RA 00110.pdf - OAR@ICRISAT

dew may reach 40% in certain regions (Scheuring
1980), while Raghuva infestations and shibras are
responsible for losses up to 27-37% in Niger (Mclntire
1982). Low yields of local or improved cultivars can
also be attributed to climatic conditions, especially
in the Sahelian zone.
Abiotic Constraints
Soils
Pearl millet is grown on soils that are generally poor
in organic matter and nutrients (Stoop et al. 1982).
These shallow soils are mostly sandy with a low
phosphorous content, sometimes lateritic; clay content
is always low and of poor quality (kaolinite);
and the cation exchange capacity is low. Crust formation
is frequent and impedes emergence. At the
start of the rainy season, soil temperatures are high
with frequent sand storms, so that the seedlings are
often buried under the sand, and crop establishment
is poor.
Cultural Techniques
Crop cultivation in the Sahel is usually manual and
based on hand tools such as the "daba" and "hilaire."
The use of animal traction is rare—about 30% in
Mali and less than 10% in Niger—so that tillage
operations are carried out only on a few farms.
Plants are not thinned due to lack of time, leading to
high within-hill populations and competition between
plants. A 1-week delay in the first weeding operation
can result in a 10% yield loss (Matlon 1983). Hence,
improved cultural techniques alone can increase
production by 40% (Siband 1983).
Climate
The climate in the region is characterized by two
distinct seasons: a dry season with no rainfall and a
wet season extending 3-5 months. A north-south
gradient of increasing rainfall can be observed in
each country.
In the Sudanian zone, the rainy season is generally
longer with less rainfall variation. But in the Sahelian
zone, the wet season is characterized by highly
variable rainfall amounts and distribution, especially
at the beginning and end of the season. It is
under these conditions that millet is usually grown
and is frequently replanted—up to three times, due
to poor crop establishment.
Biotic Constraints
Insect Pests
Refer to NDoye and Gahukar's paper, these proceedings.
Diseases
Mildew (Sclerospora graminicola). Not much information
is available on yield losses due to this
disease (Scheuring 1980, Diaby 1982), but it is
generally considered to be the most important pearl
millet disease in West Africa (Delassus 1964, Girard
1975). Local cultivars exhibit highly diverse tolerance
to mildew. West Africa has important sources
of resistance, particularly in northern Nigeria, southern
Niger, Burkina Faso, and Mali (Williams and
Andrews 1983).
Ergot (Claviceps fusiformis). This disease rarely
occurs in the Sahel but is frequent in wetter zones
(Gambia, Ghana). Most local cultivars are usually
not badly affected by ergot (Selvaraj 1980).
Smut (Tolyposporium penicillaria). Although smut
is the second most important millet disease in Africa,
local crops are less affected by it.
Weeds
Weed control is important since yield losses from
weeds are estimated at 25% but because of their
height, landraces are able to successfully compete
with weeds. Weeds other than those found in rainfed
crops are:
Striga (S. hermonthica). Yield losses from this
parasitic weed can reach 60-70% in certain countries
(NDoye 1984), and this is one of the most important
factors that reduces pearl millet yields in the Sahelian
zone.
Shibras (P. stenostachyum). Shibras are a weedy
form resulting from a wild millet x cultivated millet
cross. In certain fields their occurrence (20%) can
reduce yields of the infested crop, but eradication of
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