(Host) Barkworth & D.R. Dewey
|Distribution of Thinopyrum intermedium in North America.|
Thinopyrum intermedium, known commonly as intermediate wheatgrass, is a sod-forming perennial grass in the Triticeae tribe of Pooideae. It is part of a group of plants commonly called wheatgrasses because of the similarity of their seed heads or 'ears' to common wheat. However the wheatgrasses in general are perennial, while wheat is an annual. The grass is native to Europe and Western Asia.
Trials with intermediate wheatgrass, the product of which is trademarked by the Land Institute as "Kernza," show that it can be grown as a “multi-functional” crop, yielding various commodities as well as ecosystem services. Whereas annuals such as corn tend to deplete soil organic matter and require inputs, a perennial grain such as intermediate wheatgrass can yield crops while building soil organic matter.
Many scientific binomial names have been given to the species Thinopyrum intermedium. Multiple species or subspecies have been described based on different morphologies, like the presence or absence of pubescence. Here is a partial list of the binomial synonyms for Thinopyrum intermedium:
- Agropyron aucheri
- Agropyron ciliatiflorum
- Agropyron gentryi
- Agropyron glaucum
- Agropyron intermedium
- Agropyron podperae
- Agropyron pulcherrimum
- Agropyron trichophorum
- Elymus hispidus
- Elytrigia intermedia
Intermediate wheatgrass is the most widely used common name for Thinopyrum intermedium in the United States. The name "intermediate" probably refers to the height of the plant, which is generally somewhat shorter than Thinopyrum ponticum, known by the common name of "tall wheatgrass."
Wild triga is the common name that was given to Thinopyrum intermedium by researchers at The Rodale Institute. The name was intended to distinguish varieties of the species developed for use as a perennial grain crop from forage cultivars which are identified by the common name "intermediate wheatgrass." 
Kernza is a trademarked name held by the Land Institute for the processed grains of intermediate wheatgrass.
Origin and distribution
The native range of intermediate wheatgrass extends from central and southeastern Europe to Asia Minor. Although it was first brought to the United States in 1907, the first successful introduction to that country was from the Caucasus region in 1932. The plant can now be found growing wild throughout the Western United States and Western Canada.
- Regions with annual rainfall between 12 and 30 inches
- Soil with a pH between 5.6 and 8.4
- Locations with full exposure to sun
- A wide range of soils but with minimum depth of 16 inches
- Locations where the minimum temperature exceeds -38 °F
Thinopyrum intermedium is among the most productive forage species for the western United States. Because it heads relatively late, it can be grown effectively in mixture with alfalfa to increase its productivity, longevity, and forage quality. It regrows slowly after grazing or cutting, making it best suited to management with a single harvest per year. If multiple harvests are needed per year, other species will be more productive. If managed well, stands can persist for up to 50 years.
Habitat for wildlife - intermediate wheatgrass can be an excellent food source for grazing and browsing animals. Left unharvested, the vegetation is good nesting habitat for some birds and waterfowl. Generally, it is not an invasive plant, and coexists well with native plant species.
- Soil management
Erosion control and land rehabilitation are uses also. It establishes quickly to form a protective mat of roots and rhizomes, even when planted on soils degraded by earth moving or mining. Within five years, stands have produced up to 7000 pounds of dry root mass per acre in the top 8 inches of soil. Heavy root production holds the soil in place and restores its natural fertility by increasing the soil carbon.
Thinopyrum intermedium is a perennial grain crop. In 1983, the Rodale Research Center evaluated close to 100 species of perennial grasses to identify those with good potential for development into perennial grain crops. Intermediate wheatgrass was selected as the most promising species based on: flavor, ease of threshing, large seed size, resistance to shattering, lodging resistance, ease of harvest, and perennial growth. Intermediate wheatgrass is nutritionally similar to wheat, and the grain can be ground into flour and used for food products, including muffins, tortillas, pancakes, cookies, crackers, and breads. Some products have been marketed under the trade name Kernza.
