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*This "central dilemma"<ref name="Cox_etal2006" /> 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. [[No-till farming|No-till]] technology enables short-lived (annual) crops to be grown with less intense tillage, but perennial plants provide the most protection for the soil.<ref name="Ewel1986" />
*This "central dilemma"<ref name="Cox_etal2006" /> 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. [[No-till farming|No-till]] technology enables short-lived (annual) crops to be grown with less intense tillage, but perennial plants provide the most protection for the soil.<ref name="Ewel1986" />


== Perennial Grain Crop Development ==
==Methods for developing perennial grains==
The current agricultural system is predominantly composed of herbaceous [[Annual plant|annuals]]. The development of perennial grains could improve the sustainability of agriculture<ref name=":1">{{Cite journal|date=2012-10-15|title=Annual vs. perennial grain production|url=https://www.sciencedirect.com/science/article/abs/pii/S0167880912002058|journal=Agriculture, Ecosystems & Environment|language=en|volume=161|pages=1–9|doi=10.1016/j.agee.2012.05.025|issn=0167-8809}}</ref><ref name=":2">{{Cite journal|last=DeHaan|first=Lee R.|last2=Tassel|first2=David L. Van|last3=Anderson|first3=James A.|last4=Asselin|first4=Sean R.|last5=Barnes|first5=Richard|last6=Baute|first6=Gregory J.|last7=Cattani|first7=Douglas J.|last8=Culman|first8=Steve W.|last9=Dorn|first9=Kevin M.|last10=Hulke|first10=Brent S.|last11=Kantar|first11=Michael|date=2016|title=A Pipeline Strategy for Grain Crop Domestication|url=https://acsess.onlinelibrary.wiley.com/doi/abs/10.2135/cropsci2015.06.0356|journal=Crop Science|language=en|volume=56|issue=3|pages=917–930|doi=10.2135/cropsci2015.06.0356|issn=1435-0653}}</ref><ref name=":3">{{Cite journal|last=Wagoner|first=Peggy|last2=agr|first2=Jurgen R. Schaeffer Dr|date=1990-01-01|title=Perennial grain development: Past efforts and potential for the future|url=https://doi.org/10.1080/07352689009382298|journal=Critical Reviews in Plant Sciences|volume=9|issue=5|pages=381–408|doi=10.1080/07352689009382298|issn=0735-2689}}</ref><ref>{{Cite journal|last=Glover|first=J. D.|last2=Reganold|first2=J. P.|last3=Bell|first3=L. W.|last4=Borevitz|first4=J.|last5=Brummer|first5=E. C.|last6=Buckler|first6=E. S.|last7=Cox|first7=C. M.|last8=Cox|first8=T. S.|last9=Crews|first9=T. E.|last10=Culman|first10=S. W.|last11=DeHaan|first11=L. R.|date=2010-06-25|title=Increased Food and Ecosystem Security via Perennial Grains|url=https://science.sciencemag.org/content/328/5986/1638|journal=Science|language=en|volume=328|issue=5986|pages=1638–1639|doi=10.1126/science.1188761|issn=0036-8075|pmid=20576874}}</ref>. Annual systems depend heavily on tilling and chemical applications, like pesticides and fertilizers, and thus contribute to sustainability issues like erosion, [[eutrophication]] and fossil fuel use. In contrast, [[Perennial plant|perennial]] systems involve plants with deep, long lived roots, and are not dependent on tilling, could to reduce the demand for chemical applications, build [[soil health]], and sequester carbon<ref name=":3" /><ref name=":1" /> .
Thousands of years of selective breeding have produced many annual grain crops that dedicate a high proportion of their productivity to seed production; yet, no perennial grain crops have been domesticated.<ref>{{Cite journal|last=Van Tassel|first=David L.|last2=DeHaan|first2=Lee R.|last3=Cox|first3=Thomas S.|date=September 2010|title=Missing domesticated plant forms: can artificial selection fill the gap?: Missing domesticated plant forms|url=http://doi.wiley.com/10.1111/j.1752-4571.2010.00132.x|journal=Evolutionary Applications|language=en|volume=3|issue=5-6|pages=434–452|doi=10.1111/j.1752-4571.2010.00132.x|pmc=3352511|pmid=25567937}}</ref>


