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In the interest of diversifying the global food system, improving human nutrition, and making agriculture more sustainable, there have been many proposals to domesticate wild plants or complete the domestication of semi-domesticated “orphan” crops. However, very few new crops have recently been fully domesticated. Many wild plants have traits limiting their production or consumption that could be costly and slow to change. Others may have fortuitous pre-adaptations that make them easier to develop or feasible as high-value, albeit low-yielding, crops. To increase success in contemporary domestication of new crops, we propose a “pipeline” approach, with attrition expected as species advance through the pipeline. We list criteria for ranking domestication candidates to help enrich the starting pool with more pre-adapted, promising species. We also discuss strategies for prioritizing initial research efforts once the candidates have been selected: developing higher value products and services from the crop, increasing yield potential, and focusing on overcoming undesirable traits. Finally, we present new-crop case studies which demonstrate that wild species' limitations and potential (in agronomic culture, shattering, seed size, harvest, cleaning, hybridization, etc.) are often only revealed during the early phases of domestication. When nearly insurmountable barriers were reached in some species, they have been (at least temporarily) eliminated from the pipeline. Conversely, a few species have moved quickly through the pipeline as hurdles such as low seed weight or low seed number per head were rapidly overcome, leading to increased confidence, farmer collaboration, and program expansion.
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crop science, vol. 56, m ayjune 2016 www.crops.org 1
opinion & policy
N  could provide a wide array of benets to farmers,
consumers, and the environment (Bates, 1985; Janick et al.,
1996). New grains with novel life histories (perennial or winter
annual) could have particularly high potential impact given the
large economic and environmental footprint of current grain crops
A Pipeline Strategy
for Grain Crop Domestication
Lee R. DeHaan,* David L. Van Tassel, James A. Anderson, Sean R. Asselin, Richard Barnes,
Gregory J. Baute, Douglas J. Cattani, Steve W. Culman, Kevin M. Dorn, Brent S. Hulke,
Michael Kantar, Steve Larson, M. David Marks, Allison J. Miller, Jesse Poland, Damian A. Ravetta,
Emily Rude, Matthew R. Ryan, Don Wyse, and Xiaofei Zhang
ABSTRACT
In the interest of diversifying the global food
system, improving human nutrition, and making
agriculture more sustainable, there have been
many proposals to domesticate wild plants or
complete the domestication of semidomesti-
cated orphan crops. However, very few new
crops have recently been fully domesticated.
Many wild plants have traits limiting their pro-
duction or consumption that could be costly
and slow to change. Others may have fortu-
itous preadaptations that make them easier to
develop or feasible as high-value, albeit low-
yielding, crops. To increase success in contem-
porary domestication of new crops, we propose
a pipeline approach, with attrition expected as
species advance through the pipeline. We list
criteria for ranking domestication candidates
to help enrich the starting pool with more pre-
adapted, promising species. We also discuss
strategies for prioritizing initial research efforts
once the candidates have been selected: devel-
oping higher value products and services from
the crop, increasing yield potential, and focus-
ing on overcoming undesirable traits. Finally,
we present new-crop case studies that demon-
strate that wild species’ limitations and poten-
tial (in agronomic culture, shattering, seed size,
harvest, cleaning, hybridization, etc.) are often
only revealed during the early phases of domes-
tication. When nearly insurmountable barriers
were reached in some species, they have been
(at least temporarily) eliminated from the pipe-
line. Conversely, a few species have moved
quickly through the pipeline as hurdles, such as
low seed weight or low seed number per head,
were rapidly overcome, leading to increased
condence, farmer collaboration, and program
expansion.
L.R. DeHaan and D.L. Van Tassel, The Land Institute, 2440 E. Water
Well Rd., Salina, KS 67401; J.A. Anderson, D. Wyse, and X. Zhang, Dep.
of Agronomy and Plant Genetics, Univ. of Minnesota, 411 Borlaug Hall,
1991 Upper Buford Circle, St. Paul, MN 55108; S.R. Asselin, and D.J.
Cattani, Dep. of Plant Science, Univ. of Manitoba, 66 Dafoe Road, Win-
nipeg, MB, Canada, R3T 2N2; R. Barnes, Dep. of Ecology, Evolution,
and Behavior, 100 Ecology Building, Univ. of Minnesota, 1987 Upper
Buford Circle, St. Paul, MN 55108; G.J. Baute, Dep. of Botany, Univ. of
British Columbia, 3529-6270 University Blvd., Vancouver, BC, V6T 1Z4,
Canada; S.W. Culman, School of Environment and Natural Resources,
The Ohio State Univ., 130 Williams Hall, 1680 Madison Ave, Wooster,
OH 44691; K.M. Dorn and M.D. Marks, Dep. of Plant Biology, Univ.
of Minnesota, 250 Biological Sciences Center, 1445 Gortner Avenue, St
Paul, MN 55108; B.S. Hulke, USDA–ARS Sunower and Plant Biology
Research Unit, 1605 Albrecht Blvd. N., Fargo, ND 58102-2765; M. Kan-
tar, Biodiversity Research Centre and Dep. of Botany, Univ. of British
Columbia, 3529-6270 University Blvd., Vancouver, BC V6T 1Z4, Canada;
S. Larson, USDA ARS Forage and Range Research, 700 N 1100 E, Logan,
UT 84322; A.J. Miller, Dep. of Biology, Saint Louis Univ., 3507 Laclede
Avenue, St. Louis, MO 63130; J. Poland, Dep. of Plant Pathology and Dep.
of Agronomy, 4024 Throckmorton Hall, Kansas State Univ., Manhattan
KS 66506; D.A. Ravetta, Museo Egidio Feruglio, CONICET, Fontana
140, Trelew (9100), Chubut, Argentina; E. Rude, Dep. of Agronomy,
Univ. of Wisconsin–Madison, 1575 Linden Drive, Madison, WI 53706-
1597; M.R. Ryan, Section of Soil and Crop Sciences, Cornell Univ., 515
Bradeld Hall, Ithaca, NY 14853. Accepted 5 Jan. 2016. Received 10 June
2015. *Corresponding author (dehaan@landinstitute.org).
Published in Crop Sci. 56:1–14 (2016).
doi: 10.2135/cropsci2015.06.0356
© Crop Science Societ y of America
5585 Guilford Rd., Madison, WI 53711 USA
This is an open access article distr ibuted under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Published March 11, 2016
2 www.c rops .org crop scie nce, v ol. 56, mayjune 2016
and the potential to remedy environmental challenges in
agriculture with perennial crops (Brummer et al., 2011;
Cox et al., 2006, 2010; Glover et al., 2010). New perennial
crops for forage or biofuel could provide environmental
benets, but here we restrict our consideration to grain
crops capable of providing food directly to humans.
