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Crops gone wild: Evolution of weeds and invasives from domesticated ancestors


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The evolution of problematic plants, both weeds and invasives, is a topic of increasing interest. Plants that have evolved from domesticated ancestors have certain advantages for study. Because of their economic importance, domesticated plants are generally well-characterized and readily available for ecogenetic comparison with their wild descendants. Thus, the evolutionary history of crop descendants has the potential to be reconstructed in some detail. Furthermore, growing crop progenitors with their problematic descendants in a common environment allows for the identification of significant evolutionary differences that correlate with weediness or invasiveness. We sought well-established examples of invasives and weeds for which genetic and/or ethnobotanical evidence has confirmed their evolution from domesticates. We found surprisingly few cases, only 13. We examine our list for generalizations and then some selected cases to reveal how plant pests have evolved from domesticates. Despite their potential utility, crop descendants remain underexploited for evolutionary study. Promising evolutionary research opportunities for these systems are abundant and worthy of pursuit.
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Crops gone wild: evolution of weeds and invasives
from domesticated ancestors
Norman C. Ellstrand,
Sylvia M. Heredia,
Janet A. Leak-Garcia,
Joanne M. Heraty,
Jutta C. Burger,
Li Yao,
Sahar Nohzadeh-Malakshah
and Caroline E. Ridley
1 Department of Botany & Plant Sciences and Center for Conservation Biology, University of California, Riverside, CA, USA
2 Irvine Ranch Conservancy, Irvine, CA, USA
3 United States Environmental Protection Agency, National Center for Environmental Assessment, Arlington, VA, USA
Since the advent of agriculture humans have encountered
plants that have frustrated their goal to manage their
environment. Today, we call the plant pests that interfere
with agriculture ‘weeds’. In the last few centuries, humans
have taken an increasing interest in preserving and other-
wise maintaining the biodiversity of more ‘natural’ [i.e.,
‘less managed’ (Kaus and Go
´mez Pompa 1992)] commu-
nities. Here, too, plant pests frustrate human intentions.
In such situations, these plants are called ‘invasives’.
Weeds and invasives are problematic plants at ends of a
continuum of how intensively humans manage an ecosys-
tem, with manicured lawns and cultivated croplands at
one end, through forest plantations and rangelands, to
natural, deliberately lightly managed, areas at the other
end. Thus, the distinction between weeds and invasives,
though often clear, is occasionally fuzzy or arbitrary.
Some plants can become weeds and/or invasives with
the appropriate ecological opportunity (e.g., colonizing a
region where their primary predator is absent) and with-
out any genetic change. But an increasing body of
research has revealed that some plants have evolved to
become pests. Following the publication of the book, The
Genetics of Colonizing Species (Baker and Stebbins 1965),
evolutionary biologists began to focus on how weeds
might evolve (e.g., Baker 1974; de Wet and Harlan 1975;
Barrett 1983). The idea of evolution as a potential route
to invasiveness has become rapidly accepted in the last
two decades, not only for plants, but also for animals
and microbes (Blossey and No
¨tzold 1995; Ellstrand and
Schierenbeck 2000; Arnold 2006; Novak 2007; Prentis
et al. 2008; Schierenbeck and Ellstrand 2009).
With the goal of understanding whether and how
weediness and invasiveness evolve, empirical studies are
accumulating that compare problematic lineages with
their putative ancestral populations, in plants as well
as other organisms (Bossdorf et al. 2005; Dlugosch and
Parker 2008a). Some of these studies compare genetic
marker variation, often identifying changes in diversity
and population genetic structure. Other descriptive
studies compare phenotypic or ecological differences
de-domestication, domesticate, endoferality,
exoferality, hybridization, invasive species,
rapid evolution, weed.
Norman C. Ellstrand, Department of Botany &
Plant Sciences and Center for Conservation
Biology, University of California, Riverside, CA
92521, USA.
Tel.: 1-951-827-4194; fax: 1-951-827-4437;
Received: 16 May 2010
Accepted: 21 May 2010
First published online: 14 July 2010
The evolution of problematic plants, both weeds and invasives, is a topic of
increasing interest. Plants that have evolved from domesticated ancestors have
certain advantages for study. Because of their economic importance, domesti-
cated plants are generally well-characterized and readily available for ecogenetic
comparison with their wild descendants. Thus, the evolutionary history of crop
descendants has the potential to be reconstructed in some detail. Furthermore,
growing crop progenitors with their problematic descendants in a common
environment allows for the identification of significant evolutionary differences
that correlate with weediness or invasiveness. We sought well-established exam-
ples of invasives and weeds for which genetic and/or ethnobotanical evidence
has confirmed their evolution from domesticates. We found surprisingly few
cases, only 13. We examine our list for generalizations and then some selected
cases to reveal how plant pests have evolved from domesticates. Despite their
potential utility, crop descendants remain underexploited for evolutionary
study. Promising evolutionary research opportunities for these systems are
abundant and worthy of pursuit.
Evolutionary Applications ISSN 1752-4571
494 ª2010 Blackwell Publishing Ltd 3(2010) 494–504
(including fitness correlates or biotic interactions) of the
invasive or weed and those of putative source populations
(Bossdorf et al. 2005; Dlugosch and Parker 2008a; Keller
et al. 2009). The latter can suggest evolutionary changes,
but ‘common garden’ experiments (e.g., Barrett 1983;
Brodersen et al. 2008; Dlugosch and Parker 2008b) in both
the invaded and the native range are often necessary to dem-
onstrate genetically-based phenotypic or ecological differ-
ences between problematic organisms and their presumed
progenitors (Hierro et al. 2005; Moloney et al. 2009).
Common garden studies have revealed adaptive evolu-
tion in both weeds and invasives. A classical case is that
of a variety of barnyard grass [Echinochloa crus-galli var.
oryzicola (L.) P. Beauv.], a noxious weed that has evolved
to mimic domesticated rice (Oryza sativa L.) (Barrett
1983). Barrett (1983) grew seedlings of E. crus-galli var.
oryzicola, its progenitor, E. crus-galli var. crus-galli, and
O. sativa in a common garden experiment measuring
numerous morphological characters. Multivariate analysis
of 15 quantitative characters revealed that, in their vegeta-
tive phase, rice and its weedy mimic are not significantly
different morphologically from each other, despite being
in different genera. However, both differed significantly
from E. crus-galli var. crus-galli (see Figs 1 and 2 in
Barrett 1983). Morphological crop mimicry is an adapta-
tion that is the result of continued selection by visually-
based human weeding. Indeed, barnyard grass individuals
in Japanese rice fields that most closely resemble culti-
vated rice plants morphologically are less likely to be
removed from rice fields by hand-weeding (Ehara and
Abe 1950). Apparently, thousands of years of hand-weed-
ing rice selected for a crop mimic that is almost vegeta-
tively indistinguishable from rice.
Similar studies have been conducted for invasives. In a
common garden experiment conducted in California,
Dlugosch and Parker (2008b) compared invasive Califor-
nia populations of the shrub Canary Islands St. John’s
wort (Hypericum canariense L.) with the native popula-
tions of that species, including the genetically-determined
precise source population (Tenerife of the Canary
Islands). They found that California populations had
evolved an increased growth rate relative to the source
population. They also found a diversification of flowering
phenology of the California plants that correlated with
their latitudinal origins. Such apparently adaptive evolu-
tionary changes are not uncommon, although some
authors caution that alternative explanations (e.g., climate
matching by populations with multiple geographic ori-
gins) can account equally well for the appearance of
adaptation (Colautti et al. 2009). Only a handful of
experimental studies report no evidence for adaptive
evolution in invasives relative to their putative source
populations (Brodersen et al. 2008).
The example of Dlugosch and Parker (2008b) is excep-
tional for invasives in that the progenitor population was
precisely identified, allowing for the appropriate experi-
mental comparison of progenitor and derived genotypes.
But most often detailed information about source popula-
tions is, at best, lacking or at worst, complicated by an
unknowable number of multiple introductions to multi-
ple locations over decades with little knowledge about the
time and place of initial invasion.
Crops gone wild
A subset of weeds and invasives has evolved from domes-
ticated ancestors, presenting certain advantages for study.
We note that weeds and invasives can evolve from
domesticate plants by two different pathways (Fig. 1).