Annual crops have been domesticated for nearly 10,000 years, whereas no commercial perennial grains have been developed. Thus, to capitalize on the potential benefits of perennial crop domestication, the [[domestication]] process needs to be accelerated. It is unclear exactly why perennial grains were not domesticated alongside annual grains during the [[Neolithic Revolution|agricultural revolution]]<ref name=":4">{{Cite journal|last=Smaje|first=Chris|date=2015-05-28|title=The Strong Perennial Vision: A Critical Review|url=https://doi.org/10.1080/21683565.2015.1007200|journal=Agroecology and Sustainable Food Systems|volume=39|issue=5|pages=471–499|doi=10.1080/21683565.2015.1007200|issn=2168-3565}}</ref><ref name=":5">{{Cite journal|last=Tassel|first=David L. Van|last2=DeHaan|first2=Lee R.|last3=Cox|first3=Thomas S.|date=2010|title=Missing domesticated plant forms: can artificial selection fill the gap?|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1752-4571.2010.00132.x|journal=Evolutionary Applications|language=en|volume=3|issue=5-6|pages=434–452|doi=10.1111/j.1752-4571.2010.00132.x|issn=1752-4571|pmc=PMC3352511|pmid=25567937}}</ref>. Annuals may have been predisposed to domestication for several reasons. For one, wild annuals were likely easier targets for early domestication efforts because they generally have greater yields than wild perennials. The [[Fitness (biology)|fitness]] of annual plants depends on the reproductive output of a single year so plants naturally invest heavily in seed production (the product of interest for agriculture). In contrast, perennials have to balance seed production with overwinter survival and thus produce lower yields<ref name=":5" />. Second, annual plants have a shorter generation time, facilitating faster gains through the [[Selective breeding|artificial selection]] process<ref name=":5" />. Third, early agriculture utilized plowing to clear fields for the following year’s crop and the practice of annual tilling is not compatible with perennial grains<ref name=":5" />. Finally, once annual grains were domesticated there was no longer a reduced incentive to pursue the domestication of new perennial grains<ref name=":5" />.
Three ways of developing perennial grain crops have been proposed:<ref name="GloverReganold_etal2010" /><ref name="Cox_etal2006" /><ref name="Cox_etal2002" />

# The primary [[gene pool]]s of several domesticated grain crops include perennial types, even though these crops are generally grown as annuals. [[Pigeon pea]] is a large-seeded grain legume ([[pulse]]) with both short-season (annual) and long-season (perennial) varieties.<ref name= "Snapp_etal2003" /> If the highest-yielding annual varieties were hybridized with the longest-living varieties, robustly perennial, high-yielding varieties could be developed.
If the limitations of early domestication efforts explain the lack of perennial grains, there may not be an insurmountable physiological barrier to high yielding perennials. For instance, the trade off between survival and yield in perennials should primarily be observed in the plant's first year when they are establishing root structures. In subsequent years, perennials may actually benefit from having a longer growing season and greater access to soil resources due to pre-established root systems ( which can also reduce reliance on fertilizer)<ref name=":6">{{Cite journal|last=DeHaan|first=L. R.|last2=Tassel|first2=D. L. Van|last3=Cox|first3=T. S.|date=2005/03|title=Perennial grain crops: A synthesis of ecology and plant breeding|url=https://www.cambridge.org/core/journals/renewable-agriculture-and-food-systems/article/abs/perennial-grain-crops-a-synthesis-of-ecology-and-plant-breeding/72023203E46F43C90C3C857B68BD2948|journal=Renewable Agriculture and Food Systems|language=en|volume=20|issue=1|pages=5–14|doi=10.1079/RAF200496|issn=1742-1713}}</ref>. However, even if physiological limitations limit resource allocation to seed production in perennials, their yields may still be comparable to or exceed annual grain yields due to improved resource acquisition and higher overall [[Biomass (ecology)|biomass]]<ref name=":5" />.
# The secondary or tertiary gene pools of most domesticated grain crops include perennial species.<ref name= "Cox_etal2002" /> Gene exchange between such species is possible, though sometimes difficult. Genes enhancing the agronomic traits of wild perennials, increased seed size, for example, could be brought in from domestic grain relatives. Alternately, genes increasing the lifespan of domesticated grains could be obtained by crossing with wild perennial relatives. For example, domestic Asian rice can be crossed with wild perennial rice species to exchange genes for many traits.

# Wild perennial plants with oil-, carbohydrate- or protein-rich seeds could be [[Domestication|domesticated]] without any wide hybridization. Although our grain crops were all domesticated thousands of years ago, modern genetic theory and molecular genetic techniques may greatly accelerate the process compared with the original process of domestication.<ref name= "NAS" /> [http://www.rodaleinstitute.org The Rodale Institute] and [http://www.landinstitute.org The Land Institute] have each had plant breeding projects in which a wild, perennial grass, ''[[Thinopyrum intermedium]]'' was subjected to recurrent cycles of selection for improved grain traits.<ref name= "Wagoner1990" /><ref name= "Cox_etal2006" /> The land Institute since has begun marketing their work under the trade name [[Kernza]]®.
While perennial crop domestication could alleviate some of the sustainability issues caused by reliance on annual crops, the gains may still be fundamentally limited by general agricultural practices. Producing grain on scales large enough to meet the world demand depends on the conversion of massive tracts of native grassland to agriculture, regardless of the perennial or annual nature of the crop<ref name=":4" />.

