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African
Crops News Home
Dainty but
dangerous. A plant of Striga hermonthica in full blown
with beautiful flowers, while the susceptible maize variety withers
under the attack of the parasitic weed |
Striga
tolerant maize varieties (left). Note the green leaves, while the
susceptible varieties (right) are wilting |
Improved
maize varieties resistant to Striga hermonthica (left)
Susceptible varieties (right). (Pic. IITA) |
Striking out
Striga parasitic weeds with resistant maize cultivars
Taye Babaleye and
Abebe Menkir, International Institute for Tropical Agriculture
Maize is a staple
food crop in more than 18 countries and a very important crop in 13 others
in sub-Saharan Africa. Maize remains the favorite of the African farmers
because it is the first "insurance" food crop against hunger at the
beginning of the rainy season. It is easily converted into well-accepted
local food products, such as gruels, porridges and pastes, and consumed
every day and as weaning foods for babies. Striga poses a serious
threat to maize production in Africa. The problem of Striga is
intensifying across regions in Sub-Saharan Africa because of deteriorating
soil fertility, shortening of the fallow period, expansion of production
into marginal lands with little nutrient input and increasing trend towards
continuous cultivation of one crop in place of traditional rotation and
inter-cropping systems.
The problems
caused by Striga are unique because of the close biological
association of the parasitic weed to its host plants. It devastates maize
and other cereals which are the major staple foods for over 100 million
people and causes annual losses of about US$7 billion. The Striga
problem is intimately associated with increased mono cropping, reduced
fallow periods, and low soil fertility, and is an indicator of environmental
degradation. Effective control of Striga is very difficult because
the parasitic weed (i) produces millions of tiny seeds that can remain
viable in the soil for up to 20 years, (ii) attaches itself to the host root
and is completely dependent on the host for water and nutrients while it is
underground; (iii) causes about 75% of its overall damage to its host while
it is still underground; and (iv) emerges above soil level usually after the
farmer has completed the last weeding.
A major
breakthrough has, however, been recorded on the control of this stubborn
weed through the development of Striga resistant maize varieties by
scientists at the International Institute of Tropical Agriculture (IITA).
With the introduction of the improved maize varieties efforts to ensure food
security and income generation for maize farmers are yielding good results.
Hitherto, in several countries of sub-Saharan Africa, the Striga
problem has reached epidemic proportions. For the past six years, improved
maize varieties resistant to the obnoxious weeds have become a toast of
farmers in the continent. The abandoned farms are now being re-visited,
re-dressed, and planted into the new maize varieties without much fear of
Striga infestation.
The Striga
resistant maize varieties were first introduced to farmers at the Federal
Capital Territory (FCT), Abuja in collaboration with the national
agricultural research systems (NARS) in 2001. The resistant maize varieties
have ability to suppress the development of Striga, and double maize
yields in farmers' fields. The varieties include ACR 94 TZE, COMP.5-W, an
early maturing variety, IWD-STR, an intermediate maturing variety, and ACR
97TZL COMP.1-W, a late maturing variety. Several field days have since been
organized in collaboration with national agricultural research systems in
Nigeria to create awareness on the improved varieties which are being
introduced to farmers to complement other integrated control measures.
After the success
of the Striga resistant maize technology in multi-location trials in
Nigeria, Benin, Burkina Faso, Cameroon, Cote d’Ivoire, Ghana and Mali by the
Semi-Arid Africa Agricultural Research and Development (SAFGRAD), farmers
are now putting more confidence into maize farming and they are even
increasing their farm holdings. In virtually all of the trial locations,
maize yields doubled from an average of one ton per hectare to more than 2
ton per hectare. To effect a sustained Striga control strategy,
SAFGRAD, with funding support from the Korean government established in
2002-2004 a Striga Task Force (STF), to introduce the Striga
resistant maize varieties in combinations with other control options to
minimize the adverse effects of the noxious weeds in maize fields. The
approach has greatly enhanced the availability of the resistant maize
varieties to communities. The SAFGRAD approach to Striga control was
also aimed at complementing efforts by the system wide Integrated Pest
Management (IPM) techniques of the Consultative Group on International
Research (CGIAR). Already several requests are being made to IITA to extend
the improved maize varieties as important components of an integrated pest
management strategy for controlling the weeds in other areas of Africa.
IITA maize
breeder, Dr. Abebe Menkir, said that the development of Striga
resistant maize varieties was not easy. “IITA started screening a large
collection of maize germplasm from diverse sources for tolerance to
Striga. The advances made in the development of artificial field
infestation techniques at IITA have facilitated the identification of
tolerance to Striga from these sources of germplasm. The early
breeding work at IITA focused on search for tolerance to Striga
hermonthica and sources of tolerance were identified from both temperate
and tropical maize germplasm. Working within these sources of germplasm,
IITA breeders made significant progress in developing open-pollinated
varieties, inbred lines, as well as experimental hybrids with good level of
tolerance to S. hermonthica.
Furthermore, IITA
has made a significant shift in emphasis towards selection of maize
germplasm for resistance to Striga, to reduce the number of emerged Striga plants. In contrast to tolerance, the selection and
cultivation of resistant cultivars reduces reproduction of seed of the
parasite thereby contributing to depletion of Striga seeds from the
soil. Considerable progress has been made with this approach as excellent
sources of resistance have been obtained from wild species, African
landraces and elite tropical germplasm. Intensive screening of these sources
of germplasm in the field under artificial infestation have yielded
open-pollinated varieties, inbred lines and hybrids with resistance to
Striga as demonstrated in repeated field tests conducted in different
locations”, he said.
The distribution
and testing of maize varieties resistant to S. hermonthica in 11 countries
of West and Central Africa was made possible through the collaborative
efforts of the West and Central African Maize Network (WECAMAN), working
with the national agricultural research systems (NARS) in the sub-region. He
said with funding provided by the United States Agency for International
Development (USAID), UNDP and IFAD, trials were organized in several
locations to demonstrate the effectiveness of the open pollinated varieties
and hybrid maize varieties resistant to the parasitic weed.
With the
development and availability of the resistant maize varieties to S.
hermonthica, a new hope is on the horizon for the farmers who are now
willing to go back to their abandoned farms and embark on maize production
because of their confidence in the new maize varieties. This will contribute
to food security and income-generating opportunities to people that depend
on maize as an important food crop.
For further
details please contact:
Taye Babaleye
Abebe Menkir
Public Relations
Manager Maize Breeder
IITA, Oyo
Road IITA, Oyo Road
PMB 5320
PMB 5320
Ibadan.
Ibadan.
Email:
t.babaleye@cgiar.org Email:
a.menkir@cgiar.org
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