Some, like California’s weedy rye (Burger et al. 2006) are
directly descended from a crop (endoferal ancestry, sensu
Gressel 2005a), though not all endoferal plant pests neces-
sarily arise via evolutionary change. Other problematic
plants, such as Europe’s weed beet (Mu
¨cher et al. 2000;
van Dijk 2004), are descended from hybrids between a
crop and another, usually wild, taxon (exoferal ancestry,
sensu Gressel 2005a). Knowledge about crop ancestors can
illuminate the evolutionary origins of these problematic
Because of their economic importance, domesticated
plants are often extraordinarily well-studied and well-
characterized; many are among the best studied plants.
Consider this dramatic illustration: Of the hundreds of
thousands of described plant species, roughly 1% are
domesticated, but of the eight completely sequenced plant
genomes, five belong to domesticated plants (NIH Plant
Genomes Website
PLANTS/PlantList.html). Likewise, domesticated species
are attractive for many evolutionary biologists. Charles
Darwin’s The Variation of Animals and Plants under
Domestication (Darwin 1868) was published less than a
decade after his On the Origin of Species by Means of
Natural Selection (Darwin 1859).
Most domesticated species are easily available for experi-
mental and descriptive genetic comparison with their wild
descendants. Thus, the history of crop descendants can
often be reconstructed in some detail. For recently appear-
ing weedy or invasive lineages, historic ethnobotanical
information, confirmed by genetic data, can assign their
geographic origin to a limited region. Similar information
can sometimes be employed to determine which crop sub-
species or varieties might have been involved in the origin
of the troublesome lineage. Furthermore, domesticated
plants are selected to be grown easily. For example, annual
crop seeds typically exhibit no dormancy (Gepts 2004).
This tractability can facilitate common garden experiments
Ellstrand et al. Evolution of weeds and invasives from domesticates
ª2010 Blackwell Publishing Ltd 3(2010) 494–504 495
to identify significant evolutionary changes that correlate
with weediness or invasiveness.
Despite these apparent advantages as well as a recent
major treatment on crop ferality (Gressel 2005b), plants
with domesticated ancestors remain a largely under-
appreciated resource for studying how problem plants
evolve. Our original motivation was to understand how
natural selection works on the descendants of domesti-
cated species so that they are able to become weedy or
invasive. We were hoping to review the literature and
accumulate a large number of examples to determine
sweeping evolutionary generalizations such as whether
natural selection results in, for example, the evolution of
locally adaptation, of increased competitive ability, or of
better dispersal. Below we identify the best studied sys-
tems, those invasive and weedy plants that have been
genetically confirmed as descendants of domesticates. We
found enough examples to identify some potential trends,
but too few to make the broad generalizations that we
had hoped for. Following our general review, we chose a
few examples that provide some insights into the work
that needs to be done on systems such as these. In partic-
ular, in our discussion, we look to the future. We identify
plant pests that are worthy of more evolutionary scrutiny.
We also consider how information from already charac-
terized crop traits might illuminate which and how genes
evolve along the route to pest status. Finally, we discuss a
number of research questions in evolutionary biology that
might be fruitfully pursued in these study systems.
Plant pests descended from domesticates
We sought cases that demonstrate the evolution of inva-
siveness and/or weediness in plants with domesticated
ancestors. We concentrated on finding the most convinc-
ing examples supported by the literature. We used four
criteria for choosing our examples:
1We considered only cases involving ancestors that are
well-domesticated taxa. Here, we define well-domesticated
taxa as those that have been intentionally cultivated (and
thus under intentional or unintentional selection) for at
least 1000 years. This initial filter limits the potential num-
ber of cases to several hundred species (Smartt and Sim-
monds 1995) while eliminating most ornamentals, timber
trees, and forage grasses. Compared to highly-domesti-
cated plants that are well-differentiated from their wild
ancestors, weakly-domesticated taxa are genetically so close
to their wild ancestors that it would be almost impossible
to determine whether their problematic descendants from
have undergone any significant evolutionary change. To
illustrate, Lantana camara is a plant famous in the nursery
trade for escaping cultivation to become a globally signifi-
cant invasive (Sharma et al. 2005). But it is not clear that
the either the horticultural varieties of L. camara or their
invasive descendants are substantially genetically different
from the original wild L. camara populations that are the
original ancestors to both.
We started out search by examining the examples in
Gressel’s (2005b) edited tour de force on crop ferality.
Likewise, Andersson and de Vicente’s (2010) book on
crops and their wild relatives provides detailed informa-
tion on what is known about feral, weedy, and invasive
lineages that have emerged from the world’s most impor-
tant crop species. Some other examples came from prior
treatments that focused on exoferality (e.g., Schierenbeck
and Ellstrand 2009 and references therein).
Crop-to-crop exo-ferality
Crop A
Crop A
Crop B
Crop B
Crop-to-wild exo-ferality
Crop A
Crop A
Crop A
Crop A
No evolution
Figure 1 Pathways from domesticated plant to problem plant. Pest
plants directly descended from domesticated plants (‘endoferal’ sensu
Gressel 2005a) can occur with or without evolutionary change. Plants
that are the result of hybridization between a domesticated taxon and
another taxon (‘exoferal’ sensu Gressel 2005a) are necessarily evolu-
tionarily different than their crop progenitor(s).
Evolution of weeds and invasives from domesticates Ellstrand et al.
496 ª2010 Blackwell Publishing Ltd 3(2010) 494–504
2We required genetic or historical evidence that the
problematic lineage has evolved from a domesticated
taxon. Thus, we excluded from our list plant pests that
are known to have well-domesticated ancestors but for
which no evidence of evolutionary change has yet been
reported (e.g., invasive strawberry guava, Lowe et al.
Likewise, we excluded problematic plants that may be
descended from a crop but could also be descended from
a close wild relative of the crop. Consider the case of wild
sunflowers (Helianthus annuus) that are a substantial
weed and/or invasive problem in their native continent of
North America as well as in parts of Europe (Berville
et al. 2005). While they are the same species as cultivated
sunflower, it has not yet been established whether any of
the H. annuus pest populations are descended from the
crop or if they are simply descended from the North
American wild populations that were the progenitor of
the crop. Interestingly, such research on wild sunflowers
is reported to be underway (Berville
´et al. 2005). But at
the moment, we cannot include such plants in our analy-
Generally, we treated genetic evidence for a history
intertaxon hybridization (exoferality) as ipso facto
evidence that the lineage is genetically different from its
crop progenitor.
3After filtering our list through the first two criteria,
we asked whether evidence existed that the feral lineage is
indeed problematic. For example, many ornamental crops
escape from cultivation and persist (Kowarik 2005), but
only a few become problematic. In most cases, the pri-
mary literature was sufficient to answer the question [e.g.,
de Wet (1995) characterizes weedy finger millet as
‘obnoxious’]. But if the primary literature simply
described a feral lineage as a ‘weed of agriculture’, we
tried to assess its significance elsewhere, such as a major
weed and/or invasive compendium (e.g., Holm et al.
1977, 1997) or official listing as a weed or invasive by a
national or regional authority according to where the
lineage has been reported. For example, Bagavathiannan
et al. (2010) report that feral alfalfa in Canada is
evolutionarily derived from the crop, but a search of
Agriculture and Agri-Food Canada’s website (http:// revealed that that species is not a signifi-
cant pest plant in that country.
4Finally, we required evidence that the lineage is more
problematic than its crop progenitor (in the case of endo-
ferals) or each of its progenitors (in the case of exoferals),
that is, that it actually evolved to become a pest. We
avoid cases in which a wild invasive taxon has picked up
a few crop alleles via hybridization on its invasive spree
without a relevant evolutionary change to increased inva-
We found 13 examples of plant pest lineages are des-
cended from crop progenitors. These are enumerated in
Table 1. Ten are primarily noxious weeds of agriculture,
one is an invader of nonmanaged ecosystems, and the
remaining two are both weedy and invasive. Six have an
endoferal ancestry; six are descended from hybrids
between a domesticated taxon and a wild relative. In the
remaining case, the plant pest lineage is descended from
hybrids between two cultivated taxa.
