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Research shows that microbes play a vital role in boosting the vigor of hybrid corn

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LAWRENCE – A new article published in the Proceedings of the National Academy of Sciences gives new details and a new understanding of growing corn, one of the largest cash crops in the United States.

Research by a team from the University of Kansas centers on “hybrid vigor,” also known as “heterosis,” a well-known phenomenon where crosses between inbred lines of corn and other crops produce offspring that outperform their parents in yield, drought resistance, and other desirable qualities. Yet the mechanisms underlying heterosis are poorly understood despite more than a century of intensive research.

New research from PNAS examines the relationship between heterosis and soil microbes, showing, in most cases, heterosis is facilitated by a microbial community.

“Hybrid vigor is very important in agriculture because one of the reasons for the sharp increase in crop productivity over the past decades has been the use of hybrid cultivars, which tend to be much more productive and higher. stronger and healthier than inbred cultivars, ”said senior author Maggie Wagner, associate scientist at the Kansas Biological Survey & Center for Ecological Research and assistant professor in the Department of Ecology and Evolutionary Biology at KU. “Despite the importance of this point, we still don’t understand why hybrids are so superior to inbreds. The focus has been on the genetics of hybrid vigor, which makes sense as hybridization is a genetic process – but there is some evidence that the environment is also important in affecting the strength of hybrid vigor. In this article, we have shown that soil-living microbes are one of the environmental factors that have a really big effect on the vigor of hybrids.

In a series of experiments, Wagner and his coauthors found that in most cases, inbred parental lines and hybrid crosses functioned the same under sterile conditions, without the presence of microbes – but heterosis “can be restored by inoculation with a simple community of seven bacterial strains.” Researchers found the same results for seedlings inoculated with “autoclaved soil sludge versus live sludge in a growth chamber and for crop plants in steamed or fumigated soil compared to untreated soil in the field ”.

Wagner’s co-authors at KU were Kayla Clouse and Laura Phillips. The other co-authors were Clara Tang, Fernanda Salvato, Alexandria Bartlett, Simina Vintila, Manuel Kleiner, Mark Hoffmann, Shannon Sermons, and Peter Balint-Kurti at North Carolina State University. Sermons and Balint-Kurti also work with the US Department of Agriculture.

“In the lab experiments, we basically grew the plants in plastic bags in order to provide them with a completely sterile environment,” Wagner said. “It gave us complete control over which microbes, if any, interacted with the plants. So it’s just a little bit of basic microbiology, with a new kind of growing environment. But then, in the field, we tried several different approaches to sterilize the soil, including steam fumigation, which is often used, especially in the production of fruits and vegetables. It’s not really generally used for growing corn, but for this experiment it made sense that we would. And we also tried chemical fumigants and got similar results with all of these methods. “

In the soil vaporization experiment at the KU field station – which temporarily kills or reduces microbes – researchers found that vaporization “increased rather than decreased heterosis, indicating that the direction of the effect depends on the composition of the community, the environment or both “.

“It’s complicated and we don’t quite understand what’s going on yet,” Wagner said. “The first three experiments all showed the exact same direction of the effect. But then, for the fourth experiment, we again found that the microbes were influencing heterosis but it was in the opposite direction, where the hybrid had a more positive reaction to the sterile conditions. We believe this could simply be due to something peculiar to the soil microbial community for this experiment, but we’re not sure yet. “

The new paper is to be followed by research in a similar vein supported by a new $ 900,000 grant from the National Science Foundation involving much of the same staff, with Wagner acting as one of the lead investigators.

Grant work will follow three lines of investigation: testing a range of microbes for their ability to stimulate hybrid vigor in corn; find genetic variants and regions of the corn genome that respond to soil microbes; and researching how microbes behave in the roots of inbred and hybrid corn at the molecular level. Investigators hope their work could lead to better farming and conservation techniques.

“We have this very basic observation of microbes affecting hybrid vigor, but we couldn’t follow through without funding – this grant is going to advance the same line of research,” Wagner said. “My collaborators are Manuel Kleiner from NC State, who is an expert in metaproteomics, which is a means of measuring the protein expression of microbes inside the roots of plants. We hope to learn more about how hybrids and inbreds interact differently with microbes, perhaps by influencing the behavior of microbes. Our other contributor is Peter Balint-Kurti from the USDA. He is an expert on the maize immune system and the genetic bases of disease resistance, so he will map certain genes linked to the responses of hybrids to microbes. Here in Kansas, a graduate student from my lab, Kayla Clouse, will examine some of the larger patterns of this phenomenon – for example, we don’t yet know if all corn hybrids will respond to microbes the same. So far we’ve only confirmed this in a hybrid, so we need to determine how generalizable it is – and we also hope to understand what in the microbial community may affect this response in either direction. Much of his future thesis work will be related to this project.

Work under the NSF grant will continue until 2024.

Top photo: Peter Balint-Kurti takes a sample from a corn plant grown in fumigated agricultural soil in Clayton, North Carolina. Credit: Shannon Sermons.
Photo top right: Young corn plants growing under sterile laboratory conditions. Credit: Fernanda Salvato.
photo bottom right: A team member measures the height of a corn plant grown in fumigated agricultural soil. Credit: Shannon Sermons.

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