soybean Glycine soja resistance stacked on top of the PI 88788 resistance. The second phase of this study is a three- year field trial beginning this spring to evaluate what hap- pens when moved to fields in Missouri, Iowa and Illinois. On top of the reference genome, Mitchum’s lab is working to develop a series of adapted nematode popu- lations. One will be highly adapted to the PI 88788 type of resistance, another popula- tion that is highly developed to the Peking-type of resist- ance and another population that is highly adapted to the Glycine soja-type of resist- ance. The team will then sequence the genomes of those populations and com- pare them to a population with very few individuals that can grow on a resistant vari- ety. She hopes to pinpoint the genes in the nematode that allow it to overcome these sources of resistance. Speed Matters Right now, if farmers want to know if they have a nematode population that can overcome a current source of resistance, they must send a soil sample to a lab for an SCN HG type test. It is a labor-intensive analysis that takes a month to complete. With a molecular diagnostic tool, a diagnostic lab might be able to extract the nematode from that soil sample and overnight provide a result as to whether or not the nematode population has adapted to any type of soybean resistance. “We call this precision nematode management,” Mitchum says. “This would allow farmers to have access to different types of genetic resistance and plant varieties that have the most resistance to the nematode population in their field. Maybe a farmer has no SCN presence but if they do get the nematode and they keep planting the same PI 88788 resistance, then we will just be perpetuating the issue.” As new types of soybean resistance are developed, seed companies will need to take up these other types of resistance and bring them to market. Then farmers will need to know how to rotate them strategically to bring their population levels down. “Genetic resistance is farmers’ best tool for manag- ing SCN. It works really well when it works,” Mitchum says. “We need to maintain the cur- rent sources of resistance and breed high-yielding varieties with new sources and deploy them strategically. SW Gary Tylka is an Iowa State University professor of plant pathology and microbiology.