Plant breeding is usually not on most people’s minds when they are playing in the yard with their kids,walking their dog in the park, or hitting a dimpled ball down a fairway. But behind these beautiful lawns, courses, and fields that we all cherish is the science of turfgrass breeding. In a resource-limited future, turfgrasses will need to do more with less, and so today there is a broad effort under way to breed grass that is more sustainable, and thus, truly green.
Turfgrasses are estimated to cover 40 to 50 million acres in the United States, and their benefits are well established. Besides the pleasing aesthetics of a green park-like slope, turfgrasses are very functional plants. Their dense roots absorb rainwater faster than most crop fields and prevent erosion on steep slopes. They produce oxygen, capture carbon dioxide and dust from the atmosphere, and have a cooling effect on the surrounding area.
A 2011 review in the Journal of Public Health found that although evidence of beneficial health effects are weak, most studies generally support the view that green space has beneficial health effects through exercise, psychological impacts, and air quality. And in terms of safety and comfort for sports, grass knows no equal.
Highly maintained and manicured lawns and golf courses have also gained some notoriety in recent years for their impact on the environment. Maintaining that perfect carpet of dark green blades often requires water, fertilizer, pesticides, and frequent mowing—each of which can take their toll on groundwater, wildlife, and energy supplies. A study published in the Journal Environmental Management in 2005 estimated that it could take as much as 700 to 900 L of water per person per day to satisfy the thirst of these plants, which together, make the largest irrigated crop in the country.
In response to tightening potable water supplies, park and golf course managers began to use treated wastewater on the grasses and practice integrated pest management (IPM) to reduce the costs and impact of these lawns. Some golf courses have also converted peripheral lawns to wilder low-input landscaping. But the needs of the turfgrasses in these green spaces have remained amid the changing environmental and economic landscape, so today, there is a focus on breeding current and altogether new turfgrass species to fit a new paradigm of sustainability.
CSSA Member Eric Watkins is an associate professor in the Department of Horticultural Science at the University of Minnesota–Twin Cities and breeds turfgrasses for the cool, northern climate where he is located. One of the things he enjoys about working with turfgrasses is how easy it can be to explain what he does to people.
“I like the fact that everyone knows or uses grass,” he says. “Lawns are a great way to talk about plant biology….When I talk to people about some of the traits that we work on like reduced mowing, it is something that people can easily relate to.”
But people also take turfgrass for granted, according to CSSA member Ambika Chandra, an assistant professor at the Texas A&M AgriLife Research & Extension Center at Dallas, TX, who breeds grasses for warmer, southern climates. “People just look at turf and don’t think a lot about it. It is just something they walk on and play on. In the grand scheme of things, it is not a food or fiber or feed, but it does impact the lives of people in many different ways, including their social, mental, and overall well-being.”
No Miracle Grass
There is no single species of grass that is superior in all environments or uses, so turfgrass breeders work with several different species at a time. “The thing that really intrigues me,” Chandra says, “is the fact that there’s so much diversity in turf. There are more than 40 different species of grass that have applications for turfgrass.” She adds that working with many species can mean working with many breeding systems. “Some are open-pollinated, some are self-pollinated, and some can be apomictic and produce clones of their parents. They tend to be polyploids, which you have to take into account when you set up your crosses.”
Each grass species can have combinations of traits that work well together in one environment, but not another. “No species of turfgrass is going to be a miracle grass,” Chandra says. “Every species has its strengths and weaknesses. Some that you might think are a weakness may be a strength in another environment. You have to consider your environment—where is it going to go? Is it going to be used on home lawns or on putting greens?”
One important trait is the type of photosynthesis that the plant employs. Most species have what is called C3 photosynthesis, where carbon dioxide is absorbed by the enzyme Rubisco directly from the atmosphere when the stomata in the leaves are open and captured in a three-carbon molecule. This simple process is well-suited to cool climates, but under hot temperatures, it is inefficient and can lead to damage as Rubisco can absorb oxygen when the stomata are closed and carbon dioxide is unavailable.
These problems are addressed by C4 photosynthesis, which is an adaptation that uses a second enzyme, PEP carboxylase, to shuttle carbon dioxide into the plant in the form of a four-carbon molecule. C4 plants use water more efficiently, and tend to withstand higher temperatures, but can perform poorly in cold conditions. Thus, cool-season turfgrasses will have C3 photosynthesis, while C4 will be found in warm-season grasses.
Watkins breeds cool-season grasses for his region, such as Kentucky bluegrass, perennial ryegrass, tall fescue, and a few fine fescue species. He is also working on a few new species of grass, such as prairie junegrass, and most of his grass cultivars are intended for home lawns and parks.