Although much has been written about the need for
new crops—and many new crops have been proposed—we
are unaware of a comprehensive strategy for domesticating
new crops published in the last 30 yr. Here, we will briey
review some of the older and most relevant literature. Jain
(1983) laid out systematic approaches for domesticating and
breeding new crops, and the article provides an excellent
review of domestication work and thinking in the 1970s.
More recent publications on new domestications have
focused on tree crops or energy crops (e.g., Jaenicke et al.,
1995; Leakey, 2007; Sang, 2011). New domestication has also
been addressed in a theoretical context (Diamond, 2002).
Strategy for new crop development has been approached
from a policy perspective to obtain sustained support for the
work (Jolli, 1989; Knowles, 1960). Some practical eorts
have sought to identify candidates for domestication by
determining mean values of important traits from a large
number of species (e.g., Earle and Jones, 1962; Wagoner,
1990). Others have reviewed ongoing work with a range
of potential species (McKell, 1983). However, no eort has
been made to develop a strategy based on experiences gained
in the past decade of work on new grain crop domestication
(e.g., Cox et al., 2006, 2010; Glover et al., 2010).
The reective plant breeding paradigm (Runck et al.,
2014) has been developed as a robust and potentially eec-
tive approach to developing new crops. This approach
closely couples germplasm development with coordinated
commercialization and involves interactions among sci-
entists, government, farmers, and other stakeholders to
consider not only the economic viability of a potential
new crop but also its social and environmental impacts.
This approach, developed in the context of an existing
research and development program, only identies a strat-
egy to move a single crop from domestication through
to commercialization. The paradigm does not provide
specic criteria for evaluating potential species to domes-
ticate outside of the stakeholder engagement process or
existing breeding programs nor does it provide a strategy
for prioritizing specic species in the context of limited
budgets. Ultimately, the reective plant breeding para-
digm provides a useful idealized model but lacks the prag-
matism required within a real breeding program where
certain candidates for domestication will be abandoned
as the research and development process progresses. Here,
we explicitly dene the stages and targets that domestica-
tion projects will need to go through to achieve successes.
In the past 30 yr, many species representing a wide
array of plant growth forms and taxa have been described
as candidates for domestication (Janick et al., 1996). Addi-
tionally, the list of domesticated crops has been revised to
include many more species (Meyer et al., 2012; Fuller et
al., 2010; Smith, 2006; Smith and Yarnell, 2009). Yet few
species have become viable modern crops despite initial
agronomic trials and germplasm evaluation and, often, no
publication record exists to document the work that was
done. Rather than viewing these eorts as failures, we sug-
gest that they were inevitable because the domestication
pipeline resembles the pharmaceutical one; the odds of any
given candidate having all the qualities required for full
commercialization are low. To obtain a single successful
drug (or new crop), many candidates must be screened and
rescreened, resulting in rejections at each stage of devel-
opment (Payne et al., 2007). Knowing that there will be
surprises and setbacks along the way, domesticators of new
grain crops could increase their chance of success and the
rate of new crop development by designing and following a
logical set of evaluation and development steps as they begin
and execute each domestication program. In retrospect,
aspects of the domestication pipeline have been used in our
domestication eorts over the past decade, but the model
we are proposing here has yet to be fully implemented.
The pipeline model of domestication that we propose
begins by dening an agricultural target to be met with a
type of crop that does not yet exist. In the same way, drug
development begins by dening a particular pathogen,
symptom, or disease for which current treatments are inad-
equate. A research pipeline for delivering at least one crop
that addresses the target is then conceptualized, and nally,
large numbers of wild plant species are screened and several
candidates are fed into the pipeline with the expectation
that not all will pass through to become successful crops.
Agricultural targets could include seasons where soil is left
fallow in standard crop rotations (see the pennycress case
study, below), food with enhanced nutrition, food security
in drought-prone environments, N xation in dicult soils
and climates (see the lupin case study, below), and soil con-
servation and restoration (see the perennial grain examples,
below). Additional considerations, including production
scale (e.g., subsistence vs. commodity), technology (e.g.,
mechanization, irrigation, genetic engineering), end use
(e.g., cereal, oil, animal feed or forage), and broad soil or
climatic targets, will further narrow the breeding require-
ments thereby increasing the rate of progress through the
pipeline. Once domesticated, a crop can then be bred for
adaptation to dierent environments.
In contrast to the pipeline model, a species-centric
approach attempts to nd a purpose for a preidentied,
promising, favorite, or popular plant instead of nding
a plant to meet a predened purpose. One danger with
this method is that the best niche for a particular wild
or semidomesticated plant may be already saturated. New
crops (new in the sense that farmers in a region do not
crop science, vol. 56, mayjun e 2016 www.crops.org 3
RESEARCH PHASE I: EVALUATING
CANDIDATE SPECIES
Below, we suggest criteria that can be used to evaluate
species under consideration for domestication as a grain
crop (dened as an herbaceous plant producing seeds
used for food). Evaluating species according to this list is
valuable in two ways. First, relative ranking of various
species will be helpful in selecting species for additional
investment. No unimproved wild candidate will meet all
of these criteria, but the best candidates will have some
fortuitous preadaptations or biological considerations that
reduce the number of traits requiring major modication.
Second, the relative strengths and weaknesses of a spe-
cies in relation to these criteria will inform the strategy
for domesticating that species (Phase II). We see this as a
combination of the ideas of the domestication syndrome
(Hammer, 1984) and ideotype breeding (Donald, 1968).
In addition, we see this as an opportunity to expand on
these ideas to bring new plant forms into use that were
previously missed during domestication, leveraging what
has been learned about the genetic architecture of these
characteristic phenotypes (Doebley and Stec, 1991; Gepts,
2004; Li et al., 2006a,b; reviewed in Morrell et al., 2012).
Here we will consider a number of useful criteria for
evaluating possible plants to domesticate and to use in con-
tinuous evaluation of species in the domestication pipe-
line. No candidate is expected to have all, or even many,
of these traits. Indeed, in a candidate, we are not looking
for traits at the fully domesticated level, but rather we are
looking for species with traits that will make the process
of domestication rapid and less dicult. The relative value
of each characteristic that follows would be dicult to
determine apart from evaluation of a particular candidate
species. The important consideration here is that each of
these points should be thoroughly explored and balanced
against others to determine feasibility of the eort and to
set goals before initiating a domestication program.
currently grow them), such as buckwheat (Fagopyrum escu-
lentum Moench), amaranth (Amaranthus, spp.), and spelt
[Triticum aestivum L. subsp. spelta (L.) Thell.], are annual
plants very similar in an agroecological sense to existing,
fully domesticated and high-yielding cereals. We predict
that they will struggle to attract sucient investment to
attain substantial acreage planted if a novel growth habit
(e.g., perennial or winter annual) or unique quality, such
as avor or nutrition, is not identied.
