Nairobi, Kenya
August 7, 2008
Every year the Striga weed
attacks and kills Africa’s most important food crops in more
than 40 million hectares of farmland often leaving farmers with
no harvest
Agricultural researchers have successfully identified and
transferred genes that confer resistance to Africa’s most deadly
weed (Striga) using the novel marker assisted selection
technique successfully for the first time in the history of crop
breeding in Africa.
Researchers have managed to confer resistance to Striga in
sorghum, overcoming a barrier that has for decades held back
scientists’efforts to protect key food crops - sorghum, millet,
maize and rice, from this destructive weed. These crops are
primary food sources for 300 million people across sub-Saharan
Africa.
Striga(Striga hermonthica), also known as witchweed, destroys
between 40 to 100 percent of a complete season’s crop, its
annual crop damage across Africa estimated at seven billion
dollars (US$7 billion). Currently, the weed threatens to wipe
out cereal crops in most of Western Kenya and Eastern Uganda,
national agricultural research institutes in the two countries
have warned.
“Scientists have searched for the solution to Striga damage
using a variety of methods, but without much success,” says Dr
Dionysious Kiambi, a molecular geneticist with the
International Crops Research
Institute for Semi-Arid Tropics (ICRISAT). “Through marker
assisted selection, we have determined the precise segments of
the sorghum genome known to confer Striga-resistance and have
transferred them to farmer-preferred varieties through
conventional breeding with very promising results”.
Marker assisted selection is a new technique which entails use
of genetic landmarks (markers) to tag and transfer specific
genes or group of genes that control characteristics of interest
such as improved crop productivity, resistance to diseases or
pests, or tolerance to stresses like floods and drought. This is
the first time the technology has been used successfully for
crop improvement in Africa.
ICRISAT scientists has been working with national and
international collaborators for several years experimenting with
marker assisted selection in search for Striga resistance genes
from other sorghum varieties conserved in gene-banks across the
world. They found one sorghum variety (N13), that is neither
high-yielding nor drought-tolerant, to possess the highly sought
after Striga-resistance genes.
Segments of the N13 sorghum DNA containing genes for
Striga-resistance were tagged with markers and crossed with
farmer varieties using conventional breeding. The use of markers
enabled scientists to precisely transfer only the Striga-
resistance genes to farmer-preferred sorghum varieties without
jeopardising farmer-desired characteristics such as
drought-tolerance and higher yields.
“We had to make sure that other genetic information from N13 was
not transferred to farmer varieties alongside the qualitative
trait loci with Striga-resistance. We were not replacing any
genetic components of farmer varieties, we are just adding to
it,” says Dr Kiambi. “The resulting variety is almost identical
to the original farmer variety plus the component that confers
Striga resistance.”
ICRISAT has been collaborating with scientists from the
University of Hohenheim in Germany and national agricultural
research institutes of Eritrea, Kenya, Mali and Sudan. The team
has to date created five Striga-resistant sorghum varieties
whose initial trials on-station have been able to ward off
Striga attacks, some as effectively as the donor parent, sorghum
N13. In Kenya, Mali and Sudan, scientists are currently testing
the new witchweed-resistant varieties in farmer fields.
Researchers in Africa have for decades experimented with a
number of “potentially successful” techniques for managing this
deathly weed including breeding for Striga tolerance in various
crops, promotion of rotational cropping of cereals with legumes
such as groundnuts, cowpeas and soybean in order to break the
weed’s breeding circle, as well as the use of biological and
herbicidal control methods.
Africa ’s resource-poor farmers manage Striga primarily by
weeding, a pointless, back-breaking activity which comes too
late. By the time the crop sprouts, the weed, whose seeds reside
in the soil, has long-since attached to plant roots and begun
sapping off plant nutrients in earnest. Striga is a prolific
seed producer, whose seeds lie dormant in the soil for up to two
decades.
Crop breeders are enthusiastic about marker assisted breeding
because it significantly reduces the duration required to
produce improved crop. While conventional breeding is a
hit-or-miss technique that requires scientists to wait for the
crops to grow to maturity in order to observe expression of
desired traits like Striga-resistance, marker assisted breeding
enables scientists to check for the transfer of the trait as
early as when the plant is only two weeks old, and focus on
plants with the desired trait. This has more than halved the
amount of time crop breeders need to develop improved varieties.
If the on-station results are successfully replicated on-farm,
Africa’s biggest cereal crop menace – Striga - may well be
reigned in, boosting agricultural production, food security and
farmer incomes across the continent.
The International Crops Research Institute for the Semi-Arid
Tropics (ICRISAT) is a nonprofit, non-political organization
that does innovative agricultural research and capacity building
for sustainable development with a wide array of partners across
the globe. Its mission is to help empower 600 million poor
people to overcome hunger, poverty and a degraded environment in
the dry tropics through better agriculture. ICRISAT, is one of
15 centers supported by the Consultative Group on International
Agricultural Research (CGIAR). For more information, visit
www.icrisat.org
The CGIAR, established in 1971, is a strategic partnership of
countries, international and regional organizations and private
foundations supporting the work of 15 international Centers. In
collaboration with national agricultural research systems, civil
society and the private sector, the CGIAR fosters sustainable
agricultural growth through high-quality science aimed at
benefiting the poor through stronger food security, better human
nutrition and health, higher incomes and improved management of
natural resources. For more information, please visit
www.cgiar.org . |
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