Morphology and Physiology of Soybean

A member of CGIAR consortium www.iita.org
MORPHOLOGY AND PHYSIOLOGY OF
SOYBEAN
Baffour Asafo-Adjei
IITA, Ibadan
July 28, 2015

OUTLINE
• Introduction
• Botany and structure of soybean plant
• Growth stages of soybean plant
• Growth and development

INTRODUCTION
• Importance
Why is soybean important?
• Geographic Distribution
How widely is it produced?

INTRODUCTION
Importance
• Soybean is the most important grain legume in the world in
terms of production and use.
• It is important in Africa and Nigeria for three key reasons.
- Employment and incomes to people (farmers,
processors, marketers)
- Nutrition and health benefits
- Role in sustainable farming systems (N2 organic
carbon, cereal striga management)

INTRODUCTION contd.
2012 Soybean production (FAO 2015)
Region/Country Area (Ha) Yield
(Kg/Ha)
Production
(Tonnes)
World 105,018,859 2,295 240,971,130
Africa 1,776,591 1,179 2,094,382
W. Africa 723,748 963 696,705
Nigeria 668,300 973 650,000
Ghana ? ? ?

INTRODUCTION contd.
Geographic Distribution
 Currently grown in various environments throughout the
world.
 Extensively cultivated in tropical Brazil; sub-tropical
Central America and Southern USA; temperate Northern
USA and Canada, and sub-arctic Sweden and Siberia
 Introduction of soybean in most African countries is very
recent (mostly in the 20th century).

BOTANY AND STRUCTURE OF SOYBEAN PLANT
Botany
• Cultivated soybean (Glycin max) is an annual crop.
• It belongs to the family Leguminosae
• Sub - family Papilionoideae and tribe Phaseolae.
• It is a diploid with chromosome number 2n=2x=40.
• Some of the wild and semi-wild relatives e.g.
G. falcata and G. latifolia are also diploid
• Others such as G. tabacina and G. tomentella are tetraploids
(2n = 4x = 80).

BOTANY AND STRUCTURE OF SOYBEAN PLANT contd.
Botany
• Some of the wild species may have genes controlling useful
traits that may be lacking in the cultivated specie
• It has not been easy to transfer such traits Into cultivated
soybean due to the difficulty in obtaining fertile/viable seed
from Inter- specific hybridization.

Structure of soybean
plant
• Cultivated soybean is
generally an erect,
sparsely branched bush
type – unlike the
spreading sometimes
vinery characteristics of
wild and semi-wild
species

Structure of soybean plant
• There are two types of stem growth habit and floral
initiation in soybean.
• These are the determinate and indeterminate types.
• Most of the varieties cultivated in the tropics are
determinate while those in the temperate regions are
indeterminate

Determinate
• Vegetative growth of terminal bud
ceases when it becomes an
inflorescence.
• Flowering occurs about the same
time along the length of the plant,
hence pod and seed development
and maturation occur uniformly
throughout the plant.
• Terminal leaves are of the same size
as those at the bottom of the main
stem.
Indeterminate
• Plant may have achieved less than
half its final height when it starts
flowering.
• Plant continues to grow taller while
flowering also continue.
• Flowering/pod and seed
development are spread over a
longer period
• Pod and seed development on lower
parts of the plant are more
advanced than those at the top.
• They do not have terminal
inflorescence.
• Terminal leaves are smaller than
those which are lower on the plant

Root
• Consists of a taproot that may go deep
into the soil depending on cultural
conditions
• The root system is usually in the top 30-
60 cm of soil with about 80-90 of dry
weight occurring in the top 15 cm of the
soil.
• Nodules may be visible 10 days after
planting if the appropriate rhizobia are
present in the soil.
Stem
• Well-developed main stem, may have 0-6
lateral branches and grow to a height of
20 cm to over 100 cm depending on
variety and cultural/environmental
conditions
Structure of soybean plant

