Endophytes that live in plant cells could confer a host of benefits
February 17, 2015 |By Niina Heikkinen and ClimateWire
Although endophytes live within tissues and are ubiquitous in the plant world, it wasn’t until relatively recently that scientists even knew of their existence.
As scientists seek to make crops resilient against disease and the effects of climate change, they are turning to what may seem like an unlikely champion: fungi.
Specifically, they are studying endophytes, a type of fungus (or bacteria) that lives inside plant tissue and has no apparent negative effects on its hosts. Endophytes do, however, provide important protections to plants, which is why researchers are focusing on how the organisms could be used commercially to improve food security.
Although endophytes live within tissues and are ubiquitous in the plant world, it wasn’t until relatively recently that scientists even knew of their existence, said Brian Murphy, a botanist at Trinity College in Dublin.
Murphy is currently studying how fungal endophytes could be used to protect barley against disease-causing fungi and recently published some promising results in the journal BioControl.
In the study, Murphy and his collaborators cultivated barley seeds that had not been treated with fungicides to see how effective 10 types of fungal endophytes were at preventing or slowing the onset of disease. The seeds were cultivated in a variety of media, and the endophytes were applied either in a cocktail or individually.
They found that the application of specific types of fungal endophytes, isolated from wild barley growing in Dublin, suppressed the development of seedborne infections in barley, without activating the plants’ own defense system. Seeds that were not treated with the fungi developed some of the most devastating varieties of barley pathogens, according to the study.
The type of endophyte that had the greatest ability to suppress pathogen growth was also able to slow the growth of “take-all,” a root disease that also affects wheat and oats. This could mean that endophytes have the capacity to serve as more generalized “bio-control agents,” but researchers won’t know this for sure without further research.
Field tests and a ‘compatibility library’
The study is gaining interest from European agribusiness, and Murphy’s lab is informally working with a major company to make its endophytes commercially available for barley growers. The next step will be to take the research out of the lab and into field trials, which will likely take about three years to complete.
If endophyte use as a disease-fighting agent proves to be viable, it could have wide applicability across the globe, because barley is the fourth most cultivated cereal grain in the world.
“We don’t know how these organisms will behave in a field environment,” Murphy said. “We hope that one or possibly a cocktail of endophytes will be able to help the plants, but we can’t predict outcomes.”
“The other big issue is cost,” Murphy said. If expanding production is more expensive than producing fungicides, commercialization is unlikely. But if development moves forward, endophyte use could reduce long-term costs.
“Because we are coating each seed individually [with endophytes], we might be able to have a self-sustaining population [of fungi] in the soil,” Murphy said.
Out of the 10 fungal endophytes tested, the two best performers came from wild barley growing in sandy, silty soil, with relatively high salinity and low moisture. In the laboratory, endophytes grown in sandy and silty soil cultures performed noticeably better than those cultivated in artificial media.
The research suggests that soil conditions play an important role in endophytes’ ability to suppress infection. It also means that endophytes have specific conditions in which they are the most effective, which has important implications for commercializing their use. Fungi that work well on barley in India wouldn’t necessarily help barley grown in Ireland, and vice versa.
To get around this limitation, Murphy is hoping to one day develop a “compatibility library” to help producers match the right endophyte with their specific growing conditions and crop varieties.
Endophytes aren’t just useful for fighting disease-causing fungi; they also help plants survive a wide variety of environmental stressors. In a separate experiment, Murphy exposed plants to drought, nutrient and pathogen stress to see whether endophytes could help plants survive multiple adverse conditions.
“We found fantastic benefits,” he said. “We hit these plants with them all at the same time, and we really made them suffer. The plants treated with endophytes had six times the survival rate as those without. It’s literally the difference between life and death.”
Fungi help plants use less water
To Murphy, the fungi will be key players in the “green revolution” that will move global agriculture away from heavy reliance on chemical fungicides and fertilizers.
The beginnings of that shift may already be underway. Across the Atlantic, researchers in Seattle are moving forward with commercializing endophytes to make crops more resilient to abiotic stresses that are expected to become more common with climate change.
Rusty Rodriguez, the founder and CEO of Symbiogenics, a nonprofit research corporation, is leading studies on how fungal endophytes could be used to help crops better withstand drought, high temperatures and high soil salinity.
“We found that they can significantly contribute to enhancing the tolerance of these plants,” he said. “The endophytes make them more efficient.”
More efficient plants require less water and nutrients to thrive, reducing the need for chemical fertilizers, as well as the amount of nitrous oxide emissions released from cropland.
Unlike in Murphy’s study, where the endophytes’ ability to fight fungal diseases was connected to the type of media the plant was growing in, Rodriguez said there were no such restrictions for the fungi he used in his studies. However, endophytes do need to be crop-specific.
“We’ve done field testing in lots of different states, in different climates and soil conditions, and remarkably, it didn’t seem to matter,” he said.
So far, the researchers have tested the fungi with a wide range of crops, including barley, wheat, corn and soybeans, as well as sorghum, alfalfa and a number of vegetables.
After about a century of heavy chemical use in agriculture, Rodriguez said, the focus among researchers is shifting.
“The inputs to agriculture are going to be precipitously lower in coming years,” Rodriguez said.
There is also more commercial support for studies like Murphy’s that use fungi instead of chemicals to control plant diseases.
As for his own research, Rodriguez expects that a product line using endophytes, called Bioensure, will be commercially available later this year.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. http://www.eenews.net, 202-628-6500