Two of the studies contributing to our list found both
a crop origin and a noncrop origin for what has been
considered to be a single taxon; that is, some, but not all,
of the populations studied had crop ancestors. With
regards to weedy rice in the United States, Londo and
Schaal (2007) found that most of the accessions geneti-
cally analyzed and compared with an array of putative
ancestors were either descended from hybrids (mostly
‘strawhull’ weedy rice) or from the crop (mostly ‘black-
hull’ weedy rice). But a single accession from California
appeared to be descended directly from the wild ancestor
O. rufipogon. In the similar study of wild artichoke thistle
(Cynara cardunculus L.) in California (Leak-Garcia 2009),
of the 12 wild populations analyzed, four were found to
have domesticated ancestry and eight were found to be
descendants of Old World wild artichoke thistle.
The list in Table 1 is diverse. The plants are annuals
and perennials whose seed and pollen are dispersed in a
variety of ways. Cultivated progenitors include both agro-
nomic and horticultural crops. Given the importance of
the grass family for human sustenance, it is not surprising
that most of the examples are from that family.
A few generalizations are apparent. With the exceptions
of rice and wheat with endoferal ancestry, all other cases
involve at least one parent that is predominantly
outcrossing; in most of the cases at least one parent is
self-incompatible. It is certainly possible that outcrossing
could facilitate the recombination of genetic diversity
between previously isolated lines, creating a burst of vari-
ation that can generate an array of phenotypes for a selec-
tive substrate (Ellstrand and Schierenbeck 2000;
Schierenbeck and Ellstrand 2009). Whether this general-
ization will hold up as more systems are studied remains
to be seen.
Also, many of the reported evolutionary changes repre-
sent de-domestication, the evolutionary loss of traits
accumulated under domestication (Gressel 2005a). Nine
of our examples show an evolutionary shift to readily dis-
persed seeds or fruits. Typically, agronomic crops that are
grown for their seeds have evolved under human selection
to be ‘nonshattering;’ that is, the infructescence or fruit
holds seeds on the plant until harvest (Gepts 2004). The
wild ancestors of those crops have the ‘shattering’ trait
for dispersal. So, too, do more than half of our examples,
Ellstrand et al. Evolution of weeds and invasives from domesticates
ª2010 Blackwell Publishing Ltd 3(2010) 494–504 497
Table 1. Invasives (I) or weeds (W) determined to have evolved from domesticated plants.
Common name
of plant pest
Type of ferality
Source location of
crop descendant
Key evolved traits
relative to crop ancestor Habit Citations
I Artichoke
thistle (in part)
Artichoke (Cynara cardunculus var. scolymus)*
California, USA Development of spininess, smaller more
numerous heads, leaves deeply dissected,
delayed and extended flowering period
Perennial herb Leak-Garcia (2009)
W Semi-wild
Bread wheat (Triticum aestivum)*
Tibet, China Easily broken rachis which facilitates
Annual grass Sun et al. (1998);
Ayal and Levy (2005)
W Weedy finger
Finger millet (Eleusine coracana subsp.
coracana)* ·wild finger millet
(Eleusine coracana subsp. africana)
Africa Disarticulating spikelets Annual grass Hilu et al. (1978);.
de Wet et al. (1984);
de Wet (1995)
W Johnsongrass Grain sorghum (Sorghum bicolor)* ·Johnsongrass
(S. halepense)
Nebraska and
Texas, USA
Perennial, shattering, rhizomatous Perennial grass Morrell et al. (2005)
W Columbus
Grain sorghum (Sorghum bicolor)* ·
S. propinquum
‘Diverse geographic
Perennial, shattering, rhizomatous Perennial grass Paterson et al. (1995)
W Forrageiro Radish (Raphanus sativus)*
Rio Grande do
Sul, Brazil
Resistance to ALS-inhibiting herbicides Annual or
biennial forb
Snow and
Campbell (2005)
I/W California wild
Radish (Raphanus sativus)* ·Jointed
charlock (R. raphanistrum)
California, USA Earlier bolting, earlier flowering,
increased flower number,
unexpanded hypocotyl, increased
fruit number, increased seed number
Annual or
biennial forb
Hegde et al. (2006)
Ridley et al. (2008);
Ridley and
Ellstrand (2009)
W Weedy rice Rice (Oryza sativa japonica)*
Liaoning, China Shattering Annual grass Cao et al. (2006)
W ‘Blackhull’
weedy rice
Rice (Oryza sativa indica)*
Southeastern USA Seed dormancy, shattering Annual grass Londo and Schaal
W Weedy rice Rice (Oryza sativa japonica)* ·Rice (O. s. indica)*
Exo-endoferal (feral lineage descended from
hybrids between two crops)
Bhutan Seed dormancy, shattering Annual grass Ishikawa et al. (2005)
W ‘Strawhull’
weedy rice
Rice (Oryza sativa indica)* ·Brownbeard rice
(O. rufipogon)
Southeastern USA Seed dormancy, shattering Annual grass Londo and Schaal
I/W Weedy rye,
feral rye
Rye (Secale cereale)*
California and
Washington, USA
Shattering, smaller seed,
delayed flowering
Annual grass Suneson et al. (1969);
Burger et al.
(2006, 2007)
W Weed beet Sugarbeet (Beta vulgaris subsp. vulgaris)* ·
Sea beet (B. v. maritima)
France, Germany, Italy Shift to annual from
biennial habit, woody root
Annual forb Mu¨ cher et al. (2000);
van Dijk (2004)
*Domesticated plant.
Evolution of weeds and invasives from domesticates Ellstrand et al.
498 ª2010 Blackwell Publishing Ltd 3(2010) 494–504
indicating the evolutionary reversal of this trait in the
successful derived populations. Three of our examples
display the evolution of increased seed dormancy relative
to their crop ancestors. Some dormancy in the wild is the
rule for monocarpic plants; it has long been interpreted
as an evolutionary ‘bet-hedging’ strategy by plant evolu-
tionary ecologists (Venable 2007). As noted above,
domesticated annual crops typically have no dormancy,
an anthropogenic adaptation that permits quick and uni-
form germination when sown (Gepts 2004).
In at least one case, the key evolutionary change from
a domesticated plant to a pest did not involve the evolu-
tionary reversal of de-domestication. Cultivated radish
(Raphanus sativus L.) in southern Brazil has evolved resis-
tance to ALS-inhibiting herbicides, the herbicides of
choice in that region for no-till agriculture (Snow and
Campbell 2005). The resulting lineage called ‘forrageiro’,
is now a weed of both winter and summer crops. That
trait is not present either in the crop or in its progenitors;
thus, its evolution is not a case of de-domestication.
In contrast with the examples of divergence from
domesticated ancestors discussed above, in some of our
cases certain domesticated traits are retained in the feral
lineages. Those traits have not evolved because they pre-
sumably provide an evolutionary advantage. In particular,
several of the cases in Table 1 are successful because they
retained traits making them functional crop mimics.
Weedy rice, weedy beet, weedy rye, and semi-wild wheat
are hard to control because until they flower, they are
morphologically hard to distinguish from their relatives.
Thus, their survival is enhanced under hand-weeding.
One of the two most significant generalizations is that
the list is short. As we worked our way through the 25
contributed chapters of Crop Ferality and Volunteerism
(Gressel 2005b), we were surprised that many of the
treatments of feral plants offered only agronomic and
ecological detail, but very little insight into whether they
had evolved from their cultivated ancestors. We contend
that the other significant generalization is that there is
much to learn from these systems. With few exceptions,
our list is simply a recounting of studies that combine
data from genetic markers with ethnobotanical history to
establish that problem plants evolved from domesticates.
Even data regarding the traits that make these plants
problematic are largely superficial.
However, we found three systems worthy of deeper dis-
cussion. First, we highlight the evolution of weedy rice
because it illustrates how what is often perceived as a sin-
gle problematic lineage is, in fact, a polyphyletic set of
lineages with a diversity of evolutionary pathways that
capture the breadth of how plant pests evolve from crop
ancestors. In contrast the monophyletic story of endoferal
weedy rye has been shown to have undergone both rapid
evolutionary divergence from its progenitor as well as
regional evolutionary diversification in considerably less
than a century. We conclude with the curious case of
California wild radish, an exoferal derivative of two
species that spontaneously hybridize throughout the
world; interestingly, that hybridization has yielded a prob-
lematic lineage in only one region.