=== Crop Development Methods ===
           Serious efforts to develop new perennial grains began in the 1980s, largely driven by [[Wes Jackson]] and [[The Land Institute]] in Salina, Kansas<ref>{{Cite journal|last=Crain|first=Jared|last2=Bajgain|first2=Prabin|last3=Anderson|first3=James|last4=Zhang|first4=Xiaofei|last5=DeHaan|first5=Lee|last6=Poland|first6=Jesse|date=2020|title=Enhancing Crop Domestication Through Genomic Selection, a Case Study of Intermediate Wheatgrass|url=https://www.frontiersin.org/articles/10.3389/fpls.2020.00319/full|journal=Frontiers in Plant Science|language=English|volume=11|doi=10.3389/fpls.2020.00319|issn=1664-462X|pmc=PMC7105684|pmid=32265968}}</ref>. Approaches to perennial crop development generally fall under three main methods: perennialization, de novo domestication, and genetic manipulation. These methods are not mutually exclusive and can be used in tandem.

==== Perennialization ====
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<ref name=":7">{{Cite journal|last=Cox|first=T. S.|last2=Bender|first2=M.|last3=Picone|first3=C.|last4=Tassel|first4=D. L. Van|last5=Holland|first5=J. B.|last6=Brummer|first6=E. C.|last7=Zoeller|first7=B. E.|last8=Paterson|first8=A. H.|last9=Jackson|first9=W.|date=2002-03-01|title=Breeding Perennial Grain Crops|url=https://www.tandfonline.com/doi/abs/10.1080/0735-260291044188|journal=Critical Reviews in Plant Sciences|volume=21|issue=2|pages=59–91|doi=10.1080/0735-260291044188|issn=0735-2689}}</ref>. However, it is not without challenges.

For one, plants produced through [[Hybrid (biology)|hybridization]] are often infertile so successful breeding of plants beyond the [[F1 hybrid|F1]], or initial hybrid generation is rare<ref>{{Cite journal|last=Cox|first=T. S.|last2=Tassel|first2=D. L. Van|last3=Cox|first3=C. M.|last4=DeHaan|first4=L. R.|date=2010-07-27|title=Progress in breeding perennial grains|url=https://www.publish.csiro.au/cp/CP09201|journal=Crop and Pasture Science|language=en|volume=61|issue=7|pages=513–521|doi=10.1071/CP09201|issn=1836-5795}}</ref>. 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. Yield traits are generally less polygenic so single genes can have positive effects on yield. 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<ref name=":7" /> .

==== De Novo Domestication ====
De novo domestication of perennial wild plants provides another avenue for perennial crop development. This approach involves selection of wild perennial grasses 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<ref name=":2" />. Existing pipelines  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<ref>{{Cite journal|last=DeHaan|first=Lee|last2=Larson|first2=Steve|last3=López-Marqués|first3=Rosa L.|last4=Wenkel|first4=Stephan|last5=Gao|first5=Caixia|last6=Palmgren|first6=Michael|date=2020-06|title=Roadmap for Accelerated Domestication of an Emerging Perennial Grain Crop|url=https://doi.org/10.1016/j.tplants.2020.02.004|journal=Trends in Plant Science|volume=25|issue=6|pages=525–537|doi=10.1016/j.tplants.2020.02.004|issn=1360-1385}}</ref><ref>{{Cite journal|last=Schlautman|first=Brandon|last2=Barriball|first2=Spencer|last3=Ciotir|first3=Claudia|last4=Herron|first4=Sterling|last5=Miller|first5=Allison J.|date=2018/3|title=Perennial Grain Legume Domestication Phase I: Criteria for Candidate Species Selection|url=https://www.mdpi.com/2071-1050/10/3/730|journal=Sustainability|language=en|volume=10|issue=3|pages=730|doi=10.3390/su10030730}}</ref>. Extensive lists of potential candidate species can be found in Wagoner & Schaeffer<ref name=":3" />  and Cox et al.<ref>{{Cite journal|last=Cox|first=T. S.|last2=Bender|first2=M.|last3=Picone|first3=C.|last4=Tassel|first4=D. L. Van|last5=Holland|first5=J. B.|last6=Brummer|first6=E. C.|last7=Zoeller|first7=B. E.|last8=Paterson|first8=A. H.|last9=Jackson|first9=W.|date=2002-03-01|title=Breeding Perennial Grain Crops|url=https://www.tandfonline.com/doi/abs/10.1080/0735-260291044188|journal=Critical Reviews in Plant Sciences|volume=21|issue=2|pages=59–91|doi=10.1080/0735-260291044188|issn=0735-2689}}</ref>.