Leaves
• Two main types: Primary and
Trifoliate leaves.
• The primary leaves are ovate with 1-
2 cm length petioles and a pair of
stipules at its point of attachment to
the stem
• The trifoliate leaves are alternate
and have long petioles. Leaflets have
entire margins and are broadly ovate
to elliptic-Ianceolate in shape
Primary and Trifoliate leaves

Inflorescence
• Soybean has a typical papilionaceous
flower.
• It consists of a tabular calyx with five
sepal lobes; a corolla made up of a
standard petal, two lateral wing
petals, and two anterior keel petals.
• Nine of the ten stamens are fused
leaving the posterior one separate
• The pistil is made of an ovary that
contains 1-5 ovules, a style that
accrues towards the standard and a
capitate stigma.
• Pollination occurs before the flower
opens
Soybean flowers

Pod
• Pods are borne in clusters on short
stalks, pubescent and of varied
colours depending on cultivar. They
may be straight or slightly curved,
about 1 cm in width and 3-7 cm long
when matured
Seeds
• Matured soybean seed may be
spherical in shape or may be
flattened and elongated to various
degrees depending on variety
• Seed size may range from 5 - 40 g
per 100 seeds with most varieties
between 10 and 20 g per 100 seeds

GROWTH STAGES

DESCRIPTION OF VEGETATIVE STAGES
Stage Stage Title Description
VE Emergence Cotyledon above soil surface
VC Cotyledon Unifoliate leaves unrolled sufficiently
so that leaf edges are not touching
V1 First -node Fully developed leaves at unifoliate
node
V2 Second-node Fully developed trifoliate leaf at node
above the unifoliate
V3 Third-node Three nodes on main stem with fully
developed leaves beginning with the
unifoliate node
V(n) nth.-node n number of nodes on main stem with
fully developed leaves beginning with
the unifoliate

DESCRIPTION OF REPRODUCTIVE STAGES
Stage Stage
Title
Description
R1 Beginning
bloom
One open flower at any node on main stem
R2 Full
bloom
Open flower at one of the two uppermost
nodes on main stem with a fully developed
leaf
R3 Beginning
pod
Pods 5 mm long at one of the four uppermost
nodes on main stem with fully developed
leaf
R4 Full pod Pods 2 cm long at one of the four uppermost
nodes on main stem with fully developed
leaf

Stage Stage
Title
Description
R5 Beginning
seed
Seeds 3 mm long in a pod at one of the four
uppermost nodes on main stem with fully
developed leaf
R6 Full seed Pod containing a green seed that fills the pod
cavity at one of the four uppermost nodes on
main stem with fully developed leaf
R7 Beginning
maturity
One normal pod on main stem that has
reached its mature pod colour
R8 Full
maturity*
95% of pods have reached their matured pod
colour
* 5-10days of dry weather are required after R8 for seeds to have <15% moisture content

V2
• Fully developed
trifoliate leaf at node
above the unifoliate

V5
• Five nodes on main
stem with fully
developed leaves
beginning with the
unifoliate

R1
• One open flower at any
node on main stem

R2
• Open flower at one of
the two uppermost
nodes on main stem
with a fully developed
leaf

R3
• Pods 5 mm long at one
of the four uppermost
nodes on main stem
with fully developed
leaf

R4
• Pods 2 cm long at one
of the four uppermost
nodes on main stem
with fully developed
leaf

R5
• Seeds 3 mm long in a
pod at one of the four
uppermost nodes on
main stem with fully
developed leaf

R6
Pod containing a green
seed that fills the pod
cavity at one of the four
uppermost nodes on
main stem with fully
developed leaf

R7
• One normal pod on
main stem that has
reached its mature pod
colour

R8
• 95% of pods have
reached their matured
pod colour

GROWTH AND DEVELOPMENT

Growth:
May be defined as a gain in
dry matter production.
It is affected by two main
factors.
• Genetic or Internal factors,
and
• Environmental or external
factors

Genetic or Internal factors
• Resistance tolerance to biotic (e.g. diseases/insects), and abiotic (e.g.
heat/shade and soil pH/ nutrient toxicity).
• Enzyme activity
• Rate and type of various biochemical reactions (e.g. photosynthesis,
respiration, partitioning of assimilates)
• Cell differentiation
etc

Genetic or Internal factors
Breeding for resistance /tolerance
to biotic & abiotic stresses are major
breeding objectives of most
soybean programs – cost effective /
efficient, sustainable &
environmentally friendly.

