Agro-physiological basis of variation in yield

1. Agro-physiological
basis of variation in
yield
By Pragya Tiwari
PhD. Agronomy

2. WHAT IS PHYSIOLOGY?
Physiology: Physiology is the study of functional aspects of crop plants.
Crop physiology: Crop physiology is concerned with the processes and functions of
the crops at cellular, sub-cellular and whole plant levels in response to environmental
variables and growth.

3. PHYSIOLOGY OF CROP
Cell: A cell is the smallest unit of life. Cells are often called the "building blocks of
life". The study of cells is called cell biology. Cells consist of cytoplasm enclosed
within a membrane, which contains many biomolecules such as proteins and nucleic
acids. Cell contain a nucleus, a cytoplasm, and sub cellular organelles, and they are
enclosed in a membrane that defines their boundaries
Cell wall: A rigid layer of polysaccharides lying outside the plasma membrane of the
cells of plants, fungi, and bacteria. In the algae and higher plants it consists mainly of
cellulose.
Primary cell wall: The primary cell wall is the part or layer of cell wall in
which cell growth is permitted. Compared to secondary cell wall, this layer contains
more pectin and lignin is absent until a secondary wall has formed on top of it.
Compare: secondary cell wall, middle lamella.
Secondary cell wall: The secondary cell wall is a structure found in many plant cells,
located between the primary cell wall and the plasma membrane. The cell starts
producing the secondary cell wall after the primary cell wall is complete and
the cell has stopped expanding. Secondary cell walls owe their strength and toughness
to lignin, a brittle, glue-like material

4. Middle lamella: The middle lamella is a pectin layer which cements the cell
walls of two adjoining plant cells together. It is the first formed layer which is
deposited at the time of cytokinesis. The cell plate that is formed during cell
division itself develops into middle lamella or lamellum.
Cell membrane: The semipermeable membrane surrounding the cytoplasm of a cell.
Also known as plasma membrane.
Semipermeable: A material or membrane allowing certain substances to pass through it
but not others, especially allowing the passage of a solvent but not of certain solutes.
Cytoplasm: The material or protoplasm within a living cell, excluding the nucleus.

5. Cell organelles: Eukaryotic cells contain a membrane-bound nucleus
and numerous membrane-enclosed organelles (e.g., mitochondria,
lysosomes, Golgi apparatus) not found in prokaryotes. The nucleus
contains most of the genetic material (DNA) of the cell. Additional
DNA is in the mitochondria and (if present) chloroplasts

6. Agro-physiological basis of variation in yield
Plant production is driven by photosynthesis. Key elements in the system are:
1) The interception of photosynthetically active radiation (PAR, 400-700 nm spectral
band).

8. 2) Use of that energy in the reduction of CO2 and other substrates
(photosynthesis).

9. 3) Incorporation of assimilates into new plant structures (biosynthesis and growth),
4) Maintenance of plant as living unit.

14. Source and Sink
• It is widely believed that yield gains are most likely to be achieved by
simultaneously increasing both source (photosynthetic rate) and sink
(partitioning to grain) strengths.
• Fischer (1975, 1985) established critical nature of the rapid spike-
growth phase in determining yield.
• Duration of rapid spike growth has been successfully manipulated
using photoperiod, revealing a strong relationship between its duration
and number of fertile florets/spike (Miralles and Richards, 1999).
• By maintaining plants at a relatively short photoperiod during this
growth phase, number of days from terminal spikelet to heading was
increased from 50 to 70 d, with 13- and 9-h photoperiods,
respectively, while number of fertile florets per spike increased from
77 to 108.

21. Plant ideotypes
The production of every plant is affected by the plant’s type, climatic condition, soil type
and management factors. The production of the plant might be increased by changing plant
type and increasing the period of grain filling in a certain climatic conditions where
management and soil factors are not limited.
There is a direct relationship between the plant’s type and crop yield because the
orientation and number of leaves play an important role in carbon fixation
(photosynthesis). In recent years due to all round efforts of agricultural scientists, it has
been possible to cultivate HYVs of cereal crops which are often been termed as “NEW
PLANT TYPES”. ( NPT)
IDEOTYPE: refers to plant type in which morphological and physiological characteristics
are ideally suited to achieve high production potential and yield reliability. The concept of
ideotype was given by Donald in 1968. He illustrated that there should be minimum
competition between the crops and crop must be competent to compete with weeds.