Domesticating new perennial species has a couple of major drawbacks. For one, wild perennial grains have very low yields compared to domesticated annuals so breeding efforts have a lot of ground to make up before perennial grains are commercially viable. This problem is exacerbated by the fact that many candidate species are [[Polyploidy|polyploid]] (i.e. they have extra sets of genetic material). Polyploidy makes it harder to breed undesirable alleles out of the population and create uniform plants that grow and mature simultaneously for easy harvest<ref name=":6" />.

==== Genetic Methods ====
Several genetic methods can help the perennial crop development process. [[Molecular breeding|Genomic selection]], a method of predicting plant traits based on analysis of their genome, shows promise as a method to accelerate selection of plants in domestication programs. If adult plant [[Phenotype|phenotypes]] can be predicted from the [[Genome|genomes]] of young plants, plants can be artificially selected at an earlier age, reducing time and resources needed to identify individuals with desirable traits<ref>{{Cite journal|last=Crain|first=Jared|last2=Bajgain|first2=Prabin|last3=Anderson|first3=James|last4=Zhang|first4=Xiaofei|last5=DeHaan|first5=Lee|last6=Poland|first6=Jesse|date=2020|title=Enhancing Crop Domestication Through Genomic Selection, a Case Study of Intermediate Wheatgrass|url=https://www.frontiersin.org/articles/10.3389/fpls.2020.00319/full|journal=Frontiers in Plant Science|language=English|volume=11|doi=10.3389/fpls.2020.00319|issn=1664-462X|pmc=PMC7105684|pmid=32265968}}</ref>. [[Genetically modified organism|Transgenics]] and gene altering can add or target “domestication genes” and their [[Sequence homology|orthologs]] (genes with similar sequences and functions) in perennial plants. Domestication genes have known effects on traits that are relevant to domestication, and have been discovered in annual crop species. Genome sequencing indicates that many orthologs also exist in perennial species that may be useful targets for genetic alteration<ref name=":8">{{Cite journal|last=DeHaan|first=Lee|last2=Larson|first2=Steve|last3=López-Marqués|first3=Rosa L.|last4=Wenkel|first4=Stephan|last5=Gao|first5=Caixia|last6=Palmgren|first6=Michael|date=2020-06|title=Roadmap for Accelerated Domestication of an Emerging Perennial Grain Crop|url=https://doi.org/10.1016/j.tplants.2020.02.004|journal=Trends in Plant Science|volume=25|issue=6|pages=525–537|doi=10.1016/j.tplants.2020.02.004|issn=1360-1385}}</ref>.

           Current applications of genetic manipulation are limited because the genomes of many candidate species have not been sequenced. Furthermore, methods of genetic manipulation have not yet been optimized in most candidate species<ref name=":7" /><ref name=":8" />. Despite these limitations, there have been rapid gains the development of genetic techniques and these methods are likely to be a useful aid for the development of perennial crops in years to come<ref name=":8" />.


==Advantages of perennial crops==
==Advantages of perennial crops==

Revision as of 05:19, 17 April 2021

Roots of intermediate wheatgrass, a perennial grain candidate compared to those of annual wheat (at left in each panel)

A perennial grain is a grain crop that lives and remains productive for two or more years, rather than growing for only one season before harvest, like most grains and annual crops. While many fruit, nut and forage crops are long-lived perennial plants, all major grain crops presently used in large-scale agriculture are annuals or short-lived perennials grown as annuals. Scientists from several nations have argued that perennial versions of today's grain crops could be developed and that these perennial grains could make grain agriculture more sustainable.[1][2][3][4]

Rationale

Cultivation often has a negative impact on provision of [ecosystem] services. For example, cultivated systems tend to use more water, increase water pollution and soil erosion, store less carbon, emit more greenhouse gases, and support significantly less habitat and biodiversity than the ecosystems they replace

The Millennium Ecosystem Assessment[4]

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.”[4] 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.[5]
  • 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.[4]
  • This "central dilemma"[6] 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. No-till technology enables short-lived (annual) crops to be grown with less intense tillage, but perennial plants provide the most protection for the soil.[7]

Perennial Grain Crop Development

The current agricultural system is predominantly composed of herbaceous annuals. The development of perennial grains could improve the sustainability of agriculture[8][9][10][11]. Annual systems depend heavily on tilling and chemical applications, like pesticides and fertilizers, and thus contribute to sustainability issues like erosion, eutrophication and fossil fuel use. In contrast, perennial systems involve plants with deep, long lived roots, and are not dependent on tilling, could to reduce the demand for chemical applications, build soil health, and sequester carbon[10][8] .