The pipeline approach diers substantially from past
screening eorts where properties of numerous species
were compared to identify the most promising candidates
(e.g., Bell et al., 2011). While these checklist approaches
are a necessary rst step, they may not be adequate to
select the species most amenable to domestication. Instead
of a one-time evaluation, we propose initiating domesti-
cation of many species and performing ongoing evalua-
tion. Each particular strength and weakness of a species is
less critical than whether an overall domestication strategy
can be developed given the strengths and weaknesses of a
species. The economic and political realities surrounding
a domestication eort are just as important to consider as
are mean values for a few key traits.
Our proposed pipeline approach proceeds in three
phases (see Fig. 1). First, a high-throughput screening
process identies promising candidates for domestication.
Second, one develops and executes a strategy to priori-
tize the research and development activities necessary to
understand, breed, and market the species. Third, the
Phase II strategies are integrated to facilitate continued
optimization. Although we briey describe this third
stage, crop improvement to optimize traits after initial
domestication (transformation from wild plant to useful
crop) is beyond the scope of this paper.
Fig. 1. Domestication pipeline. Vertical width of the narrowing pipeline depicts the relative number of species contained within. Phase I:
Screening of many plant species to discover candidates. Screening may require several cycles of selection to evaluate evolvability and
domestication potential. Phase II: Each candidate is developed according to one of three general development strategies designed to
produce a partially domesticated species usable as a new crop. Phase III: Domestication proceeds through integration of strategies to
develop a commodity crop.
4 www.c rops .org crop scie nce, v ol. 56, mayjune 2016
1. Domestic Morphology and Phenology. A prom-
ising candidate will germinate rapidly when sown,
have rapid early growth to compete with weeds, and
will be harvestable at the proper time in the target
agroecosystem. Strong candidates will also have
uniform ripening and shatter resistance, which is
conducive to mechanical harvesting at a single time
point. Moderate stature on robust stalks is useful to
prevent lodging. As an integrative measure, a plant
will be most easily used if it can be grown and man-
aged using equipment currently employed in grain
agriculture (e.g., have large, regularly shaped seed
with low or readily breakable dormancy for ease of
modern mechanical planting and harvesting).
2. Ease of Breeding and Genetics. The reproductive
biology of each species is unique, resulting in a wide
range of breeding techniques required for dierent
crops. When considering a wild species, a primar y
requirement is for knowledge of reproduction. For
instance, a species where outcrossing percentage, lon-
gevity of pollen survival, and key owering cues are
known would be preferred over a species where these
basics are unknown. If the species is self-pollinated,
easy emasculation is preferred. For making pollina-
tions, species with adequate pollen production and
accessible, long-lived stigmas are preferred. Ease of
culture in the greenhouse or amenability to counter-
season nurseries can be useful in a breeding program
to allow for multiple generations of selection, self-
ing, or crossing per year. Perennial grain crops can
provide the benet to breeding of being able to save
and propagate parental genotypes through clonal
reproduction. But perennials can be more dicult
to work with if they require a long establishment
period or several years for trait evaluation. Obtain-
ing DNA sequence information on candidate species
has become aordable; however, the actual cost and
diculty of sequencing a new species is propor-
tional to the size and complexity of the genome. An
ideal case would be a candidate species with a small,
diploid genome, in which case the development of
genomic resources for breeding is less expensive and
more tractable. As many candidate species possess
large (up to 25 Gb) tetraploid or hexaploid genomes
as a result of polyploidy or evolutionary duplication,
this should be taken into consideration as a down-
stream limitation for molecular breeding. Although
genomic information is not essential to domestica-
tion, it may be helpful in reducing the time required
for domestication from centuries to decades through
implementation of genomics assisted breeding
(Runck et al., 2014).
3. Easily Harvestable. Ease of harvest is facilitated
by seed that is large, smooth, dense, shatter resistant,
easily threshed, and winnowed without diculty.
Harvest in many systems is facilitated when the grain
is held near the end of rigid stalks that dry down
completely before harvest. For mechanized produc-
tion, the optimal plant will enable rapid harvest by
conventional equipment and with minimal loss as
a result of lodging, pod and seed shatter, or animal
predators such as birds. In subsistence production,
hand harvesting will be facilitated by seed borne in
large clusters that can be easily gathered.
4. High Yield. Yield per area is driven by two primary
factors: total biomass and harvest index. Harvest index
is the proportion of total biomass that is allocated to
the grain, and its increase has been critical to the yield
of modern cultivars (Donmez et al., 2001; Singh and
Stoskopf, 1971). Biomass accumulation is also of criti-
cal importance when evaluating a new species. Some
candidates for domestication are so small that obtain-
ing substantial grain yield will only be possible if
total biomass production is increased. Increasing total
dry matter yield has been a more important avenue to
grain yield than raising harvest index in some crops
(Tollenaar, 1989). In stressful environments, biomass
accumulation may be necessarily limited to conserve
resources and reduce premature mortality as a result
of episodic stresses found in the target environment
(e.g., frost, drought, wind).
5. Grain Similar to that of Current Crops. A new
crop will be most easily integrated into existing com-
modity markets if the properties of the new grain are
similar to a currently used crop. If avor and func-
tional attributes approximate an existing grain, the
new crop will be able to substitute for the other grain
in recipes without need for modication or a train-
ing period to adjust consumer taste preferences as has
been necessary with whole grains (Marquart et al.,
2003). Conversely, unique avors or functionality
may contribute to the development of a high-value
product (see the next point). An ideal new crop
would be easy to substitute in existing recipes while
having some features that increase its value.
6. High-Value Product. The development of a
new crop will be aided—particularly from a fund-
ing standpoint—if the harvested material can be
developed into a product of particularly high value.
Examples include suitability for special diets (e.g.,
gluten free or low glycemic index), presence of com-
pounds believed to provide health benets (e.g.,
antioxidants, omega-3 fatty acids, soluble ber), or
crop science, vol. 56, mayjun e 2016 www.crops.org 5
species with signicant genomic resources, genetic
work with the target species will be greatly facilitated.
For instance, work with either grasses or members of
the Brassicaceae is enhanced by the extensive informa-
tion available in rice (Oryza sativa L.), barley (Hordeum
vulgare L.), and Brachypodium distachyon (L.) Beauv. and
in Arabidopsis thaliana (L.) Heynh., respectively.
9. Broadly Adapted or Adaptable. To justify the
investment in domestication and commodity devel-
opment, a new crop should have the potential to be
grown on hundreds of thousands to millions of hect-
ares. Adequately testing the potential range is likely to
be dicult if a non-native species is perceived as having
the potential to become invasive or if it contains regu-
lated psychoactive chemicals. Species already widely
used for other economic purposes are particula rly attrac-
tive, since genetic resources, information about range,
reproductive biology, plant nutrition, pathology, and
an international history of noninvasiveness are likely
to be available. Ecogeographical approaches (e.g., Li et
al., 2013) could be useful to identify potential regions
of adaptation for new domesticates. When considering
climate change, species that will be more resilient to
uncertain weather patterns may be preferred.