Three examples of the evolution of problematic
plants from domesticated ancestors
Weedy rice in China, the United States, and Bhutan
Native to Asia, cultivated rice (Oryza sativa japonica and
O. sativa indica) is the world’s most important food crop.
Weedy rice (O. sativa f. spontanea), also known as ‘red
rice’, has been an important weed of cultivated rice
worldwide for hundreds of years (Holm et al. 1997). Veg-
etatively, weedy rice is a crop mimic (Valverde 2005), but
its infructescence shatters, and its seeds typically exhibit
some dormancy. When it co-occurs with rice, the crop
suffers depressed yields, and, when co-harvested, the seeds
of the weed degrade the quality of the harvested grain.
Because it is the same species as cultivated rice, with
similar morphology and physiology, it is very difficult to
control by both weeding and chemical means.
The evolutionary origin of weedy rice has been contro-
versial. Its putative ancestry includes various hypotheses:
that is a wild relative of rice that has evolved crop mim-
icry, that it is descended directly from cultivated rice, or
that it is an exoferal lineage descended from hybrids
between a wild taxon and cultivated rice (Vaughan et al.
Three recent genetic studies of weedy rice have
addressed its evolutionary origins. After decades of suc-
cessful suppression, in the last decade weedy rice has
emerged as a problem in the rice fields of certain regions
of China (Cao et al. 2006). Motivated by the resurgence of
this pest, Cao et al. (2006) compared 20 DNA based SSR
markers from 30 populations of weedy rice collected from
China’s Liaoning province with those of wild O. rufipogon
as well as selected rice varieties from the two major culti-
var groups, japonica and indica. Statistical analysis of the
genetic data revealed the local Liaoning cultivar (a
japonica type) clustered within the array of weedy rice
populations. Another major Chinese japonica cultivar
showed much less affinity. The wild O. rufipogon and
domesticated indica types were even more distantly related
from the Liaoning weeds. The authors conclude ‘weedy
rice populations from Liaoning most probably originated
from Liaoning rice varieties by mutation and intervarietal
hybrids’. We agree that an intertaxon hybrid origin for
Liaoning weedy populations is unlikely; if hybridization
had occurred, it is likely that some O. rufipogon alleles
Ellstrand et al. Evolution of weeds and invasives from domesticates
ª2010 Blackwell Publishing Ltd 3(2010) 494–504 499
would have been retained in the weedy lineages in the
short time that they have been problematic.
Weedy rice has been a problematic weed of rice in the
southeastern United States for well over a century (Gealy
2005). To identify the origins of this weed Londo and
Schaal (2007) took a similar approach to Cao et al. (2006),
genetically analyzing 29 different United States weedy rice
accessions from six different states to ‘cover the entire
range of US rice culture’. For comparison, they chose 113
accessions representing a variety of indica and japonica cul-
tivars, O. rufipogon, and other wild relatives. They used data
from both sequencing a nuclear pseudo-gene (p-VATP)
and 21 DNA-based microsatellite loci. The authors used
the program STRUCTURE (Pritchard et al. 2000) to infer
the origin of the weedy rice accessions and their possible
history of hybridization. STRUCTURE uses a Bayesian
approach to examine the relationships of multilocus geno-
types of individuals by differences in allele frequency and
the nature of linkage disequilibrium. In the United States,
the vast majority of cultivars are japonica types, but
STRUCTURE analysis assigned almost all of the US weedy
accessions to two groups unallied with japonica. Black-
hulled weedy rice and a few other accessions were almost
identical to domesticated O. sativa indica var. Aus; straw-
hulled weedy rice and a few other accessions were classified
with exoferal ancestry involving hybridization of O. sativa
indica and wild O. rufipogon. A single accession appeared to
be descended directly from the wild ancestor O. rufipogon.
Clearly, most of the US weedy rice populations evolved
from the cultivated species, but it is also clear that evolu-
tion did not occur in the United States. These data as well
as other historical data (Gealy 2005) suggest that US weedy
rice has an Asian origin.
Yet another pathway for the origin of weedy rice has
been described for its populations in Bhutan (Ishikawa
et al. 2005). In that country japonica rice cultivars pre-
dominate in the highlands while indica cultivars predomi-
nate in the lowlands. Ishikawa et al. (2005) compared
lowland cultivars, highland cultivars, and weedy popula-
tions with regards to nine isozyme loci, a chloroplast gen-
ome deletion, and four microsatellite loci. They found
clear genetic differentiation between japonica and indica
cultivars, and at the same time, they found that the weedy
populations had genotypes that had both combinations of
both japonica-specific alleles and indica-specific alleles.
They report that they did not detect any alleles specific to
wild relatives. Thus, their conclusion is that the weedy
populations are lineages descended from japonica x indica
hybrids. When Gressel (2005a) named the different evolu-
tionary pathways to ferality, he did not consider intercul-
tivar hybridization. Following his lead, we call this
particular pathway for Bhutanese weedy ricde ‘exo-endof-
erality’ because it is first a case of endoferality because all
ancestors are domesticates, but also ‘exo-’ because inter-
taxon hybridization is a critical evolutionary step.
All three of the above comprehensive studies present
strong evidence for the origin of the vast majority of the
weedy rice populations to be from cultivated rice. Inter-
estingly, the data collected reveals a polyphyletic origin
for weedy rice. Polyphylesis is now well-known to play a
role in the evolution of many invasive lineages (Novak
2007) but it is not clear whether it is the rule for domes-
ticate-derived pests.
For three of the four discovered pathways, involving
direct ancestry from indica and japonica, de-domestica-
tion likely occurred via the evolution of (at least) shatter-
ing due to either mutation or an epistatic recombination
event. The most parsimonious pathway for the remaining
exoferal lineage detected by Londo and Schaal (2007) is
for O. rufipogon to have provided the allele or alleles for
Weedy rye in western North America
In terms of area planted, cereal rye (Secale cereale L.) is
one of the world’s top 10 grain crops. Volunteer rye has
occasionally been a serious agricultural weed problem
throughout North America for about 100 years. However,
by the early 1960s self-sustaining, naturalized weedy rye
populations were identified as increasingly problematic as
weeds of cultivated lands and invasives of uncultivated
lands in the US states of Washington, Oregon, Idaho, and
California. As a weed of cultivated rye, it was so bad that
‘farmers abandoned efforts to grow cultivated rye for
human consumption’ (National Research Council 1989).
Subsequently, weedy rye has spread elsewhere in the wes-
tern United States and the Canadian province of British
Columbia (Burger and Ellstrand 2005).
Western North American weedy rye was originally
thought to be a hybrid derivative of cultivated rye and
the wild perennial mountain rye [S. strictum (C. Presl) C.
Presl.]. However, subsequent genetic analysis of several
populations of North American weedy rye with 14 allo-
zyme and three microsatellite loci failed to detect any
ancestry from S. strictum or any other wild Secale. Over-
all, the weedy populations are more similar to each other
than to any one cultivar. Nonetheless, the invasive popu-
lations share a single lineage that apparently evolved
directly from one or more cultivars of cereal rye (Burger
et al. 2006).
Just as in the case of rice, cultivated rye is nonshatter-
ing and has little dormancy, while its derivative has
evolved dispersal by shattering. De-domestication of the
nonshattering trait to shattering likely occurred via muta-
tion or perhaps an epistatic recombination event. Inter-
estingly, in this case, both the crop and the feral
Evolution of weeds and invasives from domesticates Ellstrand et al.
500 ª2010 Blackwell Publishing Ltd 3(2010) 494–504
populations have little seed dormancy. Other traits such
as smaller seed, smaller leaves, thinner culms, and delayed
flowering have rapidly evolved in this lineage (roughly 60
generations since original observations of volunteer popu-
lations) (Burger et al. 2007). It is not clear whether all of
these traits contribute to its evolution as a plant pest,
especially its invasiveness outside of agroecosystems.
However, evolution of a change in flowering time relative
to an ancestor can be a powerful reproductive isolating
mechanism. In this case, it might have evolved under
selection to frustrate maladaptive gene flow (‘reinforce-
ment’ of isolation) from the crop to the weedy lineage
(Levin 1978; see our relevant expanded discussion of evo-
lution of reproductive isolation below).