Annual crops have been domesticated for nearly 10,000 years, whereas no commercial perennial grains have been developed. Thus, to capitalize on the potential benefits of perennial crop domestication, the domestication process needs to be accelerated. It is unclear exactly why perennial grains were not domesticated alongside annual grains during the agricultural revolution[12][13]. Annuals may have been predisposed to domestication for several reasons. For one, wild annuals were likely easier targets for early domestication efforts because they generally have greater yields than wild perennials. The fitness of annual plants depends on the reproductive output of a single year so plants naturally invest heavily in seed production (the product of interest for agriculture). In contrast, perennials have to balance seed production with overwinter survival and thus produce lower yields[13]. Second, annual plants have a shorter generation time, facilitating faster gains through the artificial selection process[13]. Third, early agriculture utilized plowing to clear fields for the following year’s crop and the practice of annual tilling is not compatible with perennial grains[13]. Finally, once annual grains were domesticated there was no longer a reduced incentive to pursue the domestication of new perennial grains[13].

If the limitations of early domestication efforts explain the lack of perennial grains, there may not be an insurmountable physiological barrier to high yielding perennials. For instance, the trade off between survival and yield in perennials should primarily be observed in the plant's first year when they are establishing root structures. In subsequent years, perennials may actually benefit from having a longer growing season and greater access to soil resources due to pre-established root systems ( which can also reduce reliance on fertilizer)[14]. However, even if physiological limitations limit resource allocation to seed production in perennials, their yields may still be comparable to or exceed annual grain yields due to improved resource acquisition and higher overall biomass[13].

While perennial crop domestication could alleviate some of the sustainability issues caused by reliance on annual crops, the gains may still be fundamentally limited by general agricultural practices. Producing grain on scales large enough to meet the world demand depends on the conversion of massive tracts of native grassland to agriculture, regardless of the perennial or annual nature of the crop[12].

Crop Development Methods

           Serious efforts to develop new perennial grains began in the 1980s, largely driven by Wes Jackson and The Land Institute in Salina, Kansas[15]. Approaches to perennial crop development generally fall under three main methods: perennialization, de novo domestication, and genetic manipulation. These methods are not mutually exclusive and can be used in tandem.

Perennialization

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[16]. However, it 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[17]. 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. Yield traits are generally less polygenic so single genes can have positive effects on yield. 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[16] .

De Novo Domestication

De novo domestication of perennial wild plants provides another avenue for perennial crop development. This approach involves selection of wild perennial grasses 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[9]. Existing pipelines  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[18][19]. Extensive lists of potential candidate species can be found in Wagoner & Schaeffer[10]  and Cox et al.[20].

Domesticating new perennial species has a couple of major drawbacks. For one, wild perennial grains have very low yields compared to domesticated annuals so breeding efforts have a lot of ground to make up before perennial grains are commercially viable. This problem is exacerbated by the fact that many candidate species are polyploid (i.e. they have extra sets of genetic material). Polyploidy makes it harder to breed undesirable alleles out of the population and create uniform plants that grow and mature simultaneously for easy harvest[14].

Genetic Methods

Several genetic methods can help the perennial crop development process. Genomic selection, a method of predicting plant traits based on analysis of their genome, shows promise as a method to accelerate selection of plants in domestication programs. If adult plant phenotypes can be predicted from the genomes of young plants, plants can be artificially selected at an earlier age, reducing time and resources needed to identify individuals with desirable traits[21]. Transgenics and gene altering can add or target “domestication genes” and their orthologs (genes with similar sequences and functions) in perennial plants. Domestication genes have known effects on traits that are relevant to domestication, and have been discovered in annual crop species. Genome sequencing indicates that many orthologs also exist in perennial species that may be useful targets for genetic alteration[22].

           Current applications of genetic manipulation are limited because the genomes of many candidate species have not been sequenced. Furthermore, methods of genetic manipulation have not yet been optimized in most candidate species[16][22]. Despite these limitations, there have been rapid gains the development of genetic techniques and these methods are likely to be a useful aid for the development of perennial crops in years to come[22].

Advantages of perennial crops

Several claims have been published:[6]

  1. 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.[23]
  2. 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.[3] 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.
  3. 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.[24][25] A similar phenomenon is seen in unfertilized fields harvested for wild hay.[26] 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.
  4. 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.”[27] Current perennial crops and agroforestry systems do not produce grain. Grain provides greater food security than forage or fruit because it can be eaten directly by humans (unlike forage) and it can be stored (unlike fruit) for consumption during the winter or dry season.
  5. Reduced Soil erosion U.S. Forest Service et al. cite perennial grasses as a preventative for soil erosion.[28] Perennials of all kinds establish thick root systems which tie up soil and prevent surface erosion by wind and water. Since water runoff is slowed, it has a longer time to soak in and enter the groundwater system. Net water inflow into streams is marginally reduced due to groundwater infusion, but this also reduces high flow rates in streams associated with fast-flowing water-based erosion of streambeds. .
  6. Increased wildlife populations U.S. Forest Service et all cite slower release of water into streams, which makes water levels more consistent instead of alternating between dry and flash-flood situations common to deserts. Consistent water levels contribute to increased wildlife populations of fish, amphibians, waterfowl, and mammals dependent upon a consistent water source.[28]
  7. Reduced weed competition" - Minimizing tillage and herbicide applications.
  8. Improved soil microbiomes - Perennial grain crops may nurture beneficial soil microbiomes, as the frequent soil disturbance required in annual crop production is disruptive to these microbiomes.
  9. Sequester more carbon - It is perenial grains may sequester more carbon, due to better landscape management, and maintaining more cropland in production.[29][25]

