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The Unseen Revolution

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Microscopic organisms within plants hold the potential to change agriculture forever
endophyte
This microscopic image shows the presence of an endophyte - in this case, a fungus - living between the cells of a switchgrass stem. The brown and tan areas are the plant cells, while the endophyte stands out as blue lines due to a dye that is used to stain the sample.

"If you want to improve plant efficiency and production, tap into what nature has already done."

Kelly Craven, Ph.D.,
assistant professor

  • Photos

Norman Borlaug saved a billion lives during the 1960s. The Nobel-Prize-winning plant breeder is credited as the father of the Green Revolution, the agricultural renaissance that introduced high-yielding crops and Western society's modern production practices to the starving masses of India, Pakistan and Mexico.

The Green Revolution was based on a simple concept: enhance agricultural production by increasing inputs. By taking improved varieties of crops, then adding substantial amounts of fertilizer and water, agricultural producers in these impoverished countries were able to produce abundant crops.

The concept worked in the 1960s, but half a century later Borlaug's solutions are no longer feasible. The next generation of farmers and ranchers will be required to produce record amounts of food, feed and fiber, as well as potential new renewable energy sources, while using less land and fewer resources. Agricultural producers also face signif icant erosion issues, urban sprawl, a pending pollution explosion and ever-changing geopolitical policies.

Bottom line: A new green revolution is needed.

"It's time to change the formula," said Kelly Craven, Ph.D., mycologist and assistant professor at the Noble Research Institute. "It's time for a green revolution based on a 'low input, high output' formula. We must increase production while using less fertilizer, water and land. This is a fundamental shift in thinking."

Part of the solution to the "fewer resources, increased production" problem will be found in one of nature's smallest groups of organisms - endophytes. In the simplest of terms, endophytes are microscopic organisms like fungi, bacteria or viruses that live in plant tissue. They form symbiotic relationships with their hosts. In exchange for room and board, endophytes impart special abilities to the plant, such as disease and pest resistance, increased drought tolerance or supercharged growth.

Craven and fellow Noble Research Institute mycologist Carolyn Young, Ph.D., seek to understand the power of these natural relationships and harness endophytes' beneficial effects to increase agricultural productivity. "If you want to improve plant efficiency and production, tap into what nature has already done," Craven said. "Our goal is to find the microbes and combine them with new crops to maximize the potential of the symbiosis."

New variety. New opportunity.
More than a decade ago, Noble Research Institute researchers began development of a new type of cool-season perennial grass. The goal was to provide a quality forage for livestock that saved ranchers the expense and time of replanting annual crops like wheat or ryegrasses for grazing. The new forage might also displace a need for costly hay.

As the name implies, cool-season grasses thrive during the cooler months. However, existing commercial varieties could not survive the swelter of southern Oklahoma's blistering summer heat.

Noble researchers soon discovered a variety of tall fescue at one of their research farms that persisted through the summer. Research revealed the grass harbored a fungal endophyte that imparted drought tolerance and persistence to its host. However, the endophyte also produced a compound that caused "fescue toxicosis." The compound (known as an ergot alkaloid) causes cattle to overheat and spend grazing time in water or mud cooling off. "In mild cases, the animal does not eat and simply loses weight, which causes a loss in productivity," Young explained. "In extreme cases, the toxins can lead to the animal's death."

Researchers wanted to keep the positive attributes afforded by the endophyte, but without the devastating side effects. A collaboration with colleagues at AgResearch, an agricultural research and development company in New Zealand, provided a perfect solution - a "novel" endophyte association. By replacing the existing endophyte with the animal-friendly version, the tall fescue managed both to persist through the summer and not cause fescue toxicosis.

The new variety of tall fescue, known as Texoma MaxQ II, is currently in field trials before its scheduled release in 2011. Because these endophytes are found throughout nature, researchers can use them without the lengthy regulatory processes associated with genetically modified organisms or transgenic plants. "All we are doing is capitalizing on naturally occurring relationships between two species," Young said. "Of course, those two species are also benefiting another species - humans."

Texoma MaxQ II and endophyte research could also benefit farmers and ranchers in climate regions dramatically different from the Southern Great Plains. Moving east from Oklahoma, tall fescue remains a staple for agricultural producers. The new variety will help alleviate concerns for ranchers who still use an older version of the grass despite potentially negative side effects from endophytes. For these producers, it will be important to determine the endophyte infection rate - another place Young believes her research could help.

"I envision the day when we can take samples of tall fescue leaf samples in the field that can then be rapidly tested in the laboratory to let the farmer know the endophyte status of his field," Young said. "It will be a quality assurance, providing confidence, knowledge and options to producers with tall fescue."

Beyond Texoma MaxQ II, the Noble Research Institute's grass breeders and endophyte researchers continue to work toward making land in arid climates more productive. Young's focus now shifts to the possible impact of endophytes in summer-dormant varieties, which hold potential for western Oklahoma.