10. Low Input Requirements. New crops that can be
grown with minimal pesticide, irrigation, tillage, fer-
tilizer, and weed control will be attractive to farmers
for economic and conservation reasons. While any
productive crop will require adequate moisture and
fertility, there is particular need for crops that can
tolerate periodic water shortages, use resources more
eciently, x N symbiotically, access stored soil mois-
ture, and remain free of pests and diseases through
resistance or competitive ability. Low input require-
ments open the possibility of marketing new crops as
specialty organic crops, which could potentially allow
organic premiums to balance out lower initial yields.
11. Enhanced Ecosystem Services. Crops that can
provide ecosystem services are more likely to attract
funding for development, and their adoption may
be facilitated by value placed on ecosystem services
either by consumer choice or government support.
Examples of ecosystem services that may be provided
by new crops include soil C sequestration, habitat for
wildlife (including pollinators), biocontrol of pests
through habitat for natural enemies, and clean water
by the prevention of runo and nutrient leaching. As
support for multifunctional agriculture increases and
valuation methodology matures, crops that provide
enhanced ecosystem services beyond provisioning
grain will have an advantage.
perceived benets of the crop to areas such as sus-
tainability or wildlife conservation. If the harvested
product is visually distinct from other existing grains
or produce, identity preservation in postharvest mar-
keting will be considerably easier.
7. High Nutrition and Quality Attributes. A new
food crop will most easily enter the market if consum-
ers are condent that the food is safe for consumption.
New crops with no known toxic intrageneric rela-
tives are more likely to be safe than those related to
highly toxic species. Likewise, if the crop has been
historically eaten or is a close relative of a widely con-
sumed crop, the likelihood of the grain being safe to
eat is dramatically higher (Smartt, 1990), and if the
species has been used in wide hybridization with cur-
rent crops (Wul and Moscou, 2014), companies will
be more condent in marketing products containing
the new grain without fear of liability from toxicity.
Many current crops require processing to render them
edible, but a new crop will be more protable and
will easily enter the market if special processing is not
necessary. Crops such as rapeseed (Brassica napus L.)
(Bell, 1982) were initially unpalatable for human and
animal consumption but were made edible through
selection for canola-quality oil. Although toxins may
be bred out of most plants, breeding for edibility can
be expensive. The cost of developing canola from
rapeseed was about $95 million in 2014 US dollars
(Bell, 1982). If necessary, a potential route may be
rst the adoption of candidate species as industrial or
feed crops to build breeding resources, and second,
funding for the development of food quality grain as
happened with canola (McVetty and Scarth, 2002).
8. Available Genetic Resources. Abundant germplasm
collections will facilitate the domestication of a species.
Easily accessible wild populations can also be a good
resource, but populations present primarily in inac-
cessible regions because of political reasons would be
dicult. The size of the secondary gene pool (number
and accessibility of closely related species) should be
considered along with any factors that make it dicult
to exploit genetic resources such as apomixis or lack
of genomic stability. The low cost of whole-genome
sequencing enables one to identify the complete gene
space of any organism and make predictions about
which genes might be targets for future improvement.
If the species is a diploid with low gene redundancy,
mutation breeding approaches can be used to identify
benecial mutations in the target genes (Sedbrook et
al., 2014). These approaches will be especially ame-
nable if the candidate species propagate primarily
through self-fertilization. If there is a closely related
6 www.c rops .org crop scie nce, v ol. 56, mayjune 2016
12. Cu lturally Tenable. Traditional indigenous territo-
ries encompass up to 22% of the world’s land surface
and coincide with areas that hold 80% of the planet’s
biodiversity (Sobrevila, 2008). Despite this, the bene-
ts of this biodiversity are disproportionately realized
by the wealthy: 97% of patents worldwide are held by
individuals and companies in industrialized countries
(United Nations, 1999). Careful attention should
be paid to equity and cultural issues when selecting
candidate crops. Specically, wild species that are
important to a people group should not be domesti-
cated without the express consent and collaboration
of those people. For further discussion of this topic,
see the case study on wild rice, below.
13. Knowledge of the Candidate’s Disease and Pest
Risk. Knowledge of a species’ major diseases and
insect pests will help to accelerate a domestication
program because basic research to understand major
limiting biotic factors can be a costly and lengthy
endeavor before the species can be grown success-
fully in breeding nurseries. Potential of the species
to become invasive in a particular region is a critical
consideration. Relatives of existing crops or species
grown widely for horticultural purposes will likely
have a wealth of existing biological information. In
contrast, obscure species from genera with no cur-
rently used plants will present a greater challenge.
14. Low Potential to Become Invasive or Con-
taminate the Gene Pool of a Native Species.
Invasiveness is a concern primarily with exotic species
being domesticated for use outside their native range.
Conversely, domestication of native species could
increase the frequency of rare domestication alleles,
which could then ow into the wild populations.
Although domestication for use as a grain will likely
reduce invasiveness by reducing seed dormancy, dis-
persal, and plant height (Nentwig, 2007), potential for
invasiveness could limit early work with the species.
Species projected to become invasive by predictive
approaches (e.g., Mack, 1996; Pheloung et al., 1999)
should not be introduced for domestication. Partially
domesticated species may pose the greatest risk of inva-
siveness because early selections may increase vigor and
seed production before xation of traits, such as non-
shattering, that will reduce invasive risk. During this
period of semidomestication, the populations should
be closely monitored for invasive potential and grown
in limited locations. When domesticating a native spe-
cies, genetic pollution of remnant populations may be
reduced by not growing the domestic plant forms near
critical remnant populations.
RESEARCH PHASE II: WILD SPECIES
TO NEW CROP
Every candidate for domestication will have a unique blend
of strengths and weaknesses, but here, we suggest three
primary strategies. For each candidate, a custom set of
domestication milestones should be dened based on one,
or a combination, of the three strategies below. Failure to
meet the initial goals should trigger a thorough reevaluation
of the candidate or shifting of resources to other candidates.
We will describe each of these strategies in turn and pro-
vide examples of their use in the case studies that follow.
1. Address the Primary Limitations. Potential
domesticates often have traits that limit viability of the
crop or hinder breeding progress. These traits have
been termed crucial domestication traits (Abbo et al.,
2014). Among these are severe shattering, a seed coat
that is impermeable to water (hard seed), very dicult
threshing, severe lodging, and presence of toxins, or
antiquality factors. Less obvious traits include complex
germination requirements and poor seedling vigor,
invasive spreading, or extreme height and plasticity.
These restraints may need to be solved quickly because
they make large-scale experiments or use as food
almost impossible. The rst step in addressing these
limiting factors may be to obtain numerous collections
and search for rare individuals with allelic variation to
overcome the limitations. There is the possibility of
conducting forward genetic screens if variability is not
apparent in wild collections, with programs in muta-
genesis, TILLING (Targeting Induced Local Lesions
IN Genomes), ecoTILLING, or rapid cycling of strict
selection cycles for the critical traits could be initiated
(Till et al., 2006). Alternately, severe limitations such
as dicult establishment, lodging, or stand decline in
perennials may be readily overcome through physi-
ological or agronomic studies. Perhaps the plant will
be poorly adapted for grain production in the rst test
region but may succeed in other environments. If pri-
mary limitations cannot be overcome after making
a substantial eort, resources could more wisely be
directed toward other candidate species.
