morphology and physiology of soybean

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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 DistributionHow 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


DESCRIPTION OF REPRODUCTIVE STAGES

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


DESCRIPTION OF REPRODUCTIVE STAGES

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



R6Pod 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 indry 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?



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.



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



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



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



SoilThe 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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