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www.iita.orgA member of CGIAR consortium
Research Technicians’ Training
Grain Legumes
Morphology, Physiology etc.
www.iita.orgA member of CGIAR consortium
Legumes are classified into three groups
- Caesalpinacea
- Mimosacea
- Papilionacea
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Important food leguminous crops:
• Soybean
• Cowpea
• Groundnut
• Common bean
• Pigeon pea
• African yam bean
• Bambara groundnut
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• All of these economically important grain
legume crops belong to the family Papilionacea
• As legumes they fix atmospheric nitrogen in
their root nodules
• Many benefit from inoculation with the
bacterium – Rhizobium
• Usually they do not need nitrogen fertilizers
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Uses of legumes
Pulses i.e. dry grains – cowpea, green gram,
common bean, pigeon pea, mung bean, Lima
bean etc.
Oil seeds – groundnut, soybean
Cover crops & manures – pueraria, lablab,
centrosema
Dyes – Indigofera, Pterocarpus
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Uses contd.
Livestock feed – cowpea haulm
Shade trees - Gliricidia
Ornamentals - Jacaranda, Cassia
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• Grains of legume crops are rich in
protein, minerals, starch/carbohydrates,
dietary fibre
• They complement amino acids in cereals
• Some grains have anti-nutritional
components
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Leaves are alternate and usually compound
Flowers are showy, irregular and mostly
hermaphrodites
Flowers have the standard petal, wings and
keel
Each anther has two locules dehiscing
lengthwise
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Usually 10 stamens
Anthers dehisce lengthwise to discharge pollen
Ovary with one locule is surrounded by the
stamens
Fruit/pod split along ventral suture or could be
non dehiscent
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As with other crops selection from primitive to
modern forms have resulted in:
Plants allocating more carbon and nitrogen
to fruits than to vegetative parts
Increased fruit and seed sizes
Fruit less prone to shattering
Reduced or lost seed dormancy
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Cowpea is the most important grain legume crop
grown in the dry savannah regions of Africa
The highest production comes from West Africa
Nigeria produces and consumes the highest
amount of cowpea grains
Yield is generally low due to abiotic and biotic
stresses
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Originated in Africa –
Highest level of genetic
diversity in sub-
Saharan Africa
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Cowpea grows in areas with rainfall of 400
mm to >1,200 mm
It is therefore adapted to drought prone
areas of the savannah
Most cowpea come from the sahel and sudan
savannah.
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• It has 11 pairs of chromosomes; 2N = 22
• Leaves are alternately arranged on stem
• Leaves are trifoliate
• Leaves are glabrous in cultivated lines,
hairy in some wild relatives
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• Petioles have swollen bases
• Stems are cylindrical, mostly green with
purple pigment at nodes or entire stem
surface.
• Plant habit could be erect, semi-erect or
prostrate.
• Stems climb when plant is shaded.
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Cowpea is typically day length sensitive
Plants flower early during short days
Long day length delays flowering but does not
prevent flowering
Most modern varieties are day length
insensitive
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Cowpea and soybean plants develop from seeds
• Plants go through seedling, vegetative and
reproductive stages of development
• Plants could be determinate or indeterminate
• Modern varieties are mostly determinate
• Indeterminate types produce more fodder
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Dry matter accumulation in cowpea
and soybean during vegetative and
early reproductive stages are
comparable
Higher leaf area duration (LAD)
resulted in more grain yield in
soybean than cowpea
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Leaf area index (LAI) = dimensionless
quantity that characterizes plant
canopies.
It is the one-sided green leaf area per
unit ground surface area (LAI = leaf
area / ground area, m2 / m2)
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Cowpea has strong tap root system
Roots can grow up to a depth of >1 meter
Roots are important in water and mineral
absorption and possibly drought tolerance
Roots have nodules in which live symbiotic
bacteria
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Cowpea symbiose with nodule bacteria
found across Africa
The bacteria – Rhizobium converts
atmospheric nitrogen to compounds that
host plant can assimilate
Cowpea can fix up to 150 kg N/ha
Supplies 80-90% of the host plant’s N needs
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Nitrogen fixed before flowering contributes
about 60% of the fruits total requirement for N
Leaves and nodulated roots in particular
contribute their mobilised N to the fruit
Petioles, stems and peduncles also contribute but
to a lesser extent
Remaining 40% required N in fruit come from
fixation after flowering
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Usually, indeterminate varieties fix more N
than determinate varieties
Late maturing varieties fix more N and leave
more in the soil after harvest – dropped leaves,
stems and underground roots release N
contained in them to the soil
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• Flowers are showy
• Could be white, yellow, light or deep
purple coloured
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• Flowers are borne on very short pedicels
attached to peduncles which vary in length
depending on the variety
• Inflorescence is axillary and crowded to the tip
of peduncles
• Cushion-like nectary is located between pairs of
flowers
• Peduncles develop from the nodes
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Flower buds light
coloured when
ready to open
Anthers dehisce
on day flower
opens
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Like all legumes most of the flower buds
drop in cowpea and soybean. Between 20
and 80 %
Only a few develop into pods
Number of pods per peduncle varies with
varieties but usually not more than
four/peduncle. There could be five or more
pods on some peduncles.
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Pods contain variable number of seeds each
Seeds/pod could range between 1 and up to 20
in very rare cases.
Length of pods depends on seed number
present
Yardlong bean (V. sesquipedalis) can reach up
to 1 meter and more in length
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Grain is the most economically important
part of cowpea
Grain yield depends on:
Number of seeds that mature
Cultivar performance
Environment
Plant population density
Stress caused by biotic factors
Nitrogen source
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Grain yield adversely affected by
drought and high night temperature
Insect pests
Aphid at seedling
Flower thrips at flowering
Maruca at podding
Pod sucking bugs at pod filling
Bruchid on stored seed/grain