2. Build on Strengths. If the target species has particu-
lar strengths, as revealed in the evaluation above, these
should be exploited to attract funding and research sup-
port to develop the crop. If the species has potential as a
specialty crop, this aspect could be highlighted through
product development and small-scale production to
create market pull. If the grain has properties similar
to existing commodities, then food science research to
highlight the large potential market should be priori-
tized and initiated. When there is a close relative with
extensive genomic resources, reverse genetic approaches
crop science, vol. 56, mayjun e 2016 www.crops.org 7
facilitated by sequencing the species may be an obvious
choice to attract additional research support as was done
with pennycress (Thlaspi arvense L.) (Dorn et al., 2015).
In the case of crops with potential to provide expanded
ecosystem services, documenting those services could
be an important early research objective, as has been
done with intermediate wheatgrass [Thinopyrum inter-
medium (Host) Barkworth & D.R. Dewey] (Culman
et al., 2013). Another strategy may be to develop a by-
product market, such as forage or biofuel, to expand
market potential, garner research support for the crop,
and develop transition strategies into new markets.
3. Breed to Improve Quantitative Traits. In the
absence of clearly limiting factors or obvious strengths
to build on, primary attention should be given to
important traits with quantitative control. In many
cases, low grain yield (and its components) is the quan-
titative trait that should receive primary attention.
Grain yield in current domestic grains has risen steadily
over many decades, with the highest rates of increase
in the United States of £2.4% yr−1 (Ray et al., 2013).
Harvestable yield may quickly increase through the
use of a particular mutation as seen in strategy number
one above. But in general, high yield will be attained
through an incremental process of evaluation and selec-
tion that will result in small but steady increases. If
yields have to increase by two- to vefold for a wild
plant to become viable domestic grain, at least a decade
or more of breeding work will generally be required.
In this case, breeding can proceed for many years to
increase yield before beginning commercialization
or utilization research. In the case of perennial grain
crops, genomic selection may be particularly useful for
accelerating progress (Hener et al., 2010).
PHASE III: FROM NEW CROP
TO COMMODITY CROP
For those species passing the second phase and progressing
to a full new-crop domestication program, aspects of all
three strategies will eventually be integrated. In Phase III,
recurrent selection for yield and other quantitative traits
will be necessary to develop a broadly grown crop. How-
ever, we predict that most domestication candidates would
also benet from a regular reassessment along the lines of
Strategies 1 and 2 (Phase II, above). Having made progress
on the most serious limitation, it is critical to determine
the next single most-limiting trait. Perhaps an intense
eort is necessar y to overcome that limitation and then to
introgress the improvement into the elite lines or popula-
tions from the yield improvement program. Likewise, it
will be helpful to periodically engage key stakeholders to
ensure that germplasm development is coordinated with
enterprise development (Runck et al., 2014).
Case Studies: Lessons Learned
Illinois Bundleflower: Severe Primary Limitations
For several decades, the Land Institute and other institu-
tions have studied and worked toward the domestication
of the herbaceous perennial legume Illinois bundleower
[Desmanthus illinoensis (Michx.) MacMill. ex B.L. Rob. and
Fernald]. This species attracted attention as a potential grain
because of its soil-conserving perennial root system, sym-
biotic N xing ability (Beyhaut et al., 2006), and high seed
production relative to other perennial herbaceous species
(DeHaan et al., 2003; Kulakow et al., 1990). Research-
ers identied abundant genetic variation for traits, such as
seed size and yield (DeHaan et al., 2003), and even found
a genetic solution to shattering. However, work with this
species has been frustrating for a number of reasons. First,
it is a dicult species to breed as a result of its small ower
parts, partial selng, challenging emasculation, and di-
culty growing in standard greenhouse conditions. Second,
the seed has an objectionable avor, and safety for use as
a human food has been dicult to demonstrate. Finally,
the roots of Illinois bundleower contain the regulated
substance N,N-dimethyltryptamine (Halpern, 2004),
raising questions about the legal regulations surrounding
seed production and sale of this species. Work with Illinois
bundleower has mostly been placed on hold because these
primary limiting factors were never addressed adequately.
Before renewing domestication eorts with this species,
the primary limitations listed here must be addressed.
Learning from work with Illinois bundleower, domesti-
cation programs should attempt to remedy severe primary
limitations before advancing to other eorts. If the pri-
mary limitations cannot be solved quickly or eciently,
then resources would be better allocated to other species.
Maximilian Sunflower: Target
Environment Mismatch
Decades of research have also been directed toward the
herbaceous perennial sunower (Helianthus maximiliani
Schrad), which is native to most of North America. The
species has high yield potential and genetic variation for
seed size and head size (compared with other wild peren-
nials). As a perennial grain, the species was expected to
provide edible vegetable oils and reduce erosion, runo,
and input costs. With conventional breeding, selection for
yield and seed size has been successful. A breeding popula-
tion in 2012 has seeds that are on average 2.4 times larger
than the unselected germplasm evaluated in 2002 (Van
Tassel et al., 2014). Mechanical harvest is dicult because
heads are produced at multiple heights and stalks are tall and
tough, requiring very slow ground speed when harvesting
mechanically. Populations with apical owering have been
8 www.c rops .org crop scie nce, v ol. 56, mayjune 2016
developed to address ease of harvest and synchronicity of
maturation (Van Tassel et al., 2014); however, reducing
the number of heads per stalk reduces the yield and large
increases in head size will be required to compensate.
Yield decline and drought sensitivity have been found
to limit production and complicate selection for yield
potential in central Kansas (D.L. Van Tassel, unpublished
observations). So far, we have not been able to identify
a rapid selection protocol or management tool to over-
come these limitations. However, this species is amenable
to greenhouse cultivation (D.J. Cattani, S.R. Asselin,
unpublished observations) and is a member of a genus with
rich genomic resources, suggesting that genomic assisted
methods could perhaps overcome these obstacles in the
future. In retrospect, it was a mistake to assume that the
target agricultural range overlapped the full native range
of the species; it tolerates dry periods through wilting, leaf
abscission, and reduced growth and owering responses
that ensure survival but not reliable seed yield in the spe-
cies’ southern range. Targeted initial studies with this spe-
cies should have identied yield stability in southern loca-
tions as a major limitation. The next step should have been
identifying climatic conditions or management strategies
that overcome or avoid this limitation. Unless simple,
inexpensive management solutions had been quickly iden-
tied, the kind of recurrent candidate ranking proposed
here would likely have deprioritized the domestication
of this species for unirrigated, drought-prone environ-
ments because redesigning a species’ drought response is
a formidable additional breeding objectives that can only
slow breeding progress for yield. However, in Manitoba,
yield declines and summer drought stress have not been
observed (D.J. Cattani, S.R. Asselin, unpublished obser-
vations). These observations illustrate the importance of
matching the target agricultural environment with the
strengths and limitations of the domestication candidate.