Although the primary use of Thinopyrum intermedium is as a forage, seed production is essential because farmers and ranchers continue to establish new stands by planting seed. In 1988 over 500 metric tons of seed were harvested in Saskatchewan alone, although more recently the harvest has fallen to less than 225 metric tons in that Canadian province. Average seed yields are about 330 pounds per acre, but on-farm yields of up to 880 pounds per acre have been achieved. Seed is generally produced in rows spaced 30 to 36 inches apart. The wide row spacing (relative to grain crops like wheat) allows for sustained seed yields for five to ten years. Without spacing and occasional tillage between the rows, yields decline rapidly as the plant population becomes increasingly dense through rhizome spread. Despite this, Thinopyrum intermedium is still considered lesser than Wheat by some, as its seeds are comparatively very small.
Breeding for grain production
Intermediate wheatgrass, Thinopyrum intermedium, has been widely hybridized with wheat in the effort to transfer traits such as disease resistance or perenniality. Transferring leaf rust and powdery mildew resistance to wheat has been a special interest. But, attempts to directly domesticate the species into a grain crop did not commence until workers at the Rodale Research Center began to evaluate collections in 1983. In 1989, after assessing 300 collections, the workers selected the best twenty based on grain yield and seed quality. The selected collections were allowed to intermate, and 380 progeny were evaluated between 1991 and 1994. The best eleven plants, plus three from another evaluation, had intermated, causing a second cycle to begin. Seeds from the best plants in the second cycle were passed to scientists at The Land Institute, where the research has continued.
In 2001 and 2002, seed from the first and second breeding cycles of the Rodale Research Center was planted at The Land Institute. In the fall of 2003, 1000 individual plants were dug up and vegetatively propagated to obtain three clones of each plant. The 3000 resulting plants were randomly transplanted to the field on a three foot by three foot grid. In this manner, genetic differences between plants were separated from the environmental influences. In 2005, heads were harvested from every plant and threshed to remove the seeds. The seeds were both counted and weighed to determine the yield per seed head and weight per seed. The fifty highest plants with the highest yield and largest seed were selected to intermate in 2004.
In the fall of 2004, 4000 progeny were planted to establish the second cycle of breeding at The Land Institute. In 2008, these plants were harvested separately by using a power sythe and threshed in a combine. Again the best 50 plants were selected, this time based on yield per head, seed size, shortness, and free threshing ability.
The selection methods described above have increased seed size and yield by about 10 to 18% per cycle. But perhaps of greater importance has been the discovery of two Mendelian traits. The first is dwarfing, which results in stems about 30 cm shorter than wild type plants and short, erect leaves (see photo). The second is a more subtle change in head shape which results in thick, non-brittle heads and slightly larger seeds (see photo). Both of these traits appear to be controlled by dominant genes.
The whole aforementioned process is called mass selection, which is breeding and selecting the best individuals to spawn the next generation. Mass breeding, however, is a process by which large quantities of genetically diverse individuals are made. Due to Thinopyrum intermedium's grass-like structures, some believe that it still needs to be domesticated as much as possible to resemble wheat.
The fact that Thinopyrum intermedium is a perennial grass is important with regards to its use as a grain. The plant persists and can be harvested year after year, and its domestication would yield an additional three months of agriculture; its leaves are most active in the months in which common wheat is not active: July through September. Despite promise, the yield per acre of Thinopyrum intermedium is 26% of the yield of traditional wheat. Because of this, some are putting effort into hybridizing wheat and Thinopyrum intermedium instead of attempting to domesticate Thinopyrum intermedium to a more acceptable yield.
