(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.
- Thinopyrum intermedium is best adapted to:
- 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.
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.
Breeding for Grain Production
Intermediate wheatgrass, Thinopyrum intermedium, has been widely hybridized with wheat in efforts to transfer traits like disease resistance or perenniality to wheat. But attempts to directly domesticate the species as a grain crop did not begin until workers at the Rodale Research Center began to evaluate collections in 1983. After evaluating 300 collections, the best 20 based on grain yield and seed quality were selected in 1989. The selected collections were allowed to intermate, and 380 progeny were evaluated between 1991 and 1994. The best 11 plants, plus three from another evaluation, were interemated, and a second cycle was begun. 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 individuals 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 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
- Wagoner, P., and A. Schauer. 1990. Intermediate wheatgrass as a perennial grain crop. p. 143-145. In: J. Janick and J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.
- Seed Production of Intermediate Wheatgrass
- Cox et al. 2002 Breeding Perennial Grain Crops. Critical Reviews in Plant Science 21:51-91
- A. Schauer, 1990. Evaluation of Intermediate Wheatgrass Germplasm. Rodale Research Center, Kutztown, Pennsylvania.
- Cox 2008
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