Weeping Rice Grass: Weak Support
for Agricultural Target
The native Australian weeping rice grass [Microlaena stipoides
(Labill.) R. Br.] has been under consideration and experi-
mentation for use as a resource-conserving perennial grain
for more than a decade (Davies et al., 2005). Davies et al.
(2005) suggested that determining the edibility of weep-
ing rice grass would be an important step toward its use
as a perennial grain crop. The authors also stressed the
importance of yield. However, there is no indication that
projects were ever initiated to breed for yield or determine
whether antinutritional factors are present in the grain.
Indeed, 9 yr later, low yield remained a primary limita-
tion to using weeping rice grass as a grain (Malory, 2014).
We interpret the initial lack of progress as evidence that
the species was proposed as a domestication candidate with-
out adequate support for the agricultural target in mind,
that is, improving sustainability by developing a perennial
grain. Thus, Strategy 1—solving the issue of edibility—and
aggressively breeding for increased yield (Strategy 3) were
left unfunded. Recent work with weeping rice grass took
advantage of the genomic information available in rice, a
related species. Mutagenesis combined with sequencing and
genomic comparison to rice has been used to identify can-
didate alleles to be used in domestication (Shapter et al.,
2013). Whether this advancement strategy can be used to
develop high-yielding varieties remains uncertain.
Perennial Chickpeas: Target
Environment Mismatch
Several perennial Cicer spp. have been collected and are
available from the USDA–ARS. Data on potential for
domestication has been collected on 23 accessions from
eight species (Watt et al., 2005). The relatively large seeds
of some accessions suggested potential for domestication
as a perennial pulse crop (i.e., grain legume). All of the
accessions evaluated had seed shattering and pod shedding.
These traits, along with soft seededness, would be among
the rst to address if a domestication program were initi-
ated. When perennial Cicer spp. were evaluated in Kansas,
indeterminate owering and low survival (possibly as a
result of disease) made the plants challenging to evalu-
ate, and a breeding program was never initiated (L.R.
DeHaan, unpublished observations). In other words, this
group of species was screened out for use in the central
United States primarily on the basis of high mortality and
dicult harvest in the target environment. If a program
were initiated with this species, disease resistance, seed
shattering, and pod shedding are major limitations that
should receive primary attention.
Case Studies: Successes and Current Efforts
American Wild Rice: Building on Consumer
Demand, Displacing an Indigenous Economy
Since prehistoric times, the wild annual grass manoomin
(wild rice; Zizania palustris L.) has been harvested from
naturally occurring stands by Native Americans. Domes-
tication of wild rice began in the rst half of the twenti-
eth century, with initial investigation done by European–
American farmers who later asked the University of Min-
nesota to domesticate the species. University of Minne-
sota involvement led to genetic and agronomic advances,
with manoomin eventually becoming an established crop
(Oelke, 1993). The major genetic change that allowed
increased cultivation of paddy rice was shatter resistance,
rst discovered in 1963, which resulted in an immediate
10-fold increase in harvestable wild rice yield in paddy
rice systems and led to a 100-fold increase in Minnesota
on-farm production over the next 20 yr (Oelke, 1993).
However, from the perspective of the Anishinaabe
nations of Minnesota, the scientic investigation of
crop science, vol. 56, mayjun e 2016 www.crops.org 9
manoomin (wild rice) was done in an exclusionary manner.
It was noted that, “virtually all wild rice research emerging
from the University of Minnesota has reected the goals and
desires of non-Indians with little regard for Native Ameri-
can concerns, perspectives, or the considerable store of tra-
ditional knowledge of manoomin” (Andow et al., 2011).
The research has been labelled biopiracy because germplasm
was taken from tribal nations with little or no consultation,
was developed into a commercial product with little or no
tribal nation involvement, and resulted in little or no rev-
enue from the resultant crop to tribal nations.
Manoomin is vital to the perpetuation of Anishinaabe
culture and identity, with this connection having developed
over thousands of years of coexistence with the plant. Their
domestication paradigm diers radically from the Western
one and is derived from a dierent knowledge system, that
is, harvesting the plant should domesticate people rather than
people domesticating the plant. The tribes perceive their role
as keen observers and active agents in responding to the con-
ditions of the plant rather than changing those conditions.
Anishinaabe communities are deeply concerned
about the labeling of marketed manoomin to distinguish
between traditional grain produced in its native habitat
and domesticated grain produced commercially in pad-
dies. Tribal natural resource departments are interested in
collaborative research that would benet their community
and preserve wild rice in its natural habitat. Without par-
ticipation, research is viewed by the minority community
as disrespectful, exploitative, a form of colonization, and a
violation of treaty rights. However, strides have been made
in this regard, with three large-scale meetings between
Anishinaabe and the University of Minnesota held over the
last 6 yr. Progress has been made toward a memorandum
of understanding regarding research on wild rice (Nibi and
Manoomin: Bridging Worldviews Committee, 2014).
Early commercial paddy production of wild rice
succeeded because of one particular strength—willing
buyers. Consumer demand has been strong based on its
avor, texture, and nutritional benets (Cho and Kays,
2013). Wild rice illustrates how early production can use
a strength (in this case consumer demand) to attract the
research required to overcome a primary limitation (in
this case seed shattering). In contrast, shattering was a
characteristic valued by Indigenous communities in tra-
ditional wild rice production systems for reseeding and
maintenance of genetic diversity. This domestication case
study reveals domestication breeding as a sharp but dou-
ble-edged sword capable of rapidly transforming a wild
species to create a new crop and at the same time under-
mining a preexisting culture and economy based on the
harvesting of wild populations. In the future, wild species
that are economically important to a people group should
not be considered as candidates for domestication without
the express consent and collaboration of those people.
Sweet White Lupin: Target Environment Match
Lupin production in Australia is based primarily on the
annual leguminous species Lupinus angustifolius L., which was
developed as a new crop in the 1960s. The crop’s genetic his-
tory has been recorded by Cowling and Gladstones (2000),
and we will summarize their work below. As reported,
other lupin species were considered for domestication in
Australia, but they suered from drought stress, poor adap-
tation to local soils, late maturity, or susceptibility to disease
and insects. Lupinus angustifolius was selected based on its
vigorous growth and the presence of critical mutant types.
Semidomesticated forms (each possessing some domestica-
tion traits but lacking others) were introduced from Europe,
but fully domesticated plants were developed by identifying
and stacking several rare alleles for early owering, shat-
ter resistance, soft seed, white owers and seed, and low
alkaloid content. In the early years of lupin production, the
diseases grey leaf spot [Stemphylium vesicarium (Wa l lr.) E .G.
