ACHARYA N.G.RANGA AGRICULTURAL UNIVERSITY

DEPARTMENT OF AGRONOMY

112/28/15

Presented by:KANCHETI MRUNALINI

Physiology of grain yield in cereals

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In cereals, grain filling is largely dependent on photosynthesis and

environmental conditions after flowering, but the capacity for

storage is determined by conditions before flowering – have

dominant influence on yield.(Japanese IBP experiments on Rice P-

90).

In wheat, varieties in which the photosynthetic rate of flag leaves

under controlled environmental conditions falls substantially

during the period between end of stem growth and beginning of

grain growth, but rises again as export of assimilate to the grain

increases.

Seasonal sequence of condition plays a major role in determining

whether source/ sink is more limiting.

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In crop production point of view solar energy is to be

conserved for future use via its fixation is biomass by the

process of photosynthesis.

In this process, CO2 from the air is converted into

carbohydrates.

This Process is called CO2 assimilation.

6CO2 + 6H2O C6H12O6 + 6O2

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About 40% of weight of carbohydrates formed during assimilation process is lost by Respiration.Substraction of the rate respiration from the assimilation rates gives the rates of increase in plant dry weight

Part of the carbohydrates produced is used as building material

for structural plant drymatter as cellulose proteins lignin and

fats and a part of this as photosynthates used as a source of energy

for plant process.

The release of energy from carbohydrates produced during

assimilation process is described by the following equation.

C6H12O6 + 6O2 6CO2 + 6H2O + energy

This process is called respiration.12/28/15 5

Sigmoid curve of growth Sigmoid curve of growth raterate

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With respect to the growth rate 3 phase may be distribution :

During the first phase crop consists of individual plants that do not shade each other and crop growth rate, increases.

In the second phase crop covers soil completely and crop growth is constant .

In the 3rd phase crop is matured and crop growth rate is decreased .

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In the first phase major part of assimilates are invested in the leaf growth. This growth in leaf area is accompanied by a proportional increase in energy interception because neighbouring plants are so small that mutual shading hardly place a role.

Individual plant weight increases by constant proportion per day thus leading to exponential growth .

After a closed surface has been formed more leaf growth does not lead more light interception, hence the CG remains constant and total plant increase linearly.

In the last phase leaf senescence leads to decrease in the CG

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Major part of total drymatter accumulation is achieved during the second phase.

Total drymatter production of crop has largely determined by magnitude of CGR during linear phase and duration of the phase.

The duration of period of linear growth is superior and cultivar specific and more over is influenced by environmental conditions.

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Like solar radiation and temperature , supply of nutrients and water , occurance of weeds, pests and diseases , with an optimum supply of water and nutrients in absence of weeds, pests and diseases, the growth rate is determined by solar radiation and temperature and this is referred to as Potential Growth Rate.

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Assimilation in C3 and C4 cropsAssimilation in C3 and C4 cropsPhotosynthetic advantage of C4 compared with

plants at levels of carboxylation is attenuated at the whole leaf by combination of stomatal and mesophyll resistances and still more so at the level of crop photosynthesis by shading, periods of low light and respiration with the result that no consistent advantage of C4 pathway is evident in maximum crop growth rates and yields

.The real value of C4 pathway probably lies elsewhere

in its better adoption to high temperature –high insolation condition provided the nights are not cold, just as C3 plants perform better under cool conditions with only moderate insolation. 12/28/15 11

COCO22 assimilation of a single assimilation of a single leafleaf

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Maximum rate of net CO2 assimilation at high light intensity (Fm)

C4- plants – 30-90 kg / ha /hrC3-plants- 15-50 kg / ha /hrGrowth rate of respiration (Fg) is the sum of net

rate and the concurrent dark respiration.The dark respiration is at normal temperatures

roughly 1/9th of the maximum net assimilation rate .

Maximum net assimilation rate and dark respiration are much more effected by temperature than the initial light use efficiency.