22. Important features of such NPT’s of cereals in grain crops are:
• DWARFNESS:
• EFFICIANT LEAF ARRANGEMENT:
• SYNCHRONOUS TILLERING:
• LOW FLORET STERILITY:
• SHORTER GROWTH DURATION:
• ADAPTABILITY TO DIFFERENT CROP SEASONS:
• ABSENCE OF SEED DORMANCY:
• EFFECTIVE TRANSLOCATION OF FOOD MATERIAL FROM PLANTS
TO GRAIN
RESPONSIVE TO HEAVY FERTILISER APPLICATIONS:
LODGINIG RESISTANCE:
YIELDING POTENTIALITY:
PESTS RESISTANCE

23. Ideotypes for some crops/situation
Wheat
According to Donald (1968), the ideotype for wheat crop has following features-
1.Short strong stem to avoid lodging.
2.Flat leaves parallel to soil
3. Few small erect leaves to allow the sunshine into its canopy.
4. Strong and deep root system.
5.A large erect ear.
6. More number of fertile florets per unit area therefore more harvest index.
7. Presence of awns to increase the photosynthesis area.
8. A single culm to avoid wasteful vegetative growth.
9. A grain development period coinciding with mean max temperature of
25 oC
10. Resistance to insect-pest and diseases.
11. Proper partitioning and translocation of assimilates.

24. Wheat:- in 1968 Donald proposed ideal plant
type of wheat.
Features:
 Short strong stem.
 Erect leaves.
 Few small leaves.
 Large Ear.
 Erect Ear.
 Single culm.
 Presence of awns.

25. Ideotypes for some crops/situation
Rice
1. Short growth duration (85-100 days).
2. Effective deep root system.
3. Dwarf plant (<110 cm) with erect leaves and thick stem.
4. Early strong fertile tillering.
5. Synchronized flowering.
6. Good number of panicles (about 400/m2).
7. Higher number of grains per panicle.
8. Moderate seed dormancy.

26. Rice:- in 1964, Jennings introduced ideal plant of rice
Features:
 Erect, short and thick leaves.
 Semi-dwarf stature.
 High tillering capacity.
 More panicles.
 High harvest index.
 Greater culm diameter.
 Lower relative internodes
elongation.

27. Maize :- in 1975, Mock and Pearce proposed Ideal Plant
type of maize .
Features:
 Small tassel size.
 Low tillers.
 Large cobs
 Angled leaves for good light
interception.
 cold tolerance and developing
 seedling.
 Maximum photosynthetic
efficiency.

28. Maize
The plants have erect upper leaves and the lower leaves
gradually become horizontal to allow the sunshine into its
canopy and for proper movement of air into the field. The
height of the plant is to be 1.5 m in which cobs may be
produced on the nodes near the tassel.
Resistance to insect-pest and diseases.

29. STRESS

34.  DROUGHT-A drought is a natural phenomenon of below-average precipitation
in a given region, resulting in prolonged shortages in the water supply, whether
atmospheric, surface water or ground water.
 Drought is defined as the deficiency of water severe enough to check the plant
growth.
 Atmospheric drought occurs due to low atmospheric humidity, high wind velocity
and high temperature which cause a plant to lose most of its water.

35. PHYSIOLOGICAL EFFECT OF DROUGHT IN PLANTS
 Functioning of stomata
 Carbohydrates metabolism in green leaves
 Photosynthetic activity
 Osmotic pressure
 Biochemical effects
Morphological changes due to Drought:
•Reproductive growth
i. In relation to Ontogeny: Generally, the life-cycle of the annual crops
is conveniently divided into three distinct phases as:
• Seed germination and seedling development
• Vegetative growth
• Seed germination and Seedling growth: Under field conditions,
seed germination and seedling growth are inhibited by the water stress
in the soil resulting in the poor stands of the crop.

36. ii. Vegetative growth: Vegetative growth and leaf expansion, in
particular is severely inhibited by the soil water deficit. Visible injury is
seen in the form of wilting. Paleness and dryness of leaves is seen in the
drought. Leaf abscission is often noticed due to the accumulation of ABA
under drought. Reduced growth is also due to reduction in cell volume
and water potential.
iii. Reproductive growth: Reproductive phase of the crop is highly
sensitive to water stress,an imbalance between light capture and its
utilization, which inhibits the Drought creates photosynthesis in leaves.
In this process imbalance between the generation and utilization of
electrons is created

38. Effect drought stress on plants metabolic activities:
Reduction of turgor pressure, due to cell size will be smaller.
Effect on photosynthesis: Photosynthesis decreases due to distruption
of PS II (photo system II), stomatal closure and decrease in electron
transport.
Decrease in nuclear acid and proteins Protease activity, RNA
hydrolysis and DNA content falls down.
Effect on Nitrogen metabolism. Nitrate reductase activity, nitrite
reductase activity insensitive.
Effect on carbohydrate metabolism; Loss of starch and carbohydrate
translocation decrease.