Simmons] and Phomopsis stem blight (Diaporthe toxica P.M .
Will.) severely limited production. Discovery of resistance
genes and the release of resistant cultivars were critical to
the expansion of lupin production.
Marsh et al. (2000) have reported on the factors inu-
encing lupin production and expansion in Western Aus-
tralia, and we will summarize their work here. The rst
fully domesticated cultivars resulted in rapid adoption, with
120,000 ha planted in 1973. Droughts and poor management
practices caused declining yields, and planted area had fallen
to 40,000 ha in 1978. In 1979, a new higher-yielding variety
was released, and a major extension eort was initiated to
demonstrate that successful cropping of lupin was possible.
The new agronomic package of improved varieties, higher
planting density, earlier planting, and eective weed control
was successful. By 1987, planted area peaked at 877,000 ha.
In summar y, the decision to invest in lupin was based on
its ability to x N and produce high-protein animal feed in
an environment where fully domesticated grain legumes had
been unadapted because of the Mediterranean climate and
poor soils. Success of lupin as a crop depended on breeding
for key domestication traits followed by agronomic research
and extension to help producers grow the crop successfully.
A postscript to this story is that lupin production in
Australia has been declining in recent years. Marketed as an
animal feed, the export price is lower than soybean [Glycine
max (L.) Merr.], which produces both feed and oil. Many
farmers have replaced lupin with canola in their rotation
because of better weed control options and fewer fungal
diseases. New disease- and herbicide-resistant lupin lines
are being developed. Perhaps somewhat belatedly, building
on evidence of health benets, Western Australia is invest-
ing in food product development to increase the value of
lupin grain (Peterson and Wilkinson, 2014). This example
suggests that developing high-value end uses may be a stra-
tegic investment to ensure long-term new-crop viability.
10 www.c rops .org crop scie nce, v ol. 56, mayjune 2016
Field Pennycress: Excellent
Primary Characteristics
Pennycress (Thlaspi arvense L.) is a potential winter annual
oilseed crop being developed in the US Midwest for use
as a cover crop and biodiesel feedstock. Domestication of
this species is an example of building on strengths within
a wild species. The rst strength is derived from the plant’s
phenology. Its exceptionally short lifecycle and cold toler-
ance allows it to be grown successfully over the winter
within the corn–soybean rotation. Although a pennycress
cover crop has been shown to reduce soybean yield, the
combined pennycress and soybean yield has been greater
than soybean alone (Johnson et al., 2015). Not only
does the crop have potential to increase farmer incomes
through increased total oilseed yield, a pennycress cover
crop could also improve soil and water quality, although
this remains to be shown experimentally.
The second strength that pennycress has comes from
its small genome and close relationship to the model species
A. thaliana (Sedbrook et al., 2014). With modern sequenc-
ing techniques, the transcriptome of several pennycress tis-
sues and a draft genome have been assembled (Dorn et al.,
2013, 2015). Comparative analysis with A. thaliana allowed
identication of orthologs that may control critical traits
such as owering time and glucosinolate metabolism. With
these genomic tools, breeding of more adapted types of
pennycress with seed suitable for animal or human con-
sumption should be possible (Dorn et al., 2015).
Silphium: Good Agricultural Target,
Overcoming Primary Limitations
The herbaceous perennial species Silphium integrifolium
Michx. is native throughout the central United States.
Eorts to domesticate this species as a perennial grain crop
are ongoing, and are described by Van Tassel et al. (2014).
Two strengths made the species particularly attractive: large
seed and drought tolerance. Seed mass of 21 mg has been
reported (Kowalski and Wiercinski, 2004), and S. intergri-
folium is among the most drought-tolerant plants found in
the North American prairie (Weaver et al., 1935). Silphium
integrifolium was selected for domestication over its relative,
S. laciniatum, because the latter develops more slowly and
may not ower until the third year after planting.
The most obvious breeding target to raise grain yield
in S. integrifolium was to increase the number of ray o-
rets (the only orets that produce a seed) per head. Selec-
tion on this easily measured trait was expected to induce
a more rapid response in yield potential at lower cost than
complex yield measures (DeHaan and Van Tassel, 2014).
More than 10,000 individuals were evaluated for ray oret
number in 2006. The average number of ligules per head
(a proxy for ray orets per head) was estimated to be 28
to 30, and 83 plants with 38 or more ligules were selected
for intermating. Polycross progeny were established the
next year, and the selection procedure was repeated for
two more cycles. In 2012, the average number of ray o-
rets per head was 52, and some plants had >100 ray o-
rets. One plant had >150 ray orets per head (Van Tassel
et al., 2014). Having addressed the problem of low seed
number per head, the program at the Land Institute has
since moved on to additional germplasm collection and
evaluation and selecting for yield per stalk, mass per seed,
and fatty acid prole. Silphium integrifolium provides an
excellent example of using cost-eective recurrent selec-
tion for several years to solve a major limiting factor in a
potential domesticate (Strategy 1) before moving on to
broader-scale work with the species.
Intermediate Wheatgrass: Good Primary
Characteristics, Early Market Potential
Researchers at the Rodale Institute selected the peren-
nial intermediate wheatgrass T. intermedium as a target for
domestication as a grain crop after evaluating nearly 100
species based on the following traits: vigorous perennial
growth, good avor, easy threshing, large seed, synchro-
nous seed maturity, shatter resistance, lodging resistance,
and ease of mechanical harvest (Wagoner, 1990). Vigorous
perennial growth was considered an essential trait in this
instance because the primary objective was to develop a
plant that would provide the ecosystem service of erosion
control. In collaboration with USDA–NRCS scientists at
the Big Flats Plant Materials Center, two cycles of selection
for a broad index of traits were performed. Because the
species was partially domesticated through these eorts, no
trait was seen as an outstanding strength or weakness when
the Land Institute began work with the species in 2001.
Since 2003, phenotypic recurrent selection based
mainly on yield and yield components (mass of seed per
head and mass per seed) has been performed at the Land
Institute. As reported by DeHaan et al. (2014), after two
generations, seed mass had increased over the starting
material by 23%, but yield per land area in solid seeded
plots responded more quickly, increasing by 77%. If these
gains continue in a linear fashion, yields similar to wheat
(Triticum aestivum L.) currently grown in Kansas would
require another 20 yr of breeding. Because seed mass is
responding more slowly, about 110 yr would be required
to achieve a seed mass of 30 mg seed−1. To address mass per
seed directly, mass selection was performed on individual
seed weight for eight generations. Over this time, mass per
seed increased by 0.52 mg seed−1 generation−1. If progress
continues in a linear fashion, another 44 yr of selection will
be required to achieve a seed mass of 30 mg seed−1. These
extended timescales underscore the importance of initiat-
ing large-scale selection programs to improve important
quantitative traits in new domestication programs.