Potential disadvantages of perennial crops

  1. 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.
  2. Makes crop rotation more difficult. Crop rotations with perennial systems are possible, but the full rotation will necessarily take longer. For example, a perennial hay crop[30] like alfalfa is commonly rotated with annual crops or other perennial hay crops after 3–5 years. The slower pace of rotation—compared with annual crops—could allow a greater buildup of pathogens, pests or weeds in the perennial phase of the rotation.
  3. Builds soil organic matter at the expense of plant productivity. In the absence of tillage, and in soils with depleted organic matter, crops with large root systems may build up organic matter to the point that nearly all of the soil nitrogen and phosphorus is immobilized. When this happens, productivity may decline until either the organic matter builds up to a level where equilibrium is reached between nutrient mineralization and nutrient immobilization or fertilizer is added to the system.
  4. Hydrological impacts. Perennial plants may intercept and utilize more of the incoming rainfall.[3] than annual plants each year. This may result in water tables dropping and/or reduced surface flow to rivers.
  5. Reduced nutrient delivery to downstream farms. Wide replacement of annual with perennial plants on agricultural landscapes could stabilize soils and reduce nitrate leaching to the point that the delivery of sediment and dissolved nitrogen to downstream landscapes could be reduced. Farmers in these areas may currently rely on these nutrient inputs. On the other hand, other sectors might benefit from improved water quality.
  6. Improved habitat for pests. If fields are not left bare for a portion of the year, rodents and insects populations may increase. Burning of the stubble of perennial grains could reduce these populations, but burning may not be permitted in some areas. Furthermore, rodents and insects living underground would survive burning, whereas tillage disrupts their habitat.

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.[7]

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.[31]

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.[1]

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.

Patagonia Provisions was the first company to develop a commercial retail product made from Kernza® perennial grain for the mainstream marketplace. Patagonia took a significant risk, breaking through the initial barrier to new product development and market entry with Long Root Ale.

The initiative and investment on the part of Patagonia Provisions to bring Long Root Ale to market helped pave the way for other partnerships and potential Kernza® products becoming more widely available to consumers.

Currently, there are a number of restaurants serving products made with Kernza®, including Birchwood Cafe in Minneapolis, The Perennial in San Francisco, Cafe Gratitude in the Los Angeles metro, and Avalanche Pizza in Athens, OH.

Hopworks Urban Brewery in Portland, OR and Vancouver, WA brewed Long Root Ale for Patagonia Provisions and has it on tap, in addition to the ale in four-pack cans being sold in Whole Foods in California. Bang! Brewing in St. Paul, MN has a Kernza® beer available, as does Blue Skye Brewery near us in Salina, KS.

Innovative Dumpling & Strand produces Kernza® pasta that they retail through Twin Cities-area farmers’ markets.

Additionally, Cascadian Farm plans to incorporate Kernza® into some of its foods, with expectations for products made with Kernza® available in retail markets by late 2019. Cascadian Farm’s commitment to purchase has spurred researchers and farmers to plant on commercial-scale fields versus the test sized plots currently being grown.[31]

