AGRO ECOLOGY
New genetic vulnerability to herbicide found in nearly 50 sweet and field corn lines
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RESEARCHERS FROM USDA AGRICULTURAL RESEARCH SERVICE, UNIVERSITY OF ILLINOIS, AND THE PRIVATE SECTOR DISCUSS THE FIRST PUBLIC REPORT OF SEVERE TOLPYRALATE SENSITIVITY IN CORN.
view moreCREDIT: PAVLE PAVLOVIC
URBANA, Ill. — When a sweet corn breeder reached out in 2021 to report severe injury from the herbicide tolpyralate, Marty Williams hoped it was a fluke isolated to a single inbred line. But two years later, after methodical field, greenhouse, and genetic testing, his new Pest Management Science study not only confirms sensitivity to tolpyralate in 49 sweet corn and field corn lines, but also reveals a new genetic vulnerability that may affect corn more generally.
Tolpyralate is a relatively new HPPD-inhibiting herbicide labeled for all types of corn. Typically, corn detoxifies HPPD-inhibitors before they can cause injury, through expression of the Nsf1 gene. Corn lines with mutant nsf1 alleles can show sensitivity to HPPD-inhibitors, but that wasn’t the case with tolpyralate in the lines Williams tested. Instead, his study showed tolypyralate sensitivity is related to a different gene entirely, explaining why sensitivity was neither expected nor caught during the breeding process.
“Cross-sensitivity to multiple postemergence herbicides, all linked to mutant nsf1 alleles, has been understood for years. Breeders typically screen with a product like nicosulfuron, an ALS-inhibitor, because it'll identify (i.e., kill) any inbreds that aren’t tolerant to a wide variety of herbicides, including most HPPD-inhibitors,” said Williams, an ecologist with USDA’s Agricultural Research Service and affiliate professor in the Department of Crop Sciences, part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at the University of Illinois Urbana-Champaign.
The original sweet corn line from 2021 had been screened with nicosulfuron, showing no injury and indicating the Nsf1 gene was doing its job. Expecting the same result with tolpyralate was reasonable, since no one had reported major crop injury from the new herbicide. So, when tolpyralate injury reared its head, the breeder was baffled.
The unusual case led Williams’ team to start hunting for bleached-white corn — the telltale sign of HPPD-inhibitor injury — around the U. of I. farms.
They didn’t have to hunt long.
Here and there, among strapping green corn rows, were stunted, white stragglers. The team contacted the researchers running trials around the farms to find out what had been sprayed. Tolpyralate, every time.
Faced with a phenomenon that looked less and less like a fluke, Williams’ crew embarked on field and greenhouse trials to determine just how widespread tolpyralate sensitivity was. Having easy access to a sweet corn diversity panel, they focused mostly on that group. But they also tested a narrow panel of field corn genotypes.
From the modest screening, the team documented 49 sweet corn (43) and field corn (6) inbreds that suffered moderate to severe injury from tolpyralate. Importantly, the source of the sugary enhancer gene in sweet corn, a parent line for many sweet corn hybrids, was among the most sensitive genotypes, suggesting sensitivity could be even more widespread.
Interestingly, injury was far worse with the addition of atrazine and herbicide adjuvants commonly co-applied with HPPD-inhibitors.
“When we applied pure tolpyralate to the sensitive sweet corn inbred, the crop looked fine,” Williams said. “But when we added adjuvants recommended by the herbicide label — crop oil or methylated seed oil —we got a severe bleaching response. And when we also included atrazine, which is common with HPPD-inhibitors, plant mortality was rapid.”
Williams clarified it’s not feasible to just remove the adjuvants from the tank. They improve herbicide uptake by weeds and are essential for successful weed control.
“Tolpyralate has agronomic advantages, but obviously it will have limited utility if it harms the crop,” Williams said.
With mounting evidence suggesting nsf1 wasn’t to blame for tolpyralate sensitivity, the team then mapped the genome to find the culprit.
“Using the original sensitive sweet corn line to map the trait, we narrowed it down to the region on chromosome 5 near Nsf1. But it’s not Nsf1, and there's nothing obvious in the genomic region we identified that easily explains tolpyralate sensitivity. So, while we've mapped the trait, the physiological mechanism remains elusive.”
Williams notes that more research is needed to get to the bottom of tolpyralate sensitivity, both in terms of the physiological mechanism and how widespread the trait might be in all types of corn. He said there’s potential to develop molecular markers that can identify sensitive corn lines, which would be useful in improving tolerance to tolpyralate.
For now, he wants to raise awareness among corn breeders, growers, and chemical companies working on the next generation of HPPD-inhibitors, especially since this is the first incidence of a genetic vulnerability to a corn herbicide documented in over three decades.
“What we have learned from this research may be helpful beyond tolpyralate itself, since several new HPPD-inhibitors derived from the same chemical structure are being developed,” Williams said. “If we can avoid additional problems in the future, let's do it now."
The study, “First report of severe tolpyralate sensitivity in corn (Zea mays) discovers a novel genetic factor conferring crop response to an herbicide,” is published in Pest Management Science [DOI: 10.1002/ps.7896]. Authors include Marty Williams, Nicholas Hausman, Ana Saballos, Christopher Landau, Matthew Brooks, Pat Flannery, William Tracy, and Charlie Thompson.
