The document discusses physiology of grain yield in cereals. It notes that grain filling is dependent on photosynthesis and environmental conditions after flowering, while storage capacity is determined by pre-flowering conditions. It also discusses that the photosynthetic rate of wheat flag leaves falls and rises during grain growth. The document covers topics like photosynthesis, respiration, dry matter accumulation, growth rates, and partitioning of assimilates in different crops. It distinguishes between C3 and C4 photosynthesis pathways and their assimilation rates. It also describes the different types of respiration in plants like growth, maintenance, and their relationship to temperature.

1. ACHARYA N.G.RANGA AGRICULTURAL
UNIVERSITY
DEPARTMENT OF AGRONOMY
112/28/15
Presented by:
KANCHETI MRUNALINI

2. Physiology of grain yield in cereals
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3. 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.
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4. 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.
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5. 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.
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6. Sigmoid curve of growth rateSigmoid curve of growth rate
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7.  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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8.  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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9.  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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10.  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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11. Assimilation in C3 and C4 cropsAssimilation in C3 and C4 crops
 Photosynthetic 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.
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12. COCO22 assimilation of a single leafassimilation of a single leaf
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13.  Maximum rate of net CO2 assimilation at high light intensity
(Fm)
 C4- plants – 30-90 kg / ha /hr
 C3-plants- 15-50 kg / ha /hr
 Growth 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.
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14. Canopy COCanopy CO22 assimilationassimilation
 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 area
For an LAI of 4, CO2 assimilation rate is about 39 kg/ ha /hr12/28/15 14

15. Dry matter AccumulationDry matter Accumulation
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16. 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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17. 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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18. GROWTH
AND
MAINTENANCE
RESPIRATION
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19. RESPIRATIONRESPIRATION
 Oxidation of organic substances to CO2 and water
Can be divided into 3 groups :
 Autotrophic respiration / plant respiration.
 Heterotrophic respiration / soil respiration.
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20. 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

21. The autotrophic respiration consists of:
•Growth Respiration
•Maintenance Respiration12/28/15 21

22. Diagram 2: Example of Autotrophic Respiration of plant
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23. GROWTH
RESPIRATION
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24.  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.
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25.  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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26. MAINTIANANCE
RESPIRATION
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27.  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 .12/28/15 27

28.  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.
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29. 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)} ]
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30. 12/28/15 30

31. Thank
you
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