Scientists at Guelph University in Canada have shed light on the partnership between an ancient crop variety and beneficial root-dwelling microbes, which helps protect against a fungal infection that causes billions of dollars’ worth of damage every year. They described the interaction as being similar to an animal’s immune system.
 
The researchers said their discovery of a resistance mechanism to Fusarium graminearum (the fungus that causes fusarium head blight) stands to benefit millions of subsistence farmers in the global south and could pave the way towards developing more natural means of tackling the plant pathogen in a range of crops, including wheat and maize.

Guelph plant agriculture professor Manish Raizada, working alongside a team from the University and other researchers in California, improved understanding of a novel defence mechanism allowing crop plants to work with bacteria called endophytes living in their roots to ward off the fusarium graminearum fungus, which can produce a toxin that sickens people and animals.

The endophyte in question (called M6) lives in the roots of finger millet - a cereal crop grown across Africa and South Asia, which was first domesticated in East Africa over 7,000 years ago.

Finger millet is known to be resistant to fusarium head blight and the North American researchers discovered that, when the M6 microbes sense the fungus near plant roots, they enter the soil and multiply to millions of cells that form a protective barrier on the surface of the plants’ roots. In turn, the plant’s root hairs grow to many times their normal length. Like layers in lasagna, the root hairs and the bacterial cells form a dense mat that then traps the fungus.

The natural products of the bacteria then kill the fungus.

Prof Raizada said, “This appears to be a new defence mechanism for plants.” He said the process bears similarities to the human immune system, with immobile plant cells “recruiting” mobile microbes to seek out and destroy pathogens.

Prof Raizada and his colleagues believe that the process developed as part of an evolutionary ‘arms race’ in the African ancestors of finger millet and Fusarium. The fungus can make an antibiotic against M6 to which the bacterium has in turn developed resistance, the professor said.

“We think subsistence farmers in East Africa over generations may have selected for this special microbe through breeding,” he added.

The M6 microbe is being tested in Canadian wheat trials, to see whether it can confer resistance to other crops, and the Guelph team has since discovered it offers protection against other fungal pathogens.

Prof Raizada said the finding shows the importance of indigenous farming knowledge and practices. “These crops should be explored and valued,” he noted.