Environmental or external factors
• Biological: Diseases, Insects, weeds and soil micro-
organisms (e.g. Nitrogen fixing bacteria, denitrifying
bacteria mycorrhiza)
• Climatic: Light, temperature, water, day length, gases (C02, O2, SO2, Cl
etc.)
• Soil: Texture, structure, organic matter content, CEC, pH, Nutrient
availability

IMPORTANT FACTORS THAT AFFECT SOYBEAN GROWTH AND
DEVELOPMENT
Light
• The effect of light on plant growth is expressed primarily through
photosynthesis and other related processes.
• Reduced radiation reduces photosynthetic rates and consequently dry
matter accumulation
• In a soybean field, leaves near the surface of the canopy intercept more
light than lower leaves. Vertical leaf orientation is also known to
enhance light interception when leaf area index (LA I) is greater than 3.0.
• Varieties with vertical leaf orientation would thus be expected to be
more productive because light interception is improved and
photosynthetic activity is also increased.
Breeding implications?

DEVELOPMENT
Temperature
• Plant growth depends on several biochemical processes taking place in the plant.
The rates at which these processes take place are influenced by temperature.
• Different biochemical processes require different optimum temperature e.g. the
optimum rate of photosynthesis in Individual soybean leaves is achieved at about
35°C to 40°C. Respiration however continues to increase above these
temperatures. On the other hand the optimum temperature for dry matter
accumulation is about 30°C.
• Effect of temperature depends also on the stage of crop development.
Seed germinates between 10°C -40°C however, low soil temperature at planting
results in low germination and seedling development.
Seed developed in hot weather ( > 33°C) tend to have poor germination, while
seed viability deteriorates rapidly when stored in warm temperature ( >30°C)
conditions.

DEVELOPMENT
Temperature
• Vegetative growth is affected by both soil and air temperatures. Soil
temperatures of about 22°C - 27°C are considered the most favourable
for soybean root growth
• Flowering pod and seed development: Flowering is poor below 200 C and
increases up to about 320C beyond which flower abortion results.
• Generally high temperature and excessive heat tend to increase flower
and pod abortion

DEVELOPMENT
Photoperiod
• Soybean is naturally a short day plant but cultivars differ in critical day-
length requirements.
• Photoperiod affects plant height and the number of nodes produced.
Both characters increase with increasing day length
• Thus, cultivars adapted to the long-day (14-16hrs) summer conditions in
the temperate regions will be shorter, have fewer nodes, flower earlier
and will produce less dry matter when planted in tropical environment
(shorter day lengths 12 hrs.).
• Conversely, cultivars adapted to the tropics when planted in temperate
environments, grow taller, produce more nodes and flowering is delayed
until the day length shortens

DEVELOPMENT
Moisture
• Soybean will experience water stress when there is either excess
moisture in the soil or there is a deficit in available soil moisture.
• Excess soil moisture injures root system by reducing aeration, and soil
moisture deficit results in dehydration of the shoot.
• Soybean requires about 580g of water per gram of dry matter produced
• For soybean seed to germinate, it has to imbibe about 500g I kg of dry
weight. Thus both low soil moisture content and excessive soil moisture
will result in poor germination

DEVELOPMENT
Soil
The physical, chemical and biological properties of the soil affect plant
growth and development. Soybean requires a well-drained loamy soil for
proper growth
• Heavy soils impede seed emergence, resulting in poor stands root
development is also restricted. Light or loamy soils however encourage
good root development
• Sandy soils low in organic matter, have low moisture holding capacity
and plants growing on such soils tend to experience drought stress.
Soybean requires the 16 essential elements for its growth and development.
Absence or non-availability of any of these elements results in abnormal
or sub-normal plant growth. Plants show characteristic nutrient
deficiency symptoms.

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Morphology and Physiology of Soybean

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