Under field conditions , where plants are subjected to fluctuating temperature conditions, there appears to be adoption of the photosynthetic apparatus. 12/28/15 13

Canopy COCanopy CO22 assimilation assimilation For crop photosynthesis, relative advantage of C4 over C3 plants is

less than at the level of single leaf due shading of lower leaves and to increasing importance of aerodynamic compared with the leaf resistance to CO2 exchange(Slatyr, 1970)

Highest rates of photosynthesis measured on wheat crops (Denmead, 1970) by aerodynamic methods are only slightly less than those for maize.(Lemon, 1967)

If the crop is of C3 type LAI of one Assimilation rate is of 25 kg /ha /hr actual leaf area Ground areaFor an LAI of 4, CO2 assimilation rate is about 39 kg/ ha /hr12/28/15 14

Dry matter Dry matter AccumulationAccumulation

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Increasing light intensity and photosynthesis, increases demand for assimilates. (King et. al.,) can lead to increase in rate of assimilate export from leaves .

In rice grain filling is slow during low temperatures because of slow rate of translocation.(Murata and Matsushima)

Higher rates of mass transfer per unit phloem area is studied in Soybean petioles (Fisher, 1970) in leaves of C4 , grasses (Lush and Evans, 1978) and wheat roots (Passiouva, 1974)

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PartitioningPartitioning ofof AssimilatesAssimilates Pattern of assimilate distribution determined by rate

of photosynthesis, strength and proximities of various sink environmental conditions.

In sugarbeet, for eg., a limiting supply of photosynthates to leaves and more to roots instead under water stress.

Rice – flagleaf and penultimate leaves are main suppliers to ear.

(King et.al., )Pea, soybean, auxillary inflorescence supported by

subtending leaf. (Wardlaw, 1968)Cotton boll - younger leaf is responsible for yield.Root crops- uppermost leaves responsible.Older tobacco leaves preferentially support

younger ones 3, 5, 8 nodes above them. (Jones et.al., 1959)

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GROWTH AND MAINTENANCE RESPIRATION

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RESPIRATION

Oxidation of organic substances to CO2

and water

Can be divided into 3 groups :

Autotrophic respiration / plant

respiration.

Heterotrophic respiration / soil

respiration.

Photorespiration.

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AUTOTROPHIC RESPIRATION

o Capable of self-nourishment

o Requires only minerals for growth

o Uses carbonate or carbon dioxide as a source of

carbon and simple inorganic nitrogen as a

nitrogen source

Common chemical equation of autotrophic respiration for glucose is:

C6H12O6 + 6O2 6CO2 + 6H2O + energy12/28/15 20

The autotrophic respiration consists of:

•Growth Respiration

•Maintenance Respiration12/28/15 21

Diagram 2: Example of Autotrophic Respiration of plant12/28/15 22

GROWTH RESPIRATION

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Represents metabolic cost of converting the translocated

products of photosynthesis to structure,cytoplasmic/

storage .

The conversion of primary photosynthesis into structural plant

material as cellulase, proteins , lignin and fats requires and

energy for synthesis of end product , the transport of sugars

and the uptake of nitrogen and minerals.12/28/15 24

Therfore, part of the sugars assimilated is respired to

provide energy for the synthesis of new plant

components.

At higher temperature,rate of conversion of primary

photosynthates into structural plantmaterial changes but

the conversion efficiency remains constant, because the

biochemical pathway is not effected by temperature.

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MAINTIANANCE

RESPIRATION

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Maintenance respiration of crops towards end of their

life cycle, but it would be satisfactorily to base its

estimation as accordingly of non-storage protein and

membrane components which turns over for more

rapidly than all wall constituents and storage

polysaccharides, proteins and oils.

Proteins in the plant , especially in the leaves consist

mainly of enzymes which have only a limited life

span .

They deteriorate about 0.1% a day at a temperature

of 20 0

C and have to be resynthesized .

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Temperature is the most important environmental factor

affecting maintenance respiration

The metabolic costs of the repair of injury from stress

(biotic/abiotic) also considered as part of maintenance

respiration

Essential for biological health and growth of plants, sustain

living tissues.

Maintenance respiration is a key component of most

physiologically based mathematical models of plant growth,

including models of crop growth and yield and models of

ecosystem primary production and carbon balance.

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Maintenance versus growth respiration:

Growth respiration can be distinguished from maintenance respiration

by relating variation in respiration rate to variation in RGR over short

time intervals .

This approach assumes a model for respiration where:

{Total respiration} = {Maintenance respiration} + {(Specific costs of

growth} * {RGR)} ]

where respiration is expressed in mmol CO2 g-1

 d-1

, and specific costs

of growth in mmol CO2 g-1

.

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Than

k you

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