Chandra, on the other hand, works primarily with warm-season C4 grasses, such as St. Augustine grass and multiple species of Zoysia grass, but she also works with Texas bluegrass, a cool-season C3 species. “Being a cool-season grass, it is not well adapted to warm climates. This [Texas bluegrass] has been utilized as a forage grass, and our intent is to develop a turf-type grass with interspecific crosses.”
Breeding for Drought, Salinity Tolerence
Each species can also be susceptible to different diseases and pests. These kinds of traits are important to consider for any breeding program, but to address the question of water use in green spaces, a main focus of their breeding programs is in drought and salinity tolerance. It all starts with breeding in the right environment.
“We are in the southern part of the country, very hot and dry,” Chandra says. “One of the unique things about this area is the soil, which has a lot of clay. It takes a long time for the water to get through the soil profile. Some genotypes do better in these types of soils and some don’t.” However, a consistent environment for selection each year is not always easy to obtain, she adds. “It is very much controlled by Mother Nature.”
In Minnesota, Watkins has to generate some of these environments artificially. “When we select for better performance under drought, we grow them under a rainout shelter and we limit the nitrogen inputs—we mainly just maintain our breeding plots in a way that is similar for the environment the grass will be grown in.”
While breeding for drought tolerance, both Chandra and Watkins have to keep in mind how the cultivars perform during the winter. Chandra says that she has had some severe winters where a lot of their material was lost. Watkins adds, “If you think about a home lawn grass in Minnesota, one of the most important things is that they would have to survive the winter. Most species will typically survive winter, but this winter, a couple species didn’t do very well.” To manage winter selection, he says “we’ve come up with some ways to do controlled freezing in the lab, but winter hardiness is still a challenge.”
Between the warm South and the cool North lies the transition zone, which can have both the extremes of the North and South. “The transition zone is really difficult to breed for,” Chandra says. “Some species don’t have cold tolerance, and some don’t have heat tolerance.” To bridge this gap, she is working on warm-season grasses that can also be cold tolerant.
Soil salinity is also an important issue that has captured the attention of these two breeders. As golf courses and parks are watered with treated wastewater, and less freshwater is used during dry conditions, salt levels in the soil can build up, impacting the soil structure and hindering the growth of the plants. Chandra explains that there are two important mechanisms that turfgrasses use to withstand excess salt in the soil.
The first, which can be found in grasses like seashore paspalum, keeps the plant from taking in excess salt. “When you plant them in saline soil, they have the ability to exclude salt. They will not uptake saline water.” The second, which can be found in the Zoysia species she works with, enables the plants to rid themselves of the excess they absorb. “Zoysia grass does take up water, but excrete it in their salt glands on the abaxial leaf surface, so as long as you are removing the clippings, you are removing the salt.”
Selecting for salt tolerance in the field can be inconsistent, so Watkins conducts this part of the selection in the greenhouse. He grows small trays of grass in water with different salt levels, which allows him to select for tolerant genotypes. In Minnesota, salt tolerance is not only useful when it comes to water use, but also for roadsides where salt applied to ice and snow on the road washes off into the soil.
Spend Less Time Mowing
Watkins is also working on breeding grasses that do not need to be mowed as frequently, which can save homeowners, golf courses, and cities time, energy, and money. To do this, one of the things he is looking at are new species of grass such as prairie junegrass. “Prairie junegrass is native to the prairies in the western U.S., and you can also find it in Europe. It is a grass that survives really well in the harsh, arid environments in the Midwest, survives the winter, and can produce seed under harsh conditions. It grows really slowly, and it does really well without much water and when it is really hot.”
These benefits, however, come with some drawbacks that Watkins is working to change. “The problem is if you take some of these plants and mow them, they don’t make a good turf because they shred really easily, and they go dormant very quickly during drought.” Watkins thinks that the shredding is due to tough vascular tissue, which could be related to its drought hardiness, which means that it could be a tough combination to breed for. But like breeding any grass for low-input traits, the potential benefits if successful would be worth it.
“It could be pretty significant,” he says. “If you can see a 10% reduction in mowing in a city, that’s a significant impact on inputs. Fertilizers are getting more expensive—if you can cut fertilizer inputs by a third or a half, it can be significant. I think you will be able to have a full, dense lawn with its benefits without as many adverse environmental impacts.”