Wild radish in far western North America
Cultivated radish (R. sativus) is an important vegetable
whose root (botanically, the expanded hypocotyl) is con-
sumed worldwide. The wild jointed charlock (R. raphani-
strum L.; sometimes, confusingly called ‘wild radish’) is a
closely related species, separated from the cultigen by a
chromosomal translocation and a suite of morphological
characters. When the two co-occur in most of the world,
spontaneously hybridization occurs to a limited extent,
resulting in no more than highly localized hybrid swarms
(Snow and Campbell 2005).
In contrast, for almost 100 years, hybridization between
the two Raphanus taxa in California has been more exten-
sive (Frost 1923; Panetsos and Baker 1967). In the last
50 years, hybrid-derived wild Raphanus has invaded
coastal plains and disturbed inland valleys along the Paci-
fic edge of North America from the US state of Oregon
south through California to the Mexican state of Baja
California (Whitson 2006). It has also become a trouble-
some weed for agronomic crops.
Experimental work on what is now known as ‘Califor-
nia wild radish’ has confirmed it to be a lineage des-
cended from hybrids of R. sativus and R. raphanistrum.
Hegde et al. (2006) compared California wild radish
populations with cultivars of R. sativus and populations
of R. raphanistrum. They used 10 allozyme loci as well as
common garden experiments to characterize the three
types. The allozyme data revealed that California wild
radish populations were in Hardy-Weinberg equilibrium;
that is, there was no evidence that pure individuals of the
parental taxa had persisted in significant frequencies.
STRUCTURE analysis of the allozyme dataset confirmed
that conclusion. STRUCTURE assigned the cultivated
radish to one group and the jointed charlock individuals
to another group. The individuals from the California
wild radish populations were assigned at various levels of
hybrid ancestry involving the first two groups. Multivari-
ate analysis of morphological characters measured in their
common garden experiments revealed that the standard
phenotype of California wild radish is significantly differ-
ent from both of its progenitors. Interestingly, its bolting
date, flowering date, and hypocotyl width are intermedi-
ate to its progenitors; its fruit diameter and fruit length
are the same as the cultigen; and its fruit weight trans-
gresses both parents! A subsequent common garden
experiment showed that in several, contrasting California
environments, the hybrid lineage produced both more
fruits per plant and more seeds per plant than either pro-
genitor (Ridley and Ellstrand 2009), including specific
source cultivars and R. raphanistrum populations as
determined from cpDNA analysis (Ridley et al. 2008).
Is there something special about California that permit-
ted this rapid adaptive evolution to proceed in light of
the fact that Raphanus hybrids elsewhere have proven to
be evolutionary deadends? Another common garden
experiment has given a tantalizing result. Synthetic, F
generation hybrid lineages and their R. raphanistrum pro-
genitors were grown in the field in Michigan and Califor-
nia. The hybrid lineages’ fitness was slightly inferior to
R. raphanistrum in Michigan but in California they exhib-
ited 22% greater survival and 270% greater lifetime
fecundity (Campbell et al. 2006; see also Campbell and
Snow 2009).
Avenues for future research
Evolutionary studies on weedy and/or invasive plants that
have domesticated ancestors have been useful for detailing
the phylogenetic history of such plants. More examples
might exist. While accumulating our examples for
Table 1, we encountered some cases for which the current
evidence is too weak at this time to convincingly support
or refute a crop origin for an invasive lineage. These are
enumerated in Table 2. Likewise, we encountered exam-
ples of domesticated taxa that have become plant pests,
but it is not clear whether these have evolved to become
pests or are simply ecological opportunists (Table 3).
Consider the case of strawberry guava (Psidium cattleia-
num Sabine). The free-living version of this domesticated
plant is considered by some to be one of the world’s
worst invasive species (Lowe et al. 2000), but no studies
have examined whether the invasive strawberry guava
populations are substantially genetically different from
their domesticated progenitor.
The majority of our entries in Table 1 are examples of
remarkably rapid evolution, at least six of our problem-
atic lineages evolved in less than a century. The compari-
son of progenitors and their wild descendants grown in a
common environment reveals differences that may
account for the success of the latter.
Ellstrand et al. Evolution of weeds and invasives from domesticates
ª2010 Blackwell Publishing Ltd 3(2010) 494–504 501
Nonetheless, research on such systems has barely
exploited their utility for evolutionary study in compari-
son with certain other plant pests, such as the large
body of integrated ecological, physiological and genetic
study employed to understand evolution of invasiveness
in North American reed canarygrass (Phalaris arundina-
cea L.) by Molofsky and colleagues (Lavergne and Mol-
ofsky 2004) (For some other examples of rapid
evolution in invasive plant species see Xu et al. (2010)
and references therein). In particular, invasives and
weeds descended from domesticated plants are ripe for
approaches to tease out the evolutionary pathway to
their new lifestyle. How do they differ from their pro-
genitors with respect to their ecological relationships
with biotic enemies, that is, herbivores and disease-caus-
ing organisms? Are there any differences in their chemi-
cal or physical defenses?
Genetic and genomic approaches, often used in concert
with ethnobotanical data, have been successful in illumi-
nating the evolution of crops from wild species under
domestication (Purugganan and Fuller 2009). These
approaches may prove to be equally powerful in investi-
gating evolution in the other direction, the evolution of
sustainable feral populations from domesticated species.
Let’s consider some of these approaches.
Refined cytogenetic tools for studying chromosomal
evolution under domestication have expanded to include
not only traditional chromosome banding, but also tech-
niques using fluorescent in situ hybridization (FISH)
(e.g., Zhang et al. 2002) and genomic in situ hybridization
(GISH) (e.g., Stace and Bailey 1999). Despite the fact that
many major crops are cytogenetically well-characterized,
we are not aware of any studies that address whether
and how chromosomal evolution has occurred under
Even if a crop species hasn’t had its genome sequenced,
it is likely to be well-mapped. Quantitative trait locus
(QTL) mapping has proven a powerful way to study the
domestication-related genes (Paterson 2002) by examining
the co-segregation of a trait with markers to determining
the number of loci, their chromosomal location, and their
relative influence on the expression of that trait. For
example, the first maize ‘domestication gene’, teosinte
branched1 (tb1), was identified by QTL mapping (Doeb-
ley et al. 1995). In the same way, crosses between plant
pests and their crop progenitors can be made to examine
the genetic basis of key ecological traits that correlate with
invasive success (Prentis et al. 2008).
Evolutionary genomic approaches have proven particu-
larly fruitful for identifying the genomic and genetic cor-
relates of crop domestication, in particular, potential
adaptive changes (e.g., Ross-Ibarra et al. 2007). For
domesticated taxa that have had their genome sequenced,
such as rice and sorghum, comparative evolutionary eco-
genomic approaches with their descendants will be able
to provide a sweeping view of what genomic changes have
occurred in the evolution of invasives and/or weeds rela-
tive to their crop ancestor. As genome sequencing become
both less expensive and easier to conduct (http://, such approaches will become
available for more species, but the descendants of domes-
ticated taxa will still have the advantage of centuries of
We end with a few intriguing questions based on the
simple observation that crops and weeds often have a lot
in common ecologically. First, with regard to crops and
their weedy derivatives, we note that both grow in exactly
the same location, but they are subjected to different selec-
tion regimes. How do weedy crop derivatives end up per-
ceiving different selection pressures so that diverge in
sympatry? Furthermore, how do they diverge given that
they are likely to be swamped by gene flow from the
initially more abundant crop? With regards to the latter
Table 2. Invasives (I) or weeds (W) with too little evidence to determine whether they are descended from domesticated plants.
Common name of
plant pest Possible crop progenitor (s) Citations
I Fennel Fennel, Foeniculum vulgare Bell et al. (2008)
I Sunflower Cultivated sunflower, Helianthus annuus Berville
´et al. (2005)
I Jerusalem artichoke Jerusalem artichoke, Helianthus tuberosus* Berville
´et al. (2005); Kowarik (2005)
W Green bristlegrass Foxtail millet, Setaria italica Darmency (2005)
W Shattercane Grain sorghum, Sorghum bicolor Ejeta and Grenier (2005)
Table 3. Invasives (I) or weeds (W) that are descended from domesti-
cated plants but whether they have evolved is not known.