Hybridization with wheat
Attempts to hybridize Thinopyrum intermedium with wheat have also been done. This has some distinct advantages. First, there is wide evidence that hybridization of Thinopyrum intermedium with wheat is a method to confer fungal resistance to domestic wheat plants. However, which specific genes that protect against which specific fungus has not been as well studied. Thinopyum elongatum and Thinopyrum intermedium impart a total of four leaf rust resistance genes, while Thinopyrum intermedium confers two powdery mildew genes. There's evidence that Thinopyrum intermedium also has resistance to wheat streak mosaic virus, the Aceria tosichella mite, Barley yellow dwarf, and others. These conferred genes in wheat help increase yield and hardiness in times of environmental strain. Second, Thinopyrum intermedium also has genes that improve bread making when hybridized common wheat. While this may not seem like an important characteristic, better bread may mean more calories, feeding more people. In addition, bread that stays fresh longer may provide more opportunities for people to be adequately fed, and/or the bread can be transported to areas without much food access.
The Land Institute has been working to develop a viable wheat and Thinopyrum intermedium hybrid since 2001, and there have been several successful strains that shared 14 Thinopyrum intermedium chromosomes and 42 wheat chromosomes. These hybrids perform better in terms of yield and resistance than either of their parents, but it cannot be widespread due to the changes of climate across the world. In addition, perenniality is lost with these hybrids. This loss of perenniality is a common problem with hybridization attempts. All other desired characteristics are present in the hybrids - large seeds, good yields, etc. - except that the plants have taken on too many wheat characteristics: they are annual. However, crosses between durum wheat and Thinopyrum intermedium have resulted in hybrids that do exhibit perenniality in addition to other desired characteristics (increased vigor, hardiness in colder weather, good yield). There are two general strategies for creating an alternate grain crop. One strategy is to domesticate Thinopyrum intermedium through mass breeding and selection in order to create a strain that mimics wheat's seed size and yield but retains Thinopyum Intermedium's natural resistances, hardiness, and perenniality. In other words, this strategy gives Thinopyrum intermedium more wheat-like characteristics. A second strategy is to hybridize wheat with Thinopyrum intermedium to create a strain of wheat that mimics Thinopyrum intermedium's resistance and perenniality but retains wheat's seed size and yield. In other words, this second strategy gives wheat more Thinopyrum intermedium-like characteristics. Researchers hope that these two strategies will progress and meet in the middle.
- "Thinopyrum intermedium". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 9 December 2015.
- The Grass Manual: Thinopyrum intermedium (intermediate wheatgrass) . accessed 1.31.2013
- Intermediate Wheatgrass. Green Lands Blue Waters. Retrieved: 2013-10-26.
- Trademark information. Kernza. LegalForce. Retrieved: 2013-10-26.
- USDA PLANTS Database
- Wild Triga
- Intermediate wheatgrass fact sheet
- The Grass Manual: Distribution map for Thinopyrum intermedium (in North America; introduced species) . accessed 1/31.2013
- Intermediate Wheatgrass Plant Guide
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- Seed Production of Intermediate Wheatgrass
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- Cox 2008
- Dehaan, Lee (2014). "Current efforts to develop perennial wheat and domesticate Thinopyrum Intermedium as a perennial grain.". Genetics and Breeding: State of the Art, Gaps and Opportunities. 01: 72–89.
- Cox, Thomas (August 2006). "Prospects for Developing Perennial Grain Crops.". BioScience. 8. 56: 649–659. doi:10.1641/0006-3568(2006)56[649:PFDPGC]2.0.CO;2.
- Salina, Elena (January 25, 2015). "A Thinopyrum intermedium chromosome in bread wheat cultivars as a source of genes conferring resistance to fungal diseases.". Euphytica. 204 (1): 91–101. doi:10.1007/s10681-014-1344-5.
- Cox, Thomas (2006). "Prospects for Developing Perennial Grain Crops.". BioScience. 56 (8): 649–659. doi:10.1641/0006-3568(2006)56[649:PFDPGC]2.0.CO;2.
- Garg, Monika (2014). "Introgression of useful genes from Thinopyrum intermedium to wheat for improvement of bread-making quality.". Plant Breeding. 133 (3): 327–334. doi:10.1111/pbr.12167.
- Dehaan, Lee (2014). "Current efforts to develop perennial wheat and domesticate Thinopyrum Intermedium as a perennial grain". Genetics and Breeding: State of the Art, Gaps and Opportunities. 01: 72–89.
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