Further research will be required to truly harness the microscopic marvels that are endophytes. The next generation of mycologists will have to drill deeper to clarify their full range of abilities. Young explained that using advanced genomics, scientists are seeking to understand why endophytes are compatible with their hosts and identifying improved endophyte varieties that could far surpass today's already impressive selections.

"We see a sick plant and try to figure out why it is sick, but we don't always look at the healthy plants and wonder why they are healthy," Young said. "Endophytes are hidden treasures, and, until we go hunting, we will not know the full extent of what they can do."

Luckily, Craven is on the hunt just down the hall from Young.

The smallest prey on Earth
Craven is stalking new endophytes, and he's looking in places most ignore. The endophytes found in cool-season grasses, like the tall fescue Young helped develop, are largely derived from the Mediterranean region. These microbes have been well studied with many types identified and their characteristics documented. Craven is delving into warm-season grasses, where the knowledge of these symbioses is slim.

Switchgrass, a warm-season grass native to the Great Plains, has been targeted as a potential bioenergy crop. The grass also holds promise for traditional agriculture - it grows on marginal land and uses less water and fewer inputs than crops such as wheat and corn, and early studies show that it could be part of a year-round forage system. On the downside, the lack of research into switchgrass has left a hole in the knowledge base. On the upside, the Noble Research Institute is located in southern Oklahoma, the center of biodiversity for several warm-season grasses, including switchgrass.

"We want to take advantage of natural symbiotic relationships that occur in switchgrass," Craven said. "This is an amazing plant that takes in so little, but returns so much. We know some of the positive characteristics are likely influenced by endophytes. We need to figure out which ones are playing major roles."

The process is much easier said than done. Craven and his laboratory members collect wild switchgrass (showing no obvious signs of disease) from the extensive grasslands virtually in their backyard, then culture hundreds of fungal and bacterial endophytes found in the roots and shoots. Each strain is evaluated to understand the identity of the endophyte and its putative impact on the plant.

The team tests endophyte impact by introducing each strain into noninfected grass. If the plant shows enhancement in any of a number of growth parameters, then they can assume the endophyte has imparted the effect. While many endophytes offer minimal to moderate enhancements, the team's goal is to find endophytes with dramatic outcomes.

One promising fungal endophyte - Sebacina vermifera - has shown astounding results, enhancing both biomass and drought tolerance. In Noble Research Institute tests, switchgrass with the addition of Sebacina produces over 120 percent more aboveground biomass. Additionally, plants colonized with this Sebacina and exposed to severe drought still produced more biomass than uninfected plants under normal water conditions.

"These results are remarkable and demonstrate what we can hope to achieve," Craven explained.

Since Sebacina is not native to the Great Plains, Craven must find an equivalent strain suited to the region. Other endophytes may prove even more effective under the environmental conditions and soil types of the region. "The goal is to custom design a group of endophytes for a given crop," Craven said. "We can base the endophytes on the crop's deficiencies in a particular ecological habitat."

These deficiencies are being addressed not just by which endophytes are being studied, but by when they are gathered. Collecting throughout the growing season allows Craven to assess how the endophyte community varies throughout the year and which strains predominate in particular seasons. This insight may help agronomists with one of the trickiest issues - switchgrass is difficult to establish. As a perennial, it puts down extensive roots early, while aboveground biomass lags. This allows weeds to choke out the grass and prevent stand establishment.

Craven's team specifically searches for endophytes that might be active or predominant during the early months of the growing season, improving switchgrass's chances of establishment. "These symbioses will help solve some of the initial issues facing switchgrass as well as minimize input costs, such as the need for fertilizer," Craven said. "This will help make biofuel crops more cost-effective and competitive with petroleum."

Another friendly endophyte
While Craven's focus has remained primarily on the endophytic fungi, he has amassed a large collection of endophytic bacteria from native switchgrass. Craven is collaborating with Daniel van der Lelie, Ph.D., from Brookhaven National Laboratory, to evaluate these strains. Research from van der Lelie has already shown that hybrid poplar trees - another promising bioenergy crop - can grow on soils laden with heavy metals or toxic toluene when colonized with a particular strain of bacteria. A similar project is underway to see if bacteria-infected switchgrass can grow on toxic or nutrient-deficient soils.

Craven and fellow Noble Research Institute researcher Michael Udvardi, Ph.D., are investigating the potential of these endophytic bacteria and what role they may play in nitrogen acquisition in switchgrass. Craven also believes that endophytic bacteria might be able to fix nitrogen for the plant much like rhizobia bacteria do in legumes.

"Endophytes will undoubtedly play an increasingly larger role in the low-input age," Craven said. "The Green Revolution saved a billion lives, but required extensive fertilizer inputs which are too expensive and environmentally damaging. We need another revolution; but one that is cheaper and built on a model from nature. These hidden endophytes can help facilitate that. I guess you could say this is an unseen revolution."

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