See also

References

  1. ^ a b Wagoner, P.; Schaeffer, J. R. (1990). "Perennial grain development: Past efforts and potential for the future". Critical Reviews in Plant Sciences. 9 (5): 381. doi:10.1080/07352689009382298.
  2. ^ National Research Council of the National Academies. 2010. Toward Sustainable Agricultural Systems in the 21st Century. National Academy Press, Washington D.C. pp 249-251.
  3. ^ a b c Glover, J. D.; Reganold, J. P.; Bell, L. W.; Borevitz, J.; Brummer, E. C.; Buckler, E. S.; Cox, C. M.; Cox, T. S.; Crews, T. E.; Culman, S. W.; Dehaan, L. R.; Eriksson, D.; Gill, B. S.; Holland, J.; Hu, F.; Hulke, B. S.; Ibrahim, A. M. H.; Jackson, W.; Jones, S. S.; Murray, S. C.; Paterson, A. H.; Ploschuk, E.; Sacks, E. J.; Snapp, S.; Tao, D.; Van Tassel, D. L.; Wade, L. J.; Wyse, D. L.; Xu, Y. (2010). "Increased Food and Ecosystem Security via Perennial Grains". Science. 328 (5986): 1638–1639. doi:10.1126/science.1188761. PMID 20576874.
  4. ^ a b c d Cassman KG, Wood S. 2005. "Cultivated systems". Chapter 26 in Millennium Ecosystem Assessment, Ecosystems and Human Well-Being: Current State and Trends. Washington (DC): Island Press. Chiras DD, Reganold JP, Owen OS. 2004 Natural Resource Conservation. Upper Saddle River, New Jersey: Prentice-Hall.
  5. ^ Glover, JD, Reganold, JP. 2010. Perennial grains: Food security for the future. Issues in Science and Technology. Winter 2010:41-47.
  6. ^ a b Cox, T. S.; Glover, J. D.; Van Tassel, D. L.; Cox, C. M.; Dehaan, L. E. R. (2006). "Prospects for Developing Perennial Grain Crops". BioScience. 56 (8): 649. doi:10.1641/0006-3568(2006)56[649:PFDPGC]2.0.CO;2.
  7. ^ a b Ewel, J. J. (1986). "Designing Agricultural Ecosystems for the Humid Tropics". Annual Review of Ecology and Systematics. 17: 245–271. doi:10.1146/annurev.es.17.110186.001333.
  8. ^ a b "Annual vs. perennial grain production". Agriculture, Ecosystems & Environment. 161: 1–9. 2012-10-15. doi:10.1016/j.agee.2012.05.025. ISSN 0167-8809.
  9. ^ a b DeHaan, Lee R.; Tassel, David L. Van; Anderson, James A.; Asselin, Sean R.; Barnes, Richard; Baute, Gregory J.; Cattani, Douglas J.; Culman, Steve W.; Dorn, Kevin M.; Hulke, Brent S.; Kantar, Michael (2016). "A Pipeline Strategy for Grain Crop Domestication". Crop Science. 56 (3): 917–930. doi:10.2135/cropsci2015.06.0356. ISSN 1435-0653.
  10. ^ a b c Wagoner, Peggy; agr, Jurgen R. Schaeffer Dr (1990-01-01). "Perennial grain development: Past efforts and potential for the future". Critical Reviews in Plant Sciences. 9 (5): 381–408. doi:10.1080/07352689009382298. ISSN 0735-2689.
  11. ^ Glover, J. D.; Reganold, J. P.; Bell, L. W.; Borevitz, J.; Brummer, E. C.; Buckler, E. S.; Cox, C. M.; Cox, T. S.; Crews, T. E.; Culman, S. W.; DeHaan, L. R. (2010-06-25). "Increased Food and Ecosystem Security via Perennial Grains". Science. 328 (5986): 1638–1639. doi:10.1126/science.1188761. ISSN 0036-8075. PMID 20576874.
  12. ^ a b Smaje, Chris (2015-05-28). "The Strong Perennial Vision: A Critical Review". Agroecology and Sustainable Food Systems. 39 (5): 471–499. doi:10.1080/21683565.2015.1007200. ISSN 2168-3565.
  13. ^ a b c d e f Tassel, David L. Van; DeHaan, Lee R.; Cox, Thomas S. (2010). "Missing domesticated plant forms: can artificial selection fill the gap?". Evolutionary Applications. 3 (5–6): 434–452. doi:10.1111/j.1752-4571.2010.00132.x. ISSN 1752-4571. PMC 3352511. PMID 25567937.{{cite journal}}: CS1 maint: PMC format (link)
  14. ^ a b DeHaan, L. R.; Tassel, D. L. Van; Cox, T. S. (2005/03). "Perennial grain crops: A synthesis of ecology and plant breeding". Renewable Agriculture and Food Systems. 20 (1): 5–14. doi:10.1079/RAF200496. ISSN 1742-1713. {{cite journal}}: Check date values in: |date= (help)
  15. ^ Crain, Jared; Bajgain, Prabin; Anderson, James; Zhang, Xiaofei; DeHaan, Lee; Poland, Jesse (2020). "Enhancing Crop Domestication Through Genomic Selection, a Case Study of Intermediate Wheatgrass". Frontiers in Plant Science. 11. doi:10.3389/fpls.2020.00319. ISSN 1664-462X. PMC 7105684. PMID 32265968.{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link)