41. . Effect on Cereals: Water deficit during initiation of floral primordial and
anthesis is injurious to cereals like rice and wheat. Loss of flowering
synchrony is detrimental to the crop yield. Stress during ripening stage
results in reduction in the test weight in cereals.
•Affect plant height and leaf area
•Leaf weight was significantly reduced.
•Reduced photosynthesis.
•The total dry matter decreased significantly
•Reduced stomatal conductance
•Leaf rolling drying and premature leaf death

42. WHAT IS CHILLING INJURY?
 Plant chilling injury refers to an injury that is caused by a temperature drop to below
to 10 to 15°C but above the freezing point.
 Among crops, maize, Phaseolus bean, rice, tomato, cucumber, sweet potato, and
cotton are chilling sensitive.
 The most common site implicated for chilling injury is the plasma membrane.
 The consequences of this change may lead to cell leakage or disruption.
 Changes in membrane permeability are often invoked as a cause of the loss of cell
turgidity.

44.  EFFECT OF CHILLING INJURY
 Cellular changes: Changes in membrane structure and composition, decreased protoplasmic
streaming, electrolyte leakage and plasmolysis.
 Altered metabolism : Increased or reduced respiration, depending on severity of stress,
production of abnormal metabolites due to anaerobic condition.
 Common Symptoms
• – Reduced plant growth and death
• – Surface lesions on leaves and fruits
• – Abnormal curling, lobbing and crinkling of leaves

45. • – Water soaking of tissues
• – Cracking, splitting and dieback of stems
• – Internal discolouration (vascular browning)
• – Increased susceptibility to decay
• – Failure to ripen normally
• – Loss of vigour (potato lose the ability to sprout if chilled)

47.  Chilling injury causes several metabolic or physiological dysfunctions to the plant
including
 Disruption of the conversion of starch to sugars.
 Decreased carbon dioxide exchange
 Reduction in net photosynthesis
 The destruction/degradation of chlorophyll

48. Salinity
The term ‘salinity’ refers to the presence of salt in soil and water of electrolytic mineral
solutes in concentrations that are harmful to many agricultural crops.
SALT STRESS
• “Plant salt stress is a condition where excessive salts in soil solution cause
inhibition of plant growth or plant death. On a world scale, no toxic substance
restricts plant growth more than does salt.”
• Salt’s negative effects on plant growth have initially been associated with the
osmotic stress component caused by decreases in soil water potential and,
consequently, restriction of water uptake by roots.
• It is estimated that about one-third of the irrigated land on earth is affected by
salt.

49. Physiological effect of salt stress on crop growth
.Osmotic stress
.Water stress
.Ion toxicity
.Nutritional disorders
.Oxidative stress
.Alteration of metabolic processes
.Membrane disorganization
.Reduction of cell division and expansion

51. Physiological effects on plants
On growth
• Decreased rate of leaf growth after an increase in soil salinity
is primarily due to the osmotic effect of the salt around the
roots.
• Increase in soil salinity causes leaf cells to loose water.
• Reductions in cell elongation and also cell division lead to
slower leaf appearance and smaller final size

52. Oxidative stress
• Due to increase in salinity stress, photosynthetic rate decreases which
increases the formation of reactive oxygen species (ROS), and increases
the activity of enzymes that detoxify these species.
• Plants undergo adjustments in leaf morphology, chloroplast pigment
composition, and in the activity of biochemical processes that prevent
oxidative damage to photosystems.
• This maintains H2O2 at levels required for cell signalling

53. Seed germination
Seed germination in saline condition is affected by three ways.
. Increased osmotic pressure ofthe soil solution which restricts
the absorption and entry of water into the seeds.
. Certain salt constituents are toxic to the embryo and
seedlings. Anions like NO32-
, Cl-
SO4-2 are more harmful to
seed germination.
. Salt stress hampers the metabolism of stored materials

54. Vegetative growth
• During vegetative stage, salt induced water stress causes
closure of stomata leads to reduction in CO2 assimilation
and transpiration.
• Reduced turgor potential affects the leaf expansion.
• Because of reduction in leaf area, light interception is
reduced, photosynthetic rate is affected which coupled with
spurt in respiration, resulting into reduced biomass
accumulation.