Name of plant pest and its progenitor Citations
I Strawberry guava (Psidium cattleianum) Lowe et al. (2000)
I,W Callery pear (Pyrus calleryana) Culley and
Hardiman (2009)
I Arabica coffee (Coffea arabica) Joshi et al. (2009)
I Robusta coffee (Coffea canephora) Joshi et al. (2009)
Evolution of weeds and invasives from domesticates Ellstrand et al.
502 ª2010 Blackwell Publishing Ltd 3(2010) 494–504
question, it is clear that reproductive isolating barriers
must evolve rapidly, perhaps explaining why our list of
examples is short (that is, evolution of sustainable feral
populations is difficult). And, at the same time, that would
explain why phenological divergence has been noted for all
of our examples descended from an outcrossing crop
ancestor (artichoke, radish, rye, beet) which would be sub-
ject to a rain of cross-compatible pollen, but not for all of
those descended from a highly selfing crop ancestor
(wheat, finger millet, sorghum, rice) for which relatively
short distances should afford reproductive isolation.
Second, both crops and weeds are often selected for a
life in a disturbed habitat. Both characteristically grow
densely in simple communities or even monocultures. If
humans select crops that grow densely in monospecific
stands, are those plants only a few allele changes away
from becoming invasives or weeds (de Wet and Harlan
1975)? If such is the case, careful and thorough evaluation
should accompany the development of new crops designed
to answer pressing societal needs, including new bioenergy
feedstocks created with the goal of providing a stable
domestic energy supply (Barney and DiTomaso 2008).
Our initial manuscript benefited from the ideas of Profes-
sor Jeffrey Ross-Ibarra and his Graduate Genetics Group
at the University of California at Davis. The authors
thank Bao Doan, Baorong Lu, Jeffrey Ross-Ibarra, Allison
Snow, and two anonymous reviewers for their ideas and/
or insightful contributions to subsequent versions of this
manuscript. This work was supported by NSF DEB-
0409984 and NRI-CSREES-USDA 2003-35320 grants to
N.C.E. as well as a US Environmental Protection Agency
(EPA) Science to Achieve Results (STAR) Graduate Fel-
lowship to C.E.R. EPA has not officially endorsed this
publication, and the views expressed herein might not
reflect the views of EPA.
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... Nevertheless, their inclusion as part of the DWWC has not yet been recognized. The latter thus presents an unusual opportunity as it represents the early portion of the evolutionary trajectory to de-domestication (Ellstrand et al., 2010). The sixth category is one of the world's worst rice weeds, weedy rice (Oryza spp.). ...
... The large cluster (Cluster III) reflects the close genetic relationship among inbred cultivars, landraces, feral and weedy types. The feral populations were grouped with inbred rice varieties as they are currently undergoing the process of de-domestication (Ellstrand et al., 2010). A considerable number of feral individuals were grouped with the wildO. ...
... than vice versa (M=4.334), and significant gene flow was observed from cultivated rice to feral rice (M=8.1597) (Table 1), implying an early stage of de-domestication (Ellstrand et al., 2010). Pollen-mediated gene exchange occurs between crops and weeds or wild relatives and between weedy and wild relatives. ...
Genetic studies of Domesticated-Weed-Wild Complexes (DWWC) have typically focused on one-way introgression of crop alleles into wild or weedy populations, with little consideration of the entire natural ecosystem. In Sri Lanka, DWWC is diverse, comprising six evolutionarily discrete groups in the genus Oryza. Using 33 neutral simple sequence repeat (SSR) loci, we characterized six Oryza groups to understand the genetic background and evolution of DWWC components. Our analysis found that Oryza groups have large population sizes and high inter-group long-term gene flows. Asymmetric gene flows were found between wild and weedy rice groups, but the rare alleles shared among DWWC components provide additional evidence for extensive and enduring exchange, highlighting the dynamic nature of this complex genetic admixture among different Oryza lineages. We found high genetic diversity at the population and species levels due to mixed DWWC components over the generations. Weedy rice types exhibit genetic incorporation through admixture from both crop and wild species, highlighting the multi-way genetic transfer in the evolution of weedy rice types. Our findings support the idea that the DWWC is an integrated complex in the Sri Lankan rice ecosystem and that its weedy rice has multiple origins, including de-domestication via feralization of cultivated rice, inter-varietal hybridization among distinct cultivated rice types, adaptation, and invasion of rice cultivation areas by wild Oryza species, and hybridization events between crop and wild rice populations. Abandoned rice domesticates can also evolve into weedy forms with less intimate human relationships and contaminate the rice ecosystem.
... There are three possible routes of weed evolution: from standing variation of wild species, from hybrids between wild and crop taxa (exoferality), and from direct de-domestication of crop cultivars (endoferality). [1][2][3][4] In addition, weeds can be classified according to their habitats: agrestal or agricultural weeds, understood as plants that colonize and thrive in the disturbances created by farming (inside crop fields); or ruderal weeds, understood as plants growing on roadsides, waste piles, and other non-agricultural disturbances. In this review, we focus on agricultural weeds (hereafter simply referred to as "weeds") derived from hybridization with crops (exoferality) and de-domesticated crops (endoferality). ...
... We searched for documented examples of the evolution of feral agricultural weeds from domesticated taxa. In our literature search, we took account of experimental and review articles following the procedure described by Ellstrand et al. 3 with some modifications. Briefly, we first sought cases involving relatives of well-domesticated taxa. ...
... Unlike well-domesticated crops that are highly differentiated from their wild ancestors, incompletely or weakly domesticated crops are genetically so close to their wild ancestors that it would be difficult or almost impossible to determine whether their weed descendants have experienced any significant evolutionary change. 3 However, we included Brassica napus (oilseed rape), although it has been intentionally cultivated for less than 1000 years, owing to its global importance. 102 Second, we regarded cases with historical or genetic evidence that the problematic lineage was derived from crop-wild hybridization (exoferal lineage) or de-domesticated crops (endoferal lineage). ...
Agricultural weeds descended from domesticated ancestors, directly from crops (endoferality) and/or from crop-wild hybridization (exoferality), may have evolutionary advantages by rapidly acquiring traits pre-adapted to agricultural habitats. Understanding the role of crops on the origin and evolution of agricultural weeds is essential to develop more effective weed management programs, minimize crop losses due to weeds, and to accurately assess risks of cultivated genes escaping. In this review, we first describe relevant traits of weediness: shattering, seed dormancy, branching, early flowering and rapid growth, and their role in the feralization process and, furthermore, we discuss how the design of ‘super-crops’ can affect weed evolution. Then, we searched for literature documenting cases of agricultural weeds descended from well-domesticated crops, and describe six case studies of feral weeds evolved from major crops: maize, radish, rapeseed, rice, sorghum, and sunflower. Further studies on the origin and evolution of feral weeds can improve our understanding of the physiological and genetic mechanisms underpinning the adaptation to agricultural habitats and may help to develop more effective weed control practices and breeding better crops.
... 3 Very rarely, it was observed that the domesticated crop plants sporadically obtaining again (recapture) some of the habitat similar to wild-like traits at the time of natural evolution. 4 This type of evolutionary event is considered as de-domestication phenomenon. This type of phenomenon is also termed as feralization and detected in both the animal and plant kingdoms specifically in livestock species and crop plants, for example found in wheat and rice. ...
... Adaptability in the natural feral and harsh environmental conditions of the dedomesticated crop varieties remains unclear. 4 Newly arisen additional novel mutations may play vital role in environmental adaptation during de-domestication. Wild rice gene(s) may play important role by contributing new mutation/variations which are introgressed into the domesticated crop varieties during the time of domestication and may play important roles for sustainable adaptation to the harsh environmental conditions during dedomestication event through balancing selection. ...
