The surprising plant-fungi relationship that could help feed us, even as the world heats up

Aug 9, 2017 /

How can you protect crops against global warming? One answer: find the secrets of plants that already thrive in the most punishing climates, says microbiologist Rusty Rodriguez.

When we visualize how climate change will affect our world, many of us picture melting glaciers, waterlogged streets, blistering heat, dried-up lakes and reservoirs, and parched plant life. What may not jump to mind at first are empty refrigerators and dinner tables. But as temperatures rise and extreme weather events like hurricanes and floods become more common, worldwide crop yields are expected to diminish. The Intergovernmental Panel on Climate Change believes that the risk of hunger and malnutrition worldwide could increase by as much as 20 percent by 2050, and developing countries are believed to be especially vulnerable. As humanity scrambles for ways to adapt, scientists are looking for ways to protect the future of food. Seattle-based microbiologist Rusty Rodriguez (TEDxRainier Talk: Unlocking the power of symbiosis in a warming world) believes one possible solution might be to leverage an ancient cooperative relationship between fungi and plants.

A microbiologist responds to the threat of climate change. In the 1990s, Rodriguez was working as a scientist at the US Fish and Wildlife Service in Seattle when he realized that fungi might play a significant role in a warming world. The scientific community was becoming more aware of the wide-ranging effects of climate change, and Rodriguez worried about the plant species that might go extinct in hotter conditions. “Climate change is going to eat our lunch,” he recalls thinking, “and we have no mitigation strategies.”

In search of plants that thrive above 120F. Rodriguez knew that some plants were already growing under hot, harsh conditions. To find out how they did it, he and geneticist Regina Redman (then a colleague, now his wife) went to Yellowstone National Park in the western US, where geothermal soils can reach temperatures up to 155 F (65 C). “You could slow-cook a turkey in these areas!” he says. But some plants flourish in these heated soils, including panic grass. Rodriguez and researchers took some 200 different samples of panic grass from the park and studied them under a microscope, and they found one notable thing: all the plant samples hosted the same fungus.

Fungus so small they fit between the cells in a plant. The microscopic fungus curvularia protuberata was found growing in the spaces between the plant cells. In the lab, Redman and Rodriguez grew two groups of panic grass: ones with the fungus and ones without. To mimic the stressors of Yellowstone, they exposed both sets to soil that fluctuated between daytime temperatures of 155 F and nighttime temperatures of 99 F. The fungus-free plants died after a single day — and after 10 days, the fungus-infested plants were still going strong.

Symbiotic plant-fungi relationships allow both to thrive against the odds. Inspired by their findings, Redman and Rodriguez began looking at other hardy plants: grasses in the salty dunes of coastal Washington, sagebrush in the Utah high desert, plants in volcanic soils in Costa Rica, even mosses from the slopes of Mt. Everest. They found each plant cell was dominated by a particular strain of fungus, suggesting the fungus was helping its host offset the presence of particular stressors, which included salinity, heat, aridity or cold. “These plants were no more adapted to those stressors than your average garden plant, but they had adapted by forming symbiotic associations with the microscopic fungi that lived inside them,” says Rodriguez.

Certain fungi seem to prevent stressed plants from going into panic mode. When a plant receives less water or more heat than it typically requires, its metabolism goes haywire and it expends increased amounts of energy to survive. Most plants under stress also produce more oxidative chemicals, which are lethal to them in high doses. Redman and Rodriguez are still trying to understand the exact mechanism behind stress resistance, but they theorize that certain fungi help plants handle stressors with greater equanimity — with them, their metabolism, although it slows down, does so in a more coordinated way, and their production of oxidative chemicals doesn’t spike. The result is steadier growth despite extreme conditions.

The researchers realized a potential use for superpower-conferring fungi: crops. They sprayed different agricultural plants with fungi and subjected them to stressed conditions in their lab — and found they still grew. “Some fungi have the ability to form symbiotic associations with plants that are genetically distant from the species they were discovered in,” says Rodriguez. Based on their findings, he and Redman formed a company, Adaptive Symbiotic Technologies, as well as the nonprofit Symbiogenics to develop products for the developing world. They’ve created a cocktail that contains 3 to 6 fungi (depending on the crop) in a water-based solution that is sprayed on seeds before planting; as the plant grows, the fungi grow between the plant’s cells. And just as one fungal strain allowed sagebrush to survive in the desert but a different one enabled panic grass to grow in super-hot soil, the mixture relies on a combination of fungi imparting resistance to an array of stressors. Because the fungi don’t grow in the part of the plant that will be harvested and consumed, humans won’t end up eating it. (However, the company has fed symbiotic plants to rats, and the fungi appear to pass safely through their digestive systems.) To avoid the prospect of contamination, the fungi strains die if they spread into the soil. Rather than being genetically modified, the fungi have been selectively bred for certain qualities (e.g., not growing in the “fruit” part of the plant).

The spray has led to promising crop increases in a test case in India. The pair recently worked with growers from a village in the Indian state of Rajasthan. There, farmers coax pearl millet and mung beans from their hot, dry soils, watered by torrential monsoon rains. In the spring of 2016, 96 farmers sprayed 1,300 kilograms of seed. That fall, the average yield difference between sprayed and unsprayed pearl millet was 29 percent; for mung beans, it was 59 percent. “In the US, a significant increase in yield is considered 2 percent,” says Rodriguez. “And these increases happened without requiring any additional land, fertilizer, labor or water.” Redman and Rodriguez have just returned from a second trip to India, where they’ve treated 6,000 kilograms of seed for more than 300 farmers. Testing is now underway in the US, Argentina, Brazil, Peru, Uruguay, Australia and Mauritius on crops including corn, soy, wheat, rice, cotton, beans, peas, lentils and sorghum. These experiments will not only assess the efficacy of the cocktail with a variety of crops in a variety of climates but also generate the data that’s needed to receive regulatory approval in these countries.

It’s feared that climate change will have cascading effects on farmers’ lives — with greater amounts of money being put into producing smaller yields and smaller profits. With the Rajasthani farmers, for example, decreased harvests meant they spent more money buying seed to plant. Rodriguez is hopeful that symbiotic products could have cascading effects in a positive direction: farmers should have more crops to sell, so there will be less seed to buy and more money to spend on other things. After devoting years of research and work to exploring the plant-fungi relationship, Rodriguez wants to emphasize a bigger takeaway, one that could apply to how we deal with other serious challenges. As he says, “There are truly profound accomplishments that we can achieve through cooperation.”