56. Photosynthesis
• Accumulation of high concentration of Na+ and Cl- in chloroplast, photosynthesis
is inhibited.
• Since photosynthetic electron transport appears relatively insensitive to salts, either
carbon metabolism or photophosphorylation may be affected.
• Photosynthetic enzyme or the enzymes responsible for carbon assimilation are
very sensitive to the presence of NaCl.
• The key enzyme, nitrate reductase is very sensitive to NaCl .
Nitrogen metabolism
• One of the amino acids, glycinebetaine shows increased trend with increase in
salinity in perennial halophytes and Atriplexspecies.
• Proline is an α amino acid, accumulates in large amounts as compared to
all other amino acids in salt stressed plants.

57. 57
• Growth analysis can be used to account for growth
in terms that have functional or structural
significance.
• The type of growth analysis requires measurement
of plant biomass and leaf area and methods of
computing certain parameters that describe growth.
GROWTH ANALYSIS

58. 58
Leaf Area
 This is the area of photosynthetic surface
produced by the individual plant over a period of
interval of time and expressed in cm-2 plant-1.
 Efficient crop species tend to invest most of their
early growth in expansion of leaf area, which results
in efficient use of solar radiation.

59. CROP GROWTH RATE(CGR)
This concept was 1st described by Watson in 1952.
The crop growth rate simply indicates the change in
dry matter accumulation over a period of time.
This expression can be used without any assumption
about the form of the growth curve.
The formulae can be used to compare treatments
between and within experiments. They can even been
used when it is possible to make only two harvests.

60. Formula of CGR
CGR= (W2-W1)
(t2-t1) x P
Where:
t 1 = time one ( in days)
t 2 =time two(in days)
W1 = Dry weight of plant at time one ( in grams)
W2 = Dry weight of plant at time ( in grams)
P = Unit area
Unit : g/m2 /unit time(day)

61. Formula of CGR
CGR= (W2-W1)
(t2-t1) x P
Where:
t 1 = time one ( in days)
t 2 =time two(in days)
W1 = Dry weight of plant at time one ( in grams)
W2 = Dry weight of plant at time ( in grams)
P = Unit area
Unit : g/m-2 /unit time(day)

62. RELATIVE GROWTH RATE(RGR)
 This concept was 1st given by Blackman in 1919.
 Crop growth rate is a measure of the increase in size,
mass or number of crops over a period of time.
 The increase can be plotted as a logarithmic or
exponential curve in many cases.
 Relative growth rate is the slope of a curve that
represents logarithmic growth over a period of time.
 An exponential growth rate is not sustainable over
time. The curve typically flattens out, representing
saturation in a growth at a certain point of time .

63. Formula:
RGR= (ln W2 – ln W1 )
(t2-t1)
Where:
In=natural logarithm
t 1 = time one ( in days)
t 2 =time two(in days)
W1 = Dry weight of plant at time one ( in grams)
W2 = Dry weight of plant at time (in grams)
Unit: g/g/day

64. Leaf Area Index (LAI)
Williams (1946) proposed the term, Leaf Area Index (LAI).
It is the ratio of the leaf of the crop to the ground area over a period
of interval of time.
The value of LAI should be optimum at the maximum ground
cover area at which crop canopy receives maximum solar radiation
and hence, the TDMA will be high.
A LAI of 3-5 is usually necessary for maximum dry matter
production of most cultivated crops.
64
64
LAI =
Total leaf area of a
plant
Ground area occupied by the plant

65. 65
Leaf Area Ratio (LAR)
 The term, Leaf Area Ratio was suggested by Radford (1967)
 LAR expresses the ratio between the area of leaf lamina to the
total plant biomass or the LAR reflects the leafiness of a plant or
amount of leaf area formed per unit of biomass.
 Expressed in cm2 g-1 of plant dry weight.
LAR =
Plant dry weight
Leaf area per
plant

66. 66
Leaf Area Duration (LAD)
• To correlate dry matter yield with LAI, Power et al. (1967) integrated the LAI
with time and called as leaf area duration.
• LAD takes into account, both the duration and extent of photosynthetic tissue of
the crop canopy. The LAD is expressed in days.
LAD =
2
L1+L2 x (t2-t1)
L1 = LAI at the first stage
L2 = LAI at the second stage,
(t2-t1) = Time interval in days

67. 67
NET ASSIMILATION RATE(NAR)
The concept was 1st given by Gregory (1918).
 It directly indicates the rate of net photosynthesis.
Formula:
NAR = (W2-W1)(log L2 – log L1)
(t2 – t1) (L2 – L1)
Where
W1 = Dry weight of plant at time one ( in grams)
W2 = Dry weight of plant at time ( in grams)
t 1 = time one ( in days)
t 2 =time two(in days)
Iog =natural logarithm
L1 & L2 = Leaf Area
Unit : g(dry matter production)/ cm2/day