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September, 2008
Source:
CIMMYT E-News, vol 5 no.
9, September 2008
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The
dramatic difference between Striga-free (left-rear) and
Striga-infested (right-front) maize crops. |
Looks can deceive. Striga, a
deadly parasitic plant, produces a lovely flower but sucks the
life and yields out of crops across Africa and Asia. A new
strain of improved maize seed is helping farmers reclaim their
invaded crop lands.
Striga, which typically attacks cereal crops, launches its
takeover from the ground up: its deadly seedlings attach to
sprouting maize plants and begin siphoning off water and
nutrients before either plant emerges from the soil. The
parasite also poisons its host, further stifling crop
development.
Worse, Striga seems to seek out the farmers least suited to
control it.
“Striga thrives in low-fertility soils, which are typically
owned by the poorest farmers,” says Fred Kanampiu, CIMMYT maize
agronomist. National experts estimate 14% of the maize area in
sub-Saharan Africa is infested with Striga, amounting to 3.64
million hectares.
Big benefits seen for Kenya
Work by a multilateral partnership has resulted in a promising
Striga control measure that has recently started moving from the
laboratory to farmers' fields. The practice is based on a type
of maize with a natural mutation that allows it to resist the
chemical imidazolinone—active ingredient in many herbicides.
Seeds of this imidazolinone-resistant (IR) maize are coated with
a herbicide and, when sown, the coated seed kills sprouting
Striga, allowing the crop to flourish.
“Economic studies estimate that if a third of the
Striga-infested area were planted with herbicide-coated seed,
benefits to farmers in Kenya would be between USD 51 million and
102 million, after production costs,” says Kanampiu, who
coordinates the Striga Management Project. “This would be topped
off by a yield effect of similar magnitude, because the
herbicide resistance comes in seed of improved, locally-adapted
varieties.”
A complex, multilateral effort
The idea of using herbicide-resistant maize to control Striga
was first proposed by the Weizmann Institute of Science in
Israel in the 1990s. CIMMYT worked with that organization, as
well as the Kenyan Agricultural Research Institute (KARI), BASF,
the African Agricultural Technology Foundation (AATF),
non-governmental organizations, and seed companies including
Pioneer to develop, evaluate, and spread the practice,
particularly among small-scale farmers for whom other control
methods, such as spraying, are expensive or impractical. A key
part of the work involved developing high-yielding,
locally-adapted maize varieties that were also herbicide
tolerant. The coating method was fine-tuned by Weizmann and the
company Hi-Cap Formulations.
Support for more recent tests and promotion came from the German
Federal Ministry for Economic Cooperation and Development (BMZ),
the International Fund for Agricultural Development (IFAD), and
the Rockefeller Foundation. By 2006 CIMMYT and KARI scientists
had provided almost 300 herbicide-tolerant maize varieties for
regional testing. Studies in randomly-selected farmers’ fields
showed that with 30 grams (a little more than 1 ounce) of
imazapyr herbicide per hectare as a seed coat in heavily
infested fields, Striga was reduced by 81% and farmers enjoyed a
63% net return.
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The
first commercial IR maize hybrid |
Striga meets its match
“The IR-maize reduces the Striga seed bank in the soil,
lessening the need for future Striga control measures,” says
Gospel Omanya, a Stewardship Manager from AATF, which is leading
region-wide public awareness campaigns, field testing, and risk
assessment. In addition, smallholder farmers who have tested the
new maize and seed-coating practice on their land have obtained
as much as a five-fold increase in grain yield.
Positive results like these led to the release of five IR
varieties to farmers in Kenya, and nine other varieties are in
performance evaluations for eventual release in Tanzania and
Uganda.
More than 50,000 packages of IR-maize seed were distributed to
farmers at 140 locations in Kenya for comparison with other
Striga control practices. AATF surveyed more than 5,000 farmers
and found they overwhelming favored the IR-maize seed. At least
10 seed companies, including Western Seed Company in Kenya and
Tanseed International in Tanzania, are using IR maize and 60
tons of certified seed were marketed during 2007-2008.
“It was years of intense research and collaboration between
partners dedicated to a unified objective, in addition to a
willingness to invest human and financial resources, that
allowed this concept to become a reality,” says Kanampiu. "The
practice offers real, life-changing benefits for subsistence
farmers like many in western Kenya, who tend 1.5 hectare plots
of mostly maize just to feed their families. Their crops are
normally so decimated by Striga that they harvest barely
enough."
Meanwhile, CIMMYT is working with the International Institute of
Tropical Agriculture (IITA), a leader in the effort to identify
and breed maize strains that contain genetic resistance to
Striga. The aim is to offer farmers yet another way of
controlling this lovely but lethal pest.
For more information, contact Fred Kanampiu (f.kanampiu@cgiar.org).
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