Rationale
The 2005 Synthesis Report of the United Nations’ Millennium Ecosystem Assessment program labeled agriculture the “largest threat to biodiversity and ecosystem function of any single human activity.” Perennial grains could reduce this threat, according to the following logic: *Most agricultural land is devoted to the production of grain crops: cereal, oilseed, and legume crops occupy 75% of US and 69% of global croplands. These grains include such cereal crops as wheat, rice, and maize; together they provide over 70% of human food calories. *All these grain crops are currently annual plants which are generally planted into cultivated soil. *Frequent cultivation puts soil at risk of loss and degradation. *This "central dilemma" of agriculture in which current food production undermines the potential for future food production could be escaped by developing perennial grain crops that do not require tilling the soil each year.Crop development
The current agricultural system is predominantly composed of herbaceous annuals. Annual systems depend heavily on tilling and chemical applications, like pesticides and fertilizers, and thus contribute to sustainability issues like erosion,Methods
To capitalize on the potential benefits ofPerennialization
Hybridizing existing annual crops with perennial wild relative is a common approach to perennial crop development. This approach aims to conserve the important agronomic traits that have been developed in annual grain crops while converting the plant to a perennial life cycle with well-developed long-lived root systems. However, perennialization is not without challenges. For one, plants produced through hybridization are often infertile so successful breeding of plants beyond the F1, or initial hybrid generation is rare. Second, perennial traits are often polygenic (controlled by multiple genes) so conferral of a perennial lifecycle to domesticated annual crops depends on a full suite of genes being transferred to the hybrid offspring from the perennial parent. In contrast, yield traits are generally less polygenic so single genes can have positive effects on yield. Thus, perennial crop development through hybridization may be more effective if the goal of hybridization is to introduce increased yield to perennials rather than introducing perenniality to annual crops.Accelerated domestication
Accelerated domestication (also called ''de novo'' domestication) of perennial wild plants provides another avenue for perennial crop development. This approach involves selection of wild herbaceous perennials based on their domestication potential, followed by artificial selection for agronomically important traits like yield, seed shattering (the tendency of seeds to fall off the plant or stay attached until harvest), free-threshing seeds (the tendency of seeds to easily detach from the chaff) and plant height. Pipelines for domestication, like those developed by researchers at The Land Institute, have established criteria for evaluating the potential of candidate species to be successful for domestication programs—e.g. high variability and heritability of agronomically important traits—and also guide what traits should be focused on during breeding efforts. Extensive lists of potential candidate species can be found in Wagoner & Schaeffer and Cox et al. Domesticating new perennial species has a couple of major drawbacks. For one, wild perennial grains have very low yearly yields compared to domesticated annuals so breeding efforts have to make up a lot of ground before perennial grains are commercially viable. This problem is exacerbated by the fact that many candidate species areGenetic methods
Several genetic methods can help the perennial crop development process.Advantages
Several claims have been published: #Greater access to resources through a longer season.Perennial plants typically emerge earlier than annuals in the spring and go dormant in the autumn well after annual plants have died. The longer growing season allows greater interception of sunlight and rainfall. For example, In Minnesota, annual soybean seedlings emerge from the soil in early June. By this time perennial alfalfa has grown so much that it is ready for the first harvest. Therefore, by the time a soybean crop has just begun to photosynthesize, a field of alfalfa has already produced about 40% of the season's production. #Greater access to resources through a deeper rooting zone. Most long—lived plants construct larger, deeper root systems than short-lived plants adapted to the same region . Deeper roots enable perennials to "mine" a larger volume of soil each year. A larger volume of soil also available for exploitation per unit of cropland also means a larger volume of soil water serves as a reservoir for periods without rainfall. #More efficient use of soil nutrients. Leaching of nitrogen from fertilizer has been found to be much lower under perennial crops such as alfalfa (lucerne) than annual crops such as maize. A similar phenomenon is seen in unfertilized fields harvested for wild hay. While adjacent wheat fields required annual inputs of fertilizer, the wild perennial grasses continued to produce nitrogen-rich hay for 75 to 100 years with no appreciable decline in productivity or soil fertility. Presumably, the larger root systems of the perennial plants and the microbial community they support intercept and cycle nutrients passing through the system much more efficiently than do the ephemeral root systems of crop plants. #Sustainable production on marginal lands. Cassman et al. (2003) wrote that for large areas in poor regions of the world, “annual cereal cropping …is not likely to be sustainable over the longer term because of severe erosion risk. Perennial crops and agroforestry systems are better suited to these environments.” Current perennial crops and agroforestry systems do not produce grain. Grain provides greater food security thanPotential disadvantages
# Does not address food security today. Perennial grain crops are in the early stages of development and may take many years before achieving yields equivalent to annual grains. # Makes crop rotation more difficult.Perennial grains in the marketplace
Kernza, an intermediate wheatgrass, has been under development for use as a grain crop since the 1980s. Since 2001, the nonprofit organization The Land Institute's Dr. Lee DeHaan has led development of the crop, coining the trademarked name Kernza in 2009. Recently, work on Kernza has rapidly expanded to include more than 25 lead scientists in diverse fields working on three continents. This international team has developed growing techniques and dramatically improved traits such as shatter resistance, seed size and yield, enabling the crop to now be produced and marketed at a small scale. US Institutional Kernza research partners now include the University of Minnesota, the University of Wisconsin, Madison, Cornell University, Ohio State, Kansas State, and numerous international universities in Canada and Europe, including the University of Minnesota, Lund University, and ISARA. As the first perennial grain crop grown across the northern United States, researchers hope that Kernza will help dramatically shift agriculture practice, making croplands multifunctional through the production of both food and ecosystem services. The Land Institute developed the registered trademark for Kernza grain to help identify intermediate wheatgrass grain that is certified as a perennial using the most advanced types of ''T. intermedium seed''. The cultivar of perennial rice 23 (PR23) is used for a new rice production system that is based on no-tillage.See also
* Perennial rice * Perennial sunflower *References
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