b'Nitrogen-Fixing Corn Hybrids in the U.S. The million (perhaps even billion) dollar question is whether the weather in U.S. corn-producing states can support future hybrids that can produce and maintain sufficient mucilage to fix signifi-cant amounts of nitrogen. So far, it looks like the answer is yes. You need regular rainfall to spur mucilage production, An reports. But even a shower of 5 to 10 minutes is enough. The gel is secreted within 30 minutes of rain and stays for two or three days with good humidity. Weve found the average frequency of rain is sufficient in the corn belt, in Georgia, Wisconsin and Florida. Twice a week is really good, but we are getting once a week here in Wisconsin and we are getting good gel production.The team is also looking at what extent humidity affects the number of nodes that have aerial roots and the thickness of these roots, both of which means more gel and more N fixation. Aerial root production only occurs when the plant is large enough. Nitrogen fixation is tricky to determine accurately Photo provided by Jean-Michel Anand there are several methods to do it, all of themvisual selection of the progeny in terms of more roots and thicker with pitfalls. Jean-Michel An roots. So, we have some plots focussed on how traits of Mexican landraces and modern lines integrate, some plots just looking at the trait of aerial root production, and other plots looking at several other things. We have about two acres here and another acre of plots at another UW research station in another region where they can simulate rain with overhead irrigation. Wallace notes that at this point, while the project is at the genetics stage and not yet the breeding stage. Once we know Evaluating Yield Impact of Nitrogen-Fixing Traits how the hybrid crosses behave this summer, we can start build-Another critical question is whether there is a yield cost to theing breeding models. And once more is known about the genes, trait of aerial root production. The team published modellingwe can identify markers and use AI-assisted breeding and avoid data last year showing its likely 4-11% of a plants energy, and atlinkage drag by editing out the bad genes of the landrace. 4%, there is no impact on yield. That includes a very tall height (propensity to lodge) and a But even if there is a yield hit and you lower nitrogen fertilizermaturation of eight months.input costs by even 10%, you will still come out ahead, WallaceDe Leon notes that how the aerial root genes work seems notes. Of course, we need lots of field trial data to find out.to be fairly simple, but even if there are several genes and their This summer, we are comparing hybrid crosses of the Mexicanmechanism is complicated, that will not stop breeding progress. landraces with U.S. Midwest-adapted varieties to siblings withoutThe gene editing revolution is continuing to unfold, she says. the trait and we will have our first dataset on the yield cost of theThe biggest limitation is not with the technology but with public trait, if any. the acceptance and also having the resources. It is fantastic that The U.S.-adapted varieties with which the team is crossingwe have the Wisconsin Crop Innovation Center here, which is the Mexican landraces are available in the public domain. Theydedicated to using gene editing with many crops. The opportuni-were cutting-edge commercial hybrids 20 years ago. De Leonsties are very real. expertise is being harnessed for tasks such as deciding which of these modern hybrids make the most sense to introgresstoPatience and Timeintegrate transfer of the aerial root trait without losing the posi- We need to take our time and manage expectations, An tive traits of modern cultivars, thereby avoiding linkage drag.adds. Expectations are very high. We have to be careful what Jean-Michel has already done some evaluation of this, andwe claim. Nitrogen fixation is tricky to determine accurately and I am helping him with a more systematic and larger evaluation,there are several methods to do it, all of them with pitfalls. There de Leon explains. We are mostly using inbred lines and doingis excitement, there is investment, but we have to be careful not SEPTEMBER 2024SEEDWORLD.COM /39'