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Weedy rice (Oryza sativa f. spontanea) is considered a feral crop wild relative (CWR) of cultivated rice (O. sativa) and has become common weeds of rice fields globally. Weedy rice has been generated either through hybridization or gene flow process between wild rice O. rufipogon and cultivated rice during domestication event. Weedy rice is a conspecific to cultivated rice under the family poaceae which are annual and self-pollinating plant. Weedy rice retains a wide range of diversity in the phenotypic features for adaptation in natural harsh climatic conditions. Many biotic and abiotic stresses tolerance traits have been accumulated slowly through natural evolution to withstand climatic fluctuation. Agromorphological traits were assessed in weedy rice including wild rice and cultivated rice following DUS test protocol for proper characterization and comparative studies. Physicochemical properties such as ASV, GT, GC and sensory based aroma were carried out for six rice genotypes. Phenol test conducted to categories the rice genotypes. Caryopsis ultrastructure was studied using SEM for more clarity in grain fine structural anatomy. Plant height in weedy rice is on average 94.40 cm, and in wild rice it is 120.19 cm. Flag leaf length is 33.69 cm in weedy rice, in case of wild rice it is 21.21cm. Thousand grain weight is 22.50 g in weedy rice whereas in wild rice it is only 13.50 g. Grain per panicle is high in weedy rice (117.10 grain/panicle) but very less in wild rice (39.80 grain/panicle). Weedy rice showed phenol positive reactivity due to presence of PPO (enzyme). Sadanunia was negative in phenol test, is a local aromatic variety. Starch granules mainly CSG ranges from 5.88 to 13.33 μm with irregular spherical structure in weedy rice. In wild rice, CSG is polyhedral structure without any angularity (5.45 μm to 16.26 μm in size). CSG are various shape and size, spherical to polyhedral with moderate angularity (3.53 to 13.748 μm in size) in Banni. PB is moderately present with less impression of PB (0.692 to 1.53 μm in diameter) in all the rice genotypes. It was detected that CSG ranges from polyhedral to spherical in shape and size from 3.53 to 23.07 μm. Both wild rice (O. rufipogon) and weedy rice (O. sativa f. spontanea) have long awn with barbed features (329.169 to 358.489 μm). Main aim of the present work is to explore the reservoir of natural variations in weedy rice based on agro-morphological characteristics and ultra-structure of the caryopsis under SEM and to utilize feral rice for the crop improvement program in near future. Therefore, it needs conservation through on farm in situ process and utilization in the breeding program to develop climate resilient high yielding improved rice varieties with quality grain for sustainable food security. This precious genetic resource of Oryza species is to be utilized in future breeding program to introgress the naturally occurring stress tolerance genes for both biotic and abiotic tolerance potentiality to develop climate ready rice varieties.
... Raphanus sativus is not known in the wild (Warwick, 2011); however, spontaneous populations of radish have been found as a weed infesting crops in several parts of the world, including North America, South America, and South Africa (Hegde et al., 2006;Barnaud et al., 2013;Vercellino et al., 2018;Costa et al., 2021;Heap, 2023). In North America, its invasive capacity is attributed to introgression with a closely related species, R. raphanistrum (known as California wild radish) (Hegde et al., 2006;Ellstrand et al., 2010), and in South America, it can be found in Argentina, Brazil, Chile, Uruguay, and Paraguay (Pandolfo et al., 2018a). In Argentina, weedy radish is present in 20 of 23 provinces and has been considered a widespread invasive weed since at least the 1930s (Ibarra, 1937;Pandolfo et al., 2018a). ...
... Since this practice could only be carried out in farmer fields, but not in seed production areas where the risk of dispersion is considerably higher (e.g., weedy beet in Europe; Bartsch 2010), we propose that the introduction of cultivated radish in areas with weedy radish should be carried out with extreme care, i.e., by planting cultivated radish in weedy radish-free plots and by controlling weedy radish plants in its surroundings. Considering that weed evolution after the introduction of a new crop in a new area has been demonstrated in several crop-weed complexes, with multiple negative impacts (reviewed by Ellstrand et al., 2010;Vercellino et al., 2023), we recommend a thorough agroecological and environmental risk assessment of the introduction of a new crop (e.g., radish cover crop) before it is approved for production and commercialization. In addition, integrated weed management strategies aimed at preventing gene flow with the crop should be a priority to prevent the emergence and spread of novel more problematic weedy radish biotypes (reviewed by Vercellino et al., 2023). ...
Premise: The phenotype of hybrids between a crop and its wild or weed counterpart is usually intermediate and maladapted compared to that of their parents; however, hybridization has sometimes been associated with increased fitness, potentially leading to enhanced weediness and invasiveness. Since the ecological context and maternal genetic effects may affect hybrid fitness, they could influence the evolutionary outcomes of hybridization. Here, we evaluated the performance of first-generation crop-weed hybrids of Raphanus sativus and their parents in two contrasting ecological conditions. Methods: Using experimental hybridization and outdoor common garden experiments, we assessed differences in time to flowering, survival to maturity, plant biomass, and reproductive components between bidirectional crop-weed hybrids and their parents in agrestal (wheat cultivation, fertilization, weeding) and ruderal (human-disturbed, uncultivated area) conditions over 2 years. Results: Crop, weeds, and bidirectional hybrids overlapped at least partially during the flowering period, indicating a high probability of gene flow. Hybrids survived to maturity at rates at least as successful as their parents and had higher plant biomass and fecundity, which resulted in higher fitness compared to their parents in both environments, without any differences associated with the direction of the hybridization. Conclusions: Intraspecific crop-weed hybridization, regardless of the cross direction, has the potential to promote weediness in weedy R. sativus in agrestal and ruderal environments, increasing the chances for introgression of crop alleles into weed populations. This is the first report of intraspecific crop-weed hybridization in R. sativus.
... Owing to their rapid water uptake (particularly in water-limited habitats), high growth rates, dispersal capabilities, and ability to thrive in areas with altered soil nutrient resources, synanthropic species (later termed weeds) frequently invade newly-formed habitats. A few weeds and invasive plants actually evolved from domestic ancestors (Ellstrand et al., 2010). The latter authors note that while the distinction between weeds and invasive plants is often clear, it is occasionally fuzzy or arbitrary (cf. ...
... De-domestication or feralization, which challenge the concept of plant domestication and further crop evolution as a death end, remains under-investigated though feral animal and plants have been known since the introduction of agriculture and are now becoming ubiquitous worldwide (Mabry et al., 2021). Feralization refers to domesticated species that escaped crop husbandry and continue growing in the wild (Ellstrand et al., 2010), but should not be seen just as a domestication reversal, and rather it must be understood as affected by various factors including novel selection pressures (Gering et al., 2019). As such it should be regarded as an extension of crop evolution (Wu et al., 2021). ...
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Underutilized pulses and their wild relatives are typically stress tolerant and their seeds are packed with protein, fibers, minerals, vitamins, and phytochemicals. The consumption of such nutritionally dense legumes together with cereal-based food may promote global food and nutritional security. However, such species are deficient in a few or several desirable domestication traits thereby reducing their agronomic value, requiring further genetic enhancement for developing productive, nutritionally dense, and climate resilient cultivars. This review article considers 13 underutilized pulses and focuses on their germplasm holdings, diversity, crop-wild-crop gene flow, genome sequencing, syntenic relationships, the potential for breeding and transgenic manipulation, and the genetics of agronomic and stress tolerance traits. Recent progress has shown the potential for crop improvement and food security, for example, the genetic basis of stem determinacy and fragrance in moth bean and rice bean, multiple abiotic stress tolerant traits in horse gram and tepary bean, bruchid resistance in lima bean, low neurotoxin in grass pea, and photoperiod induced flowering and anthocyanin accumulation in adzuki bean have been investigated. Advances in introgression breeding to develop elite genetic stocks of grass pea with low β-ODAP (neurotoxin compound), resistance to Mungbean yellow mosaic India virus in black gram using rice bean, and abiotic stress adaptation in common bean, using genes from tepary bean have been carried out. This highlights their potential in wider breeding programs to introduce such traits in locally adapted cultivars. The potential of de-domestication or feralization in the evolution of new variants in these crops are also highlighted.
... Studies of local adaptation in model or near-model organisms have been an important source of insights in the past (Leinonen et al., 2009), as have feral species (Franks et al., 2007), but there are abundant opportunities for more work in this area, especially in the genomic era (Saastamoinen et al., 2018). Feral organisms also present an opportunity to investigate invasion ecology, including eco-evolutionary questions, as many feral organisms are also invasive (Ellstrand et al., 2010). This work might include predictive models to anticipate future invasion and habitat suitability and characterization of the features that tend to make feral plants such effective competitors in certain environments. ...
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Societal Impact Statement: Given the rapidly increasing drought and temperature stresses associated with climate change, innovative approaches for food security are imperative. One understudied opportunity is using feral crops—plants that have escaped and persisted without cultivation—as a source of genetic diversity, which could build resilience in domesticated conspecifics. In some cases, however, feral plants vigorously compete with crops as weeds, challenging food security. By bridging historically siloed ecological, agronomic, and evolutionary lines of inquiry into feral crops, there is the opportunity to improve food security and understand this relatively understudied anthropogenic phenomenon. Summary: The phenomenon of feral crops, that is, free-living populations that have established outside cultivation, is understudied. Some researchers focus on the negative consequences of domestication, whereas others assert that feral populations may serve as useful pools of genetic diversity for future crop improvement. Although research on feral crops and the process of feralization has advanced rapidly in the last two decades, generalizable insights have been limited by a lack of comparative research across crop species and other factors. To improve international coordination of research on this topic, we summarize the current state of feralization research and chart a course for future study by consolidating outstanding questions in the field. These questions, which emerged from the colloquium “Darwins' reversals: What we now know about Feralization and Crop Wild Relatives” at the BOTANY 2021 conference, fall into seven categories that span both basic and applied research: (1) definitions and drivers of ferality, (2) genetic architecture and pathway, (3) evolutionary history and biogeography, (4) agronomy and breeding, (5) fundamental and applied ecology, (6) collecting and conservation, and (7) taxonomy and best practices. These questions serve as a basis for ferality researchers to coordinate research in these areas, potentially resulting in major contributions to food security in the face of climate change.
Bread wheat provides an essential fraction of the daily calorific intake for humanity. Due to its huge and complex genome, progresses in studying on the wheat genome are substantially trailed behind those of other two major crops, rice and maize, for at least a decade. With rapid advances in genome assembling and reduced cost of high-throughput sequencing, emerging de novo genome assemblies of wheat and whole-genome sequencing data are leading a paradigm shift in wheat research. Here, we review recent progress in dissecting the complex genome and germplasm evolution of wheat since the release of the first high-quality wheat genome. New insights have been gained in the evolution of wheat germplasm during domestication and modern breeding progress, genomic variations at multiple scales contributing to the diversity of wheat germplasm, and complex transcriptional and epigenetic regulations of functional genes in polyploid wheat. Genomics databases and bioinformatics tools meeting the urgent needs of wheat genomics research are also summarized. The ever-increasing omics data, along with advanced tools and well-structured databases, are expected to accelerate deciphering the germplasm and gene resources in wheat for future breeding advances.
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Grapes are one of the most common agricultural crops in the world. Currently, the analysis of genotypes directly at the DNA level is considered to be the most accurate method for studying the plant gene pool. The study of wild vines and ancient varieties in various regions of viticulture is an important direction of research in this field. The purpose of this work was to study the population of wild grapes growing on the territory of the Utrish Nature Reserve on the Black Sea coast of Krasnodar Region. The territory of the reserve is of interest as it is a site of ancient settlements, and the environmental conditions are suitable for the growth of wild grapes. During the survey of the territory, 24 samples of wild grapes were found, which were described according to the main morphological characteristics and analyzed by the molecular genetic method. The found vines were genotyped using 15 DNA markers, including nine commonly used for DNA fingerprinting (VVS2, VVMD5, VVMD7, VVMD25, VVMD27, VVMD28, VVMD32, VrZAG62, VrZAG79) and VVIb23, which allows determining hermaphrodite and dioecious vines. Statistical processing of microsatellite loci polymorphism data was carried out using the GenAlEx 6.5 program. The genetic relationships of the studied vines were evaluated using the PAST 2.17c program. The samples were found to be morphologically and genetically polymorphic. The number of alleles identified in the sample varied from 5 to 18 and averaged 8 alleles per locus. Statistical processing of DNA analysis data made it possible to identify two genetically different populations among the wild discovered vines. An assessment of genetic similarity of the found vines with some local varieties of geographically close viticulture regions, rootstocks and representatives of Vitis sylvestris from other territories was made. One of the populations found in the Utrish Nature Reserve is close to a number of V. sylvestris genotypes, the DNA profiles of which are presented in the Vitis International Variety Catalogue.
Integrity of biodiversity, ecosystems, and the environment is essential to guarantee the provision of ecosystem services, which is key for food security and the well-being of all forms of life. The possibility of deliberately manipulating organisms’ genomes for the benefit of human beings has raised several concerns. Biodiversity loss, disturbance of ecosystems, and genetic makeup of wild populations, as well as negative impacts on non-target organisms, are some of them. Cisgenesis was proposed as an alternative of genetic modification that respects species barriers; therefore, it is expected that it could overcome some limitations of both traditional and novel plant breeding techniques, as well as some challenges that modern agriculture faces. Given the importance to safeguard biodiversity, ecosystems, and environment while new developments are made, the possible positive and negative impacts of cisgenics on these three components are discussed here. Impacts equivalent to those that occur naturally or because of traditional breeding of crop plants are also analyzed. This chapter shows that cisgenics constitute a promising alternative that deserves further consideration and adoption, and that it is important that these developments are accompanied by sustainable agricultural practices.KeywordsAgricultural biotechnologyCisgenesisGenetic engineeringPlant breedingSustainable agricultureFood security
Introgression is the incorporation of a gene from one organism complex into another as a result of hybridization. A major concern with the use of genetically modified (GM) plants is the unintentional spread of the new genes from cultivated plants to their wild relatives and the subsequent impacts on the ecology of wild plants and their associated flora and fauna. The book reviews these issues, focusing on the ecological and evolutionary effects of introducing GM cultivars. It presents a summary of the current knowledge state of crop-wild relatives hybridization and introgression, and the measurement and prediction of their consequences. As a result it represents a major contribution to the debate about the risks of GM crops and measures, such as post commercialization monitoring, required to determine the longer term impacts of GM crops on ecosystems. The book presents edited and revised presentations given at a conference of the same name, organized in January 2003 by the University of Amsterdam (Netherlands) and the Robert Koch Institute (Germany), on behalf of the European Science Foundation funded programme for Assessment of the Impacts of Genetically Modified Plants (AIGM).
Humans have deliberately spread plants worldwide for millennia. The exchange of plants between different and often distant regions first became a mass global phenomenon in the post-Columbian era. Europeans introduced their cultivated and ornamental plants to the newly settled areas and in return made use of the biological wealth of the new regions for introductions into Europe (26,32,91,153). The scale of the introductions corresponded to the extent of the newly discovered regions. First Mediterranean and American species were usually introduced to central Europe, then species from Asia, and later Australian and African species (74,117).
Finger millet (Eleusine coracana (L.) Gaertn. subsp. coracana) is cultivated in eastern and southern Africa and in southern Asia. The closest wild relative of finger millet is E. coracana subsp. africana (Kennedy-O'Byrne) Hilu & de Wet. Wild finger millet (subsp. africana) is native to Africa but was introduced as a weed to the warmer parts of Asia and America. Derivatives of hybrids between subsp. coracana and subsp. africana are companion weeds of the crop in Africa. Cultivated finger millets are divided into five races on the basis of inflorescence morphology. Race coracana is widely distributed across the range of finger millet cultivation. It is present in the archaeological record of early African agriculture that may date back 5,000 years. Racial evolution took place in Africa. Races vulgaris, elongata, plana, and compacta evolved from race coracana, and were introduced into India some 3,000 years ago. Little independent racial evolution took place in India.
We describe a model-based clustering method for using multilocus genotype data to infer population structure and assign individuals to populations. We assume a model in which there are K populations (where K may be unknown), each of which is characterized by a set of allele frequencies at each locus. Individuals in the sample are assigned (probabilistically) to populations, or jointly to two or more populations if their genotypes indicate that they are admixed. Our model does not assume a particular mutation process, and it can be applied to most of the commonly used genetic markers, provided that they are not closely linked. Applications of our method include demonstrating the presence of population structure, assigning individuals to populations, studying hybrid zones, and identifying migrants and admixed individuals. We show that the method can produce highly accurate assignments using modest numbers of loci—e.g., seven microsatellite loci in an example using genotype data from an endangered bird species. The software used for this article is available from