JOURNAL
Pest Management Science
Study: Extreme rainfall increases ag nutrient runoff, conservation strategies can help
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THAWING CAUSED BY WARM WINTER WEATHER INCREASES MANURE RUNOFF FROM FIELDS – LEADING TO HIGHER PHOSPHORUS CONTENT IN WISCONSIN LAKES.
view moreCREDIT: HERB GAM, USGS.
URBANA, Ill. – Nutrient runoff from agricultural production is a significant source of water pollution in the U.S., and climate change that produces extreme weather events is likely to exacerbate the problem. A new study from the University of Illinois Urbana-Champaign looks at how extreme rainfall impacts runoff and suggests possible mitigation strategies.
“We look at more than a decade of precipitation events in the state of Wisconsin and quantify the increase in nutrient runoff right around the event and at the end of the growing season. Climate models predict that we’ll continue to see an increase in extreme events, and our works speaks to the challenging relationship between nutrient use and water quality,” said Marin Skidmore, assistant professor in the Department of Agricultural and Consumer Economics, part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at U. of I. Skidmore is lead author of the study with coauthors Jeremy Foltz from University of Wisconsin-Madison and Tihitina Andarge from the University of Massachusetts-Amherst.
“Our focus on a single state allows us to accurately measure farm locations and practices, while keeping statewide regulation constant, in a way that would be difficult in a national study,” Skidmore added.
Livestock manure and crop fertilizer are major causes of nonpoint source pollution from agriculture. Wisconsin has a large dairy industry, where most farms are below the federal definition of concentrated animal feeding operations (CAFOs) and therefore not regulated under the Clean Water Act. Instead, they are subject to a patchwork of local regulations.
The researchers studied water quality across nearly 50 watersheds in Wisconsin from 2008 to 2020. They correlated ammonia and phosphorus concentration data from the Water Quality Portal with the location of livestock farms and crop acreages, and they determined nutrient levels after ½ inch, 1 inch, and 2 inches of rainfall.
They found spikes in nutrient concentrations immediately after extreme precipitation events, and the effect increased with the amount of precipitation. For example, within five days of an inch of precipitation, ammonia was 49% higher and phosphorus was 24% higher. If there was at least one day in a month with over an inch of precipitation, monthly ammonia was 28% higher and monthly phosphorus was 15% higher.
“We observe a significant interaction between rainfall, agricultural production, and runoff. It is not just a short-term spike in nutrient levels; at the end of the season, we still see persistent increases in phosphorus and ammonia attributed to those extreme precipitation events months earlier,” Skidmore stated.
However, the researchers found that agricultural management practices can help mitigate the effects.
“Our results show that cover crops planted in the winter can lower the amount of nutrients in the water. Areas with cover crops have significantly lower spikes in ammonia and phosphorus, and the effect persists until the end of the growing season. We already know cover crops are great for soils and nutrient management, but this is additional empirical evidence showing that cover crops are climate-smart practices that can help agriculture be resilient into the future,” Skidmore said.
The researchers also observed the presence of legacy nutrients, which are left behind from agricultural practices decades or even centuries ago.
“There is a direct impact of extreme precipitation on runoff that is unexplained by current activities. We attribute this to sedimented nutrients that remain in the soil from previous activities,” Skidmore noted. “One of the best ways to deal with legacy nutrients is to ensure soils are healthy. By preventing soil erosion, you keep the legacy nutrients in the soil and out of surface water. These findings further support the use of management practices such as conservation tillage, vegetative buffer strips, and cover crops.”
Wisconsin watersheds feed into North America's two largest river systems, the Mississippi and Great Lakes/St. Lawrence. Nutrient pollution can have acute local impacts, such as green algal blooms, which can be toxic to humans and animals. If people can’t enjoy recreational activities like swimming or fishing, it leads to losses for local economies. Furthermore, downstream impacts continue along the Mississippi River into the Gulf of Mexico where nutrients contribute to a growing dead zone.
Finding solutions to dealing with nutrient pollution benefits the environment and society in general, Skidmore noted.
“Conservation strategies are not necessarily cost-effective for producers, so we must ensure there are policies in place to support their implementation. As we're approaching the next Farm Bill, there are discussions around how to allocate funds from the Inflation Reduction Act for climate-smart and conservation ag practices. It’s important that such practices continue to receive funding so farmers can facilitate those benefits for all of us,” she concluded.
The paper, “The impact of extreme precipitation on nutrient runoff,” is published in the Journal of the Agricultural and Applied Economics Association [doi.org/10.1002/jaa2.90]. Authors are Marin Skidmore, Tihitina Andarge, and Jeremy Foltz. Skidmore and Foltz received funding from the Wisconsin Dairy Innovation Hub and Andarge was supported by USDA National Institute of Food and Agriculture Grant No. 2022-67023-36377.
JOURNAL
Journal of the Agricultural and Applied Economics Association
ARTICLE TITLE
The impact of extreme precipitation on nutrient runoff
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