The document discusses the impact of temperature stress on plant growth and development, focusing on the physiological, morphological, and reproductive effects of both high and low temperatures. It outlines the mechanisms of heat stress, its detrimental effects on yield and quality, and various mitigation strategies such as agronomical adjustments, water management, and protective substances. Additionally, it highlights the symptoms and management techniques for low temperature stress, including chilling and freezing injuries in crops.

1. Temperature stress
in plants
Harithalekshmi V
2018-11-067
Dept. Agrl. Meteorology

2. Significance of temperature on organic life
• Physical and chemical process within the plants are goverened by
temperature
• The diffusion rate of gases and liquids
• Solubility of different substances
• Rate of reactions
• Stability of the enzyme system
• Normally the growth permitting range of
temperature – 10℃- 45 ℃ - Biokinetic zone

3. Cardinal temperature
• The three temperature points viz. minimum ,optimum and maximum
temperature called as cardinal temperature
Crops Maximum ℃ Minimum ℃ Optimum ℃
Cool season cereals
(Wheat,barley,oats)
0-5 25-31 31-37
Warm season cereals
(Rice,maize,sorghum)
15-18 31-37 40-50
(Mavi, 1994)

4. Classification of organisms based on temperature
tolerance
Psychrophiles
15-20oC
Mesophiles
35-45oC
Thermophiles
45-100oC

5. Temperature stress
Low temperature High temperature
Chilling Freezing Heat stress
Stress stress

6. Heat stress
Heat stress is defined as the rise in temperature beyond a
threshold level for a period of time sufficient to cause irreversible
damage to plant growth and development
(Singh, 1973)

7. Effect of heat stress
Physiological changes
Phenological changes
Anatomical changes
Morphological symptoms

8. Physiological
changes
Photosynthesis
Reproduction
Phenology
Mineral
Nutrition
Growth

9. Effect on photosynthesis
• Most heat sensitive physiological processs
• C3 plants will be more affected than C4 plants

10. How photosynthesis is reduced?
Reduces amount
of photosynthetic
pigment
Closure of stomata
lead to reduced
CO2 uptake
Leaf water status is
affected
Chlorophyll
function is affected
Reduced
transcription and
activity of RuBP
Case
Altered structural
organization of
thylakoids
Lipid peroxidation of
thylakoids and
chloroplast membrane

11. (MHRD, 2017)

12. Reduction in plant growth
• Germination is affected the most
• Loss of cell water content
• Reduced net assimilation lead to
reduced relative growth rate
 Reduced germination – Thermoinhibition- increased ABA
 Abnormal seedlings
 Poor seedling vigour
Ambient temperature
Heat stressed

13. Effect on reproductive development
• Reproductive tissues are more
sensitive
• Pollen and spikelet sterility
• Impared pollen germination
• Reduced pollen viability
Splitting of locule at
apical part of theca

15. Effect on plant metabolism

16. Yield
• Increase in temperature by 1℃ will reduce yield of the cereals by
4.1% to 10%
Reduced photosynthesis
Increased respiration
Reduced assimilatory capacity

17. Anatomical changes
• Reduced cell size
• Closure of stomata
• Increased stomatal and trichomatous density
• Greater xylem vessels
• Damaged mesophyll cell and increased permeability of plasma
membrane

18. Phenological changes
• The crop duration was reduced under elevated temperature
(Rani, 2013)
Temperature Duration
Ambient + 4 ℃ 96
Ambient + 2 ℃ 102
Ambient 108

19. Effect of heat stress in various phenophase
Growth stage Threshold temp
(0C)
Symptoms
Emergence 40 Delay &decrease in emergence
Seedling 35 Poor growth of seedling
Tillering 32 Reduced tillering & height
Booting - Decreased no.of pollengrain
Anthesis 33-34 Poor anther dehiscence &sterility
Flowering 35 Floret sterility
Grain formation 34 Yield reduction
Grain ripening 29 Reduced grain filling

20. Effect on mineral nutrition
• High temperature stress causes reduction in absorption and
subsequent assimilation of nutrients
• Absorption of calcium is reduced at temperature of 28 ℃ in Maize
• Nutrient uptake is affected by both soil and air temperature in rice
• Nitrate reductase activity decrease under high temperature

21. Scorching of leaves
Sun burn
Morphological symptoms

22. Leaf senescence
High soil temperature causes stem
scorches
at the ground level
Eg: cotton

23. Sun sclad
Strangulation sickness
Death of yong seedlings when
temp exceeds 46 ℃

24. Effect on produce quality
High temperature stress during post-flowering stage increases
the proportion of gliadins to glutelins and decreases the proportion of
starch hampering the quality of wheat flour and the grain yield
(Ashraf, 2014)

25. Mitigating heat stress
• Avoidance
Mechanisms for surviving which include log term evolutionary,
phenological and morphological adaptations and short term avoidance
or acclimation mechanisms
• Tolerance
Ability to grow and produce yield under HT

26. Avoidance
• Leaf rolling
• Closure of stomata
• Increased stomatal and
trachomatous densities
• Larger xylem vessels
• Waxy cuticle

27. Tolerence – Antioxidative response

28. Heat stress -> Expression of heat shock genes -> Heat shock proteins
Tolerence – Heat shock protein

29. Agronomical method of heat stress mitigation
Sowing time
• Indian farmers adjust sowing time of wheat in such a way, so that crop
escapes to the hot and desiccating winds during grain-filling period
• Early sowing of high-yielding Indian variety of wheat C306
(Coiventry et al. 2011)
Tillage
Zero tillage, bed planting and conventional tillage with mulching
(Kajla et al. 2015)

30. Water Management
• Drip irrigation also helps in maintaining adequate soil moisture and
reduces soil temperature
Foliar Spray
• Potassium fertilizer, urea, zinc, IMCP, and GA3
• Application of nutrients like nitrogen, K, Ca, and Mg decreases the
damaging effects of reactive oxygen species
(Almeselmani et al. 2006)

31. Protective substances
• Millets and wheat seeds – Pre soaked 18-24h - 0.25 M CaCl2
(Genkel et al., 1955)
• 0.05-0.08% ZnSO4 – Sugar beet, Potato, Sunflower
(Petinov, 1961)
• ZnSO4, CaCl2, Ca(NO3)2 – Barley, Wheat
(Onwueme, 1972)

32. Low temperature stress

33. Chilling Stress Freezing stress
Damaging effect of low
temperature above the freezing
point
Damage due to freezing of
intercellular water content into ice
crystals
Due to short term exposure of low
temperature of 0 - 15℃
Temperature below 0℃
Tropical and sub- tropical crops are
affected
All kind of crops mostly seen in
crops grