By Dr. Mohammed Sa’id Berigari, Senior Soil and
Environmental Scientist, USA, 20/05/2012.
Which USA Crop Wild Relatives Are Identified
as Most Useful?
Adapting agriculture to climate change is one of the
greatest challenges of 21 st century facing humanity. By 2050 world population is
expected to exceed 9 billion. We will reach
the limits of the world arable land expansion and other resources for
agriculture. Is it possible to meet the demands
of such a large population for food, shelter, and fiber without huge increases
in agricultural products? The answer is
definitely no. Therefore, it is an urgent matter to plan now for new varieties
of crops that can adapt to climate change, resist biotic stresses such as pests
and diseases; and tolerate abiotic stresses such as drought, cold, heat, and
other conditions; and to a great extent
sustain high yields with desirable qualities.
The crop wild relatives (CWR) are wild plant taxa
closely related genetically to crop plants.
CWR posses a wide range of biodiversity i.e. genetic variation in
contrast to the cultivated crops for which domestication has tended to create
genetic bottleneck. Moreover, CWR
represent an excellent source of genomes for plant breeders to utilize their
potentials for developing desirable traits into cultivated crop. And CWR in
general have been identified as critical useful groups of plants for
agricultural and environmental sustainability and improvement.
However, the survival of some CWR is alarmingly threatened
by irreversible agro-environmental practices, destruction and fragmentation of
their habitat, and climate change.
Therefore, concerted efforts are needed to establish global networks for
the in situ conservation and
protection of CWR.
A historical approach is appropriate to follow here for
the reader to appreciate the contributions of numerous scientists in this field
of vital importance to food security of the entire world population now and in
the foreseeable future.
N.E. Hansen,
a botanist, brought a wild Siberian alfalfa species to the US in the late 1800s
with expectations of its potential to survive extreme cold and drought, thus,
to benefit farmers of the northern Great Plains, which he called” My American
Siberia”. Farmers sowed the unusual, yellow-flowered
alfalfa into their farms, while plant breeders used it to breed winter-
hardiness into cultivated blue-flowered alfalfa. To Hansen’s surprise the yellow-flowered
alfalfa escaped cultivation and went wild, adapting to the Great Plains
environment and generating greater people’s interest. After many decades a rancher from South
Dakota in 1997 reported that wild populations of yellow-flowered alfalfa were
boosting forage production and fattening his cattle. The rancher began exploring the plant’s
ability to restore degraded soils of his pasture. Plant breeders also gave the
yellow-flowered alfalfa a second chance, using it to develop a new variety of
alfalfa adapted to the cold and dry rangeland of the region.
Meanwhile,
wild populations of yellow-flowered alfalfa had spread to the Grand River
National Grassland in northwestern South Dakota, and their ability to displace
other species bewildered scientists what to do.
Should they allow this wild species to become a part of the
landscape? Or should they eradicate it
to protect native communities? For either option the plant seemed hardly to
require such actions. “Or does it?” That is the question went around “crop wild
relatives”: species that are genetically
related to domestic crops, forages, ornamentals, medicinal herbs, and other
beneficial plants but are not domesticated.
Some are common and weedy like the yellow-flowered alfalfa, while others
like the walnut relative, Juglans hindsii,
are endangered globally.
Stephanie
Green, a plant geneticist, claims that the lack of attention has put CWR in a
precarious position. According to a recent estimate one fifth of all wild
plants are now threatened with extinction, that is before the potential
influence of climate change is included in that estimate. Despite world initiatives to conserve biodiversity,
according to Greene, “it is recognized that crop wild relatives have been left
behind.”
She is
currently leading an effort to tally the CWR in USA, identify which are of
greatest importance to global and American agriculture, and to initiate a
nationwide strategy for protecting them both in gene banks as ex situ and in their natural habitat as in situ. However, conserving CWR is the first step
forward. The real objective is to obtain
their diverse genetic materials and allow plant breeders to adapt crops to
tolerate increased drought, intensified disease pressure, and climate change.
Greene started that task while CWR were and
still are threatened by climate change just like all wild species , they are
also the same plants that could help us adapt our food systems to the new
conditions.
Greene after
reviewing scientific literature and other resources listed CWR growing in USA
and collected information about them including their conditions in the wild and
the crops they used to improve. She
also assessed how closely related each wild relative was to its respective crop
and obtaining help in this area from John Wiersema, a plant taxonomist with
USDA. Wiersema is the manager of
taxonomic information for National Plant Germplasm System’s database of crop genome,
known as GRIN. Along similar lines
Wiersema and coworkers began a project in 2008 of identifying methodically CWR
from the entire world and classifying them taxonomically. The idea was that the closest relatives should
be more suitable and the easiest for plant breeders to use.
Wiersema
said” that is true in traditional breeding and perhaps even true with advanced
genetic techniques.” And he also stated “the most related plants will offer the
best chance to transfer favorable genes into crops.”
Greene
started to put together an inventory and when she finished, her inventory
contained over 3,000 species, subspecies and varieties of the CWR in the US and
she emphasized the need for the next step in Maxted’s strategy which is setting
up priorities for conservation of CWR. Colin Khoury, a former student of Maxted
came along to work with Greene on CWR of the US. He started on prioritization
plan from Colombia, South America where he currently works for the International
Center for tropical agriculture (CIAT).
Khoury’s
method takes into account a number of factors.
Ensuring food security is his major objective, thus US wild relatives of
the 70 most important food crops of the world make up the bulk of his
prioritization list. And he added to the
list wild relatives of what he named” iconic U.S. Crops” plants of value
primarily to American agriculture, including sugar maple, pecan, wild rice, and
Echinacea. Khoury reduced the list further where he
identified the very closest relatives of crop plants or” primary genetic
relatives” and some of the CWR that are rare or endangered species. After intensive reviews by curators, plant
breeders, and others the list now contains about 300 taxa that seem to have the
greatest potential to contribute to crop improvement.
Which crops
in the US have valuable wild relatives?
According To Greene Sunflower is a major agronomic crop plant that has
originated in North America. Her list
includes the fruit crops: cranberry,
blueberry, and currant; the nut crops: pecans, hazelnut, and walnut; and the stone
fruits: almond, peach, and cherry. And
also, lettuce, onion, bean, squash, sugarcane, and grape have rich native genomes
in the US, all of which surprised Greene.
“ The
general consensus is that CWR taxa are usually found in the Mediterranean Basin
or in the Fertile Crescent in the Middle East and that North America is kind of
depauperate ” according to Greene.
However, North America has a good list of CWR. That is why Maxted argues for setting global
priorities for CWR protection but also establishing national conservation
strategies too. The most important CWR are found in the Vavilov Centers and in
terms of food security they should be focused internationally. However, each country has some CWR and is the
source of biodiversity community for which each country should show the
ecosystem service value in their native
plants.
According to
Wiersema people also assume only native plants, such as sunflower in the US are
the critical CWR. However, the US
inventory contains dozens of non-native CWR taxa that developed valuable traits
as they became adapted or naturalized to North American environment. Wiersema was surprised to find in the US that
some genetic resources are weedy, non-native plants that breeders considered
interesting. This suggests as Wiersema
stated that there’s still an opportunity for evolution of naturalized species
even though they have not been in their current habitat for a long time and
that scientists who look for crop diversity only in places like the Vavilov
Centers may overlook some important genetic resources elsewhere.
Looking for and Identifying the Gabs-
then Filling Them
With the key
US crop wild relatives being identified, Khoury plans to use a method developed
by Maxted called “gap analysis” to determine the exact conservation action
needed for each plant on the list.
During the first stage Khoury uses database information and Geographic
Information Systems (GIS) mapping models to predict the full geographic range
of each CWR taxon across the US. Within
those ranges, he will determine the places where each CWR has been collected
previously, if any, and the locations where they are currently protected: in a
national park or on the US Forest Service land.
According to Khoury the idea behind this
effort is to find “interesting gaps” in collection and conservation, whether
they are taxonomic, geographic, or environmental. Large taxonomic gaps in gene bank collection
are known to exist. For example out of
450,000 plant varieties, or accessions, currently stored in by the National
Plant Germplasm System, fewer than 3% are wild plants collected in the US. But obtaining one of each missing CWR taxon
also won’t be enough, said Wiersema.
“We want not
just to conserve these wild relatives, but also to conserve the diversity of
CWR, which is something that‘s probably not paid attention to in conservation
generally” said Wiersema. It is vital to
preserve CWR with very limited distributions, such as Cucurbita okeechobeensis, a threatened squash relative that grows only along the shore of Florida’s Lake
Okeechobee. It is critical to conserve weedier CWR, but also those more widely distributed CWR
across the full range of the environment where they occur-especially in places
where they may have developed useful traits such as tolerance to abiotic
parameters of drought, heat, or salinity; or resistance to biotic agents such
as pests, bacteria, fungi, or viruses.
“Our goal is
to preserve all that genetic variability because for crop breeding purposes we
are likely going to need it” said Wiersema, “
When Khoury
locates the critical gaps, the National Plant Germplasm System will try to fill
them by collecting CWR seeds in US and other genetic materials for their backup
in gene bank or ex situ collections. Meanwhile,
both Maxted and Khoury are engaged in a similar task at the international
level, spearheaded by the food security foundation which is known as the Global
Crop Diversity Trust (GCDT).
Gene bank
collections are indispensible, but they also represent mere” snapshots in time”
of adapting and evolving plants continuously.
This is why Wiersema, Khoury, and others advocate a second complementary
approach of protecting CWR plants in situ.
The
advantage of keeping the CWR in situ
is to allow species to continue evolving and helps protect their native habitat
as well as associate species. According
to Maxted in country after country in situ
protection has proven harder than one would expect. People who want to conserve CWR can’t just
set up their conservation areas. They
must work with managers of national, state or provisional parks; national
forests; and other lands to ensure that existing conservation strategies are
expanded to include CWR. And this will
require cooperation and understanding between agricultural scientists and plant
conservation specialists. But getting
those two groups to communicate with each other is very difficult as Maxted
pointed out because of their different aims.
Maxted’s CWR
management plan is currently moving ahead with UK conservation authority and
still has a real chance of establishing the first reserve for CWR genetic
diversity in Europe. According to
Greene, the National Plant Germplasm System and US Forest Service signed a
memorandum of understanding, outlining how the two parties can cooperate to
protect CWR on national forest lands.
There is
still much more to do. The human
population is growing rapidly and habitat for CWR is shrinking due to
urbanization and agriculture expansion.
And plant distribution is shifting in response to higher global
temperatures. It takes 10 years or more
for a novel source of germplasm to get to farmers as an improved plant
variety-leaving breeders valuable time now to adapt crops to climate change.
Khoury
pointed out that the window of opportunity is narrowing for securing these
genetic resources so that they can be safe but also be used. Therefore, it is really time to move forward
and conserve these indispensible resources.
References
Fisher, M. 2012.
Crop wild relatives and their potential for crop improvement. (Crops,
Soils, Agronomy) CSA News, Crop Sci. Soc.Amer., Soil Sci.Soc.Amer., Amer.Soc. Agron. May issue: 4-10.
Greene, S.L.
2010. Fruit and nut crop wild relatives in the United States: a surprisingly rich resource. Submitted to Acta Horticulture, Publication
Acceptance Date: June 4, 2011. Interpretive Summary is available in ARS Web
site under her name.
Khoury, C.;
Greene, S.L.; Castaneda, A.; and Nora, P.
20011. Initial steps toward a
national conservation strategy for crop wild relatives of the United
States. Meeting Abstract. p 240
Khoury, C.
and L. Guarino. 2010. Back to the roots:
Wild genes for food security. Global Crop Diversity Trust, Rome, Italy.
3 pp.
Maxted, M.
and S.Kell. 2009. Establishment of global network for in situ conservation of crop wild
relatives: status and needs. FAO Commission on Genetic Resources for Food
and Agriculture, Rome, Italy. 266 pp.
Vavilov,N.I.
1951. Phytogeographic basis of plant
breeding. In K.S.Chester, transl, the
origin, variation, immunity, and breeding of cultivated plants). Chronica Botanica 13: 14-54.
Wiersema, J.
and L. Blanca. 2001. World Economic Plants: a Standard Reference. Publ.CRC Press, Baca Raton, Florida. 536 pp.
No comments:
Post a Comment