  16. ^ a b c Cox, T. S.; Bender, M.; Picone, C.; Tassel, D. L. Van; Holland, J. B.; Brummer, E. C.; Zoeller, B. E.; Paterson, A. H.; Jackson, W. (2002-03-01). "Breeding Perennial Grain Crops". Critical Reviews in Plant Sciences. 21 (2): 59–91. doi:10.1080/0735-260291044188. ISSN 0735-2689.
  17. ^ Cox, T. S.; Tassel, D. L. Van; Cox, C. M.; DeHaan, L. R. (2010-07-27). "Progress in breeding perennial grains". Crop and Pasture Science. 61 (7): 513–521. doi:10.1071/CP09201. ISSN 1836-5795.
  18. ^ DeHaan, Lee; Larson, Steve; López-Marqués, Rosa L.; Wenkel, Stephan; Gao, Caixia; Palmgren, Michael (2020-06). "Roadmap for Accelerated Domestication of an Emerging Perennial Grain Crop". Trends in Plant Science. 25 (6): 525–537. doi:10.1016/j.tplants.2020.02.004. ISSN 1360-1385. {{cite journal}}: Check date values in: |date= (help)
  19. ^ Schlautman, Brandon; Barriball, Spencer; Ciotir, Claudia; Herron, Sterling; Miller, Allison J. (2018/3). "Perennial Grain Legume Domestication Phase I: Criteria for Candidate Species Selection". Sustainability. 10 (3): 730. doi:10.3390/su10030730. {{cite journal}}: Check date values in: |date= (help)CS1 maint: unflagged free DOI (link)
  20. ^ Cox, T. S.; Bender, M.; Picone, C.; Tassel, D. L. Van; Holland, J. B.; Brummer, E. C.; Zoeller, B. E.; Paterson, A. H.; Jackson, W. (2002-03-01). "Breeding Perennial Grain Crops". Critical Reviews in Plant Sciences. 21 (2): 59–91. doi:10.1080/0735-260291044188. ISSN 0735-2689.
  21. ^ Crain, Jared; Bajgain, Prabin; Anderson, James; Zhang, Xiaofei; DeHaan, Lee; Poland, Jesse (2020). "Enhancing Crop Domestication Through Genomic Selection, a Case Study of Intermediate Wheatgrass". Frontiers in Plant Science. 11. doi:10.3389/fpls.2020.00319. ISSN 1664-462X. PMC 7105684. PMID 32265968.{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link)
  22. ^ a b c DeHaan, Lee; Larson, Steve; López-Marqués, Rosa L.; Wenkel, Stephan; Gao, Caixia; Palmgren, Michael (2020-06). "Roadmap for Accelerated Domestication of an Emerging Perennial Grain Crop". Trends in Plant Science. 25 (6): 525–537. doi:10.1016/j.tplants.2020.02.004. ISSN 1360-1385. {{cite journal}}: Check date values in: |date= (help)
  23. ^ CC Sheaffer, Martin NP, Lamb JAFS, Cuomo GR, Jewett JG, Quering SR. 2000. Leaf and stem properties of alfalfa entries. Agronomy Journal 92:733-739.
  24. ^ Huggins, D. R.; Randall, G. W.; Russelle, M. P. (2001). "Subsurface Drain Losses of Water and Nitrate following Conversion of Perennials to Row Crops". Agronomy Journal. 93 (3): 477. doi:10.2134/agronj2001.933477x.
  25. ^ a b Culman, Steve W., Sieglinde S. Snapp, Mary Ollenburger, Bruno Basso, and Lee R. DeHaan. “Soil and water quality rapidly responds to the perennial grain Kernza wheatgrass.” Agronomy Journal 105, no. 3 (2013): 735-744.
  26. ^ [1][permanent dead link] JD Glover, SW Culman, ST DuPont, W Broussard, L Young, ME Mangan,JG Mai, TE Crews, LR DeHaan, DH Buckley, H Ferris, RE Turner, HL Reynolds and DL Wyse. 2010. Harvested perennial grasslands provide ecological benchmarks for agricultural sustainabilityAgriculture, Ecosystems & Environment. 137:3-12.
  27. ^ KG Cassman, A Dobermann, DT Walters, H Yang. 2003. Meeting cereal demand while protecting natural resources and improving environmental quality. Annual Review of Environment and Resources 28:315-358.
  28. ^ a b United States Forest Service, division of United States Department of Agriculture, "FSH 2509.22 – SOIL AND WATER CONSERVATION HANDBOOK, CHAPTER 10 – WATER QUALITY MANAGEMENT FOR NATIONAL FOREST SYSTEM LANDS IN ALASKA
  29. ^ Paustian, Keith, Johannes Lehmann, Stephen Ogle, David Reay, G. Philip Robertson, and Pete Smith. “Climate-smart soils.” Nature 532, no. 7597 (2016): 49-57.
  30. ^ Markle, G. M.; Baron, J. J.; Schneider, B.A. 1998. Food and Feed Crops of the United States, Second Edition; Meister Publishing Co.: Willoughby, OH.
  31. ^ a b "Kernza® Grain & Perennial Agriculture | The Land Institute". The Land Institute. Retrieved 2017-12-14.

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