Bacteria are more affected by the environment than they are by a plant’s genetics, which plays just a small role
Corn is one of the most important crops worldwide with more than one billion tonnes harvested each year from 13 percent of the world’s arable land. It represents 37 percent of global cereal production.
Recently, the University of Georgia conducted one of the largest leaf microbe studies to date, in which it monitored bacteria on the leaves of 300 different lines of corn.
“I wanted to study how plants can manipulate the organisms living around them,” said Jason Wallace, assistant professor in the Center for Applied Genetic Technologies. “All plants live with huge numbers of microbes on, around, and inside them. Some cause disease but most are harmless or even beneficial. We know very little about how plants deal with this community, so I wanted to see if different corn plants would have different microbes on their leaves, and if we could trace those differences to specific corn genes.”
Wallace wanted to know if corn genes affected bacteria. The goal was to find out not only how crops interact with microbial communities but also whether they can be harnessed to make corn production more sustainable.
The wide diversity of studied corn lines came from a collection of a researcher in North Carolina. While they represent many corn species around the world, most of the material was of corn suited to the environmental conditions in North America. That environmental influence became a critical outcome of the study. In fact, the bacteria were more affected by the environment than they were by the corn’s genetics, which played just a small role.
“I’m a geneticist, so I was always hoping that the corn genetics would play a big role, even though I knew environment would probably also be really strong,” said Wallace. “So, while the environment being important didn’t surprise me, I was a little surprised at just how small a role the plant played in selecting these microbes. Part of it may be that more than one microbe can do the same thing. We saw some evidence that what a microbe can do is probably more important than what they are, which matches what researchers are finding in animals and other plants.”
The influence of the environment in this study included the combined forces of water, wind and soil. But other studies have broken out those elements to explore the influence of component parts.
“One group looked at where the microbes on the leaves came from and found that most of them actually don’t come from the soil around the plant,” he said. “Instead, they blow there from other plants like ones growing in the borders of the field.”
Wallace said that while their research focused on how, or to what degree, the corn affects the microbes, other work done also shows how microbes affect not just corn but other crops.
“Some cause disease, of course, but there’s a lot of work showing that microbes can also help crops grow better. Some microbes help crops withstand drought or heat, get more nutrients from the soil, or just increase yield. In most cases we still don’t know how the partnership works from either the plant or the microbe side, and that’s what my lab is focused on finding out.”
In some respects, corn leaves and bacteria have a symbiotic relationship. But it can be complicated. Wallace said that while some bacteria are passengers along for the ride, others might be a disease in waiting and have not yet gone active.
“The line between these can be hard to draw, since other research shows that microbes can switch roles depending on conditions. For example, bacteria might be harmless or even beneficial when things are going well, but if some trigger happens, for example, the plant gets stressed, it will switch to causing disease.”
In the process of improving plants for better outcomes such as drought, herbicide or pest resistance, breeders often turn to genetic manipulation. But the research suggests that this is perhaps not the best way and Wallace supports management to nurture a corn crop.
“Breeding changes the plant while management changes the environment the plant lives in,” he said. “Simple things like irrigation and fertilizer obviously help plants, and so can things like planting at different times, using cover crops, and treating plants with microbes. It’s hard to give a one-size-fits-all answer for how to improve farm sustainability because what works in one place with one crop could be disastrous somewhere else. I think the key is to keep our minds and options open. Trying to sustainably meet global agriculture demand while facing off against climate and weather extremes is a really hard problem and solving it will require every tool we have.”
Researchers eventually hope to find the plant genes that control the microbe populations living with the plants.
“Since there does not seem to be much of that control on the leaves, we’re starting to look inside the plant itself,” said Wallace. “There’s a whole ecosystem of microbes inside every corn plant, and we don’t really know what most of them are doing. These organisms have an incredibly intimate relationship with the plant, so I think there’s a lot of potential for using them to boost agriculture.”
The research paper, “Quantitative Genetics of the Maize Leaf Microbiome,” was published in Phytobiomes Journal.