When improved intermediate wheatgrass germplasm is
grown in northern environments, grain yields exceeding 150
crop science, vol. 56, mayjun e 2016 www.crops.org 11
g m−2 can now be obtained on experimental plots (DeHaan
et al., 2014; Culman et al., 2013). These promising yields have
led to the rst commercial plantings of the grain with small-
scale marketing under the name Kernza. Yield and com-
mercial interest have attracted support for additional work in
important areas such as milling and baking quality (Zhang
et al., 2014) and molecular genetics (DeHaan et al., 2014).
Using genotyping-by-sequencing, genome-wide markers
are available for intermediate wheatgrass. With maturity
of the breeding program, genome-wide prediction is being
introduced to accelerate the domestication of intermediate
wheatgrass by increasing the selection eciency and short-
ening the selection cycle (Zhang et al., 2016). While an all-
around excellent target for domestication and improvement,
the large polyploid genome (~13 Gb) makes the implemen-
tation of genomics-assisted breeding challenging. Breeding
objectives are now being broadened to include traits such
as lodging resistance, shatter resistance, and free threshing
ability. Furthermore, agronomic studies are in progress to
identify methods of enhancing and sustaining yield with low
inputs and documenting potential ecosystem services from
the crop (Culman et al., 2013).
In summar y, the intermediate wheatgrass domestica-
tion eort provides a good example of starting with a gen-
erally promising species that provides valuable ecosystem
services and using phenotypic selection sustained over a
decade to increase yield (Strategy 3) to the point where
the crop is worthy of additional research investment.
More recent work has built on the strength of a grain with
qualities somewhat similar to wheat and genetic variabil-
ity that may allow development of varieties for specic
types of products (e.g., bread, pancakes, beer) and blend-
ing with wheat (Strategy 2).
CONCLUSIONS
Modern domestication is an economic and political activity
as much as a biological one. In an era of xed or con-
tracting public investment in plant genetics, tradeos are
inescapable; more time and eld space devoted to one can-
didate likely means less allocated to others. Here, we have
attempted to develop an economically rational approach to
new domestications that (i) reduces the amount of research
and development required to bring a new crop to full com-
mercialization by prioritizing wild plants with fortuitous
preadaptations (e.g., large seeds), (ii) reduces wasted eort
by quickly screening out candidates with insurmountable
risk factors, (iii) strategically allocates early investments to
increase a project’s appeal to additional investors and col-
laborators, and (iv) simultaneously lays the foundation for
sustained gains in yield and marketability.
Plant domestication eorts should begin with an agri-
cultural target in mind. That is to say, the domestication
eort should be performed to meet a particular need or
solve a problem in a unique way. Then, various species
should be evaluated and experimented with to eventually
develop at least one new crop species that addresses the
perceived needs. This approach contrasts with eorts that
begin with a particularly interesting species and seek to
nd ways to make that species useful or protable.
The species ranking and screening process described
in Phase I is partially a deductive and descriptive process.
It may be possible to score plants for many of the attributes
listed using herbarium specimens, species monographs,
etc. Specialists accustomed to collecting and growing wild
or partially domesticated plants, including indigenous
communities, ornamental and forage breeders and deal-
ers, native vegetation restorers, or botanical garden cura-
tors, can suggest candidates with agronomic growth form,
high vigor, adaptation to a particular environment, etc.
Preliminary empirical research is likely to be necessary,
at least in some cases, to obtain estimates on traits such
as seed dormancy, seedling vigor, seed nutrient content,
or edibility. These studies should not only evaluate varia-
tion between species and populations, but also screen the
diversity within populations and collections.
However, evaluation of candidates will never be com-
pleted by surveying species and their mean or range of
values for various traits. Only by initiating selection pro-
grams will domesticators be able to fully evaluate the rela-
tive potential of various species. Once species are in the
domestication pipeline, ranking species by their potential
becomes feasible.
Phase II should be seen not only as an opportunity
to strategically improve the candidate to make it easier to
fund and work with, but also as an opportunity to test its
ability to respond to intense directional selection. Even
where this is not an explicit part of the strategically highest
priority research, we suggest that some selection be initi-
ated. For example, even in the cases where it makes sense
to rst focus resources on projects such as validating a food
crop’s reputed antioxidant content, on designing harvesting
machinery, or on optimizing agronomic practices, single-
trait recurrent selection experiments could be performed
with minimal cost or labor requirements as described above
for increased numbers of seeds in S. integrifolium heads
and seed mass in intermediate wheatgrass. In addition to
making progress on an important trait, the exercise is likely
to result in innovations in protocols for growing, crossing,
harvesting, phenotyping, etc. These practical insights will
be needed for Phase III, when, funding-permitting, the
domestication process will be scaled up.
Even in cases for which it is necessary to drop candi-
dates from the pipeline, eorts should be made to catalog
and disseminate the eorts undertaken. Given the time
and expense of development eorts, as well as the poten-
tial for the same or similar species to be independently
reconsidered later, even negative results should be viewed
as important ndings.
12 www.c rops .org crop scie nce, v ol. 56, mayjune 2016
Finally, to justify the large investment required to
domesticate a wild plant species, there must be a reasonable
chance for it to be successfully grown over extensive areas
for many years. For that to happen, it must displace exist-
ing alternate crops on some landscapes. This requires the
new crop to be more protable, which implies both ade-
quate yields and some advantage in grain quality, reduced
inputs, coproduct values, or ecosystem services. Although
many candidates could have this biological potential, few
will have both traits that make them appealing to plant
breeders and the potential for initial use as new specialty
crops that will bootstrap their own later stages of domesti-
cation. Furthermore, even a promising species will require
genetic or genomic resources to permit rapid deployment
of new cultivars to adapt to changing climate, pests, and
markets (Gur and Zamir, 2004; Hoisington et al., 1999;
Varshney et al., 2012). For these reasons we have proposed
criteria and strategies to help breeders dispassionately eval-
uate candidates at early stages in the domestication pipe-
line, advancing only the most promising candidates for
additional investment.
Acknowledgments
This paper was inspired by the Domestication Group discus-
sions at the “New Roots for Ecological Intensication” meet-
ing held 27–31 Oct. 2014 in Estes Park, CO. The authors are
grateful to Melinda Merrill and the Estes Institute for sponsor-
ing and hosting the meeting. They also gratefully acknowledge
the helpful critiques received from ve anonymous reviewers.
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... The grain yield was very small in the first year but increased to 33% of the wheat in the second year and with a harvest index of 0.1. The progress of selection in kernza is described in DeHaan et al. (2016). Two generations of recurrent selection increased seed mass by 23%, and yield per land area in solid seeded plots by 77%. ...
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... During cultivation, plants have been selected for improvements in yield and harvestability [45]. Other traits, such as seed color and fruit color [30,31], the balance between dormancy and germination [32], taste profile [46,47], and adaptability to the environment [48], are also constantly under conscious selection by breeders and consumers. ...
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