Green Before the Green Industry
Michael Kenna, an ASA, CSSA, and SSSA member, has been the director of Green Section Research at the United States Golf Association (USGA) for 23 years and says that the effort to reduce the environmental impact of lawns and greens is not entirely new. It has its roots in the beginnings of golf in the United States.
Due to two different individuals winning “national amateur championships,” the USGA was founded in 1894 to form a governing body to run a universally recognized national championship. But Kenna explained that around 1920, the greens at the Inverness Club in Toledo, OH were in poor shape. “They had trouble maintaining the greens, and playing conditions were not the best.”
So the USGA approached the USDA to support research into turfgrasses, which led to the creation of the Green Section at the USDA. Initially supported financially by the USGA, Kenna explains, after World War II, the Green Section was transferred to the USGA itself to continue the work.
Their Green Section research on turfgrasses has focused on many management issues, pesticides, and plant physiology, and Kenna explains that a main driving force for their research were the regional droughts across the U.S. in the late 1970s. “The focus has been to develop grasses that use less water, are more tolerant of drought, and we wanted our warm-season grasses to have improved cold tolerance.”
“We’ve been doing this a long time,” Kenna notes. “We were green long before there was a green industry. The reason why it’s come to the forefront right now is that we are in kind of an economic and environmental crossroads. We’ve had some really tough years economically across the country, and it has really affected golf. Then you have the environmental impacts with the droughts in the plains and the southern United States—these things have all made people ask for help.”
Funding for turfgrass breeding has been financially supported primarily by the turfgrass and golf industry; however, a recent change in federal grants has opened up new opportunities. The USDA Specialty Crops Research Initiative was opened to turfgrass breeding in 2008, and both Chandra and Watkins have been recipients of grants from this program.
The Back Nine of Turfgrass Breeding
Once an elite turfgrass cultivar has been developed, it will head into the National Turfgrass Evaluation Program (NTEP), where it is managed for its intended use in a five-year scientific trial conducted at many locations throughout the country, according to Kenna. “The research scientist who takes on the study will go out and rate them one to three times a month for disease problems occur, what time of year they green up, what time they go dormant in the fall, and their uniformity and density.”
Probably the most competitive position for turf is on a golf putting green. These grasses must withstand extremely close mowing and still survive after five years. They are also tested for how fast the ball rolls on the green with an inclined track called a Stimpmeter. This releases the ball at a repeatable velocity, and the distance the ball travels can be measured. Just as golfing equipment has moved from wooden clubs and balls made of crushed feathers wrapped in leather, so too, have the turfgrasses become more refined. In the 1980s, a golf ball would roll between 6 to 8 ft off of a Stimpmeter onto the putting green. Today, a competitive green will roll the ball between 9 to 10 ft.
Kenna attributes it to improvements in “managing that surface, maintaining lower cutting heights, and better genetics. All these things combine into a better surface.” This year, the USGA is helping to fund a warm-season putting green trial at NTEP, and Chandra has several elite lines that will be entered this year. “You can breed plants to do amazing things,” Kenna says. “A golf course putting green is a good example of what someone who understands population genetics can do.”
Breeding turfgrass for sustainability is not complete without good communication among breeders, seed and sod producers, and consumers. As part of his recent USDA grant, Watkins, along with his colleague at Minnesota Dr. Chengyan Yue, has done consumer preference trials to find out what people wanted in a grass. “The results were fairly similar to what we thought. They wanted grasses that they can mow less, which take in less water and result in fewer weeds. They didn’t care if it was native or not.”
Getting the message out to consumers is important to help them find what works best in their area. “Because it is so local, you have to check in with your local extension experts,” Watkins says. “That’s the first place I would go. We are considering better ways to reach the public. When it comes right down to it, a couple minutes on the local news is really effective, but it’s not always possible.”
The USGA is also working to help golfers accept changes in golf course management that reduce maintenance such as turning grass back into wild areas. “I think what the USGA is going to do over the coming years,” Kenna says, “is to highlight the best golfers in the world playing there in the U.S. Open. If you hit a bad shot, and it gets behind a pine cone, it’s a bad shot, and not because of the natural areas.”
Interested in this topic? Check out these recent publications available for purchase at www.societystore.org. Digital Library (DL) subscribers: Look for these publication in the DL at https://dl.sciencesocieties.org/.
Turfgrass: Biology, Use, and Management. Agronomy Monograph 56. A comprehensive overview of current knowledge and issues in the field of turfgrass research and management. Published by ASA, CSSA, and SSSA.
Irrigating Turfgrasses with Recycled Water. Turfgrass Slide Monograph. Attractive PowerPoint presentation summarizing the state of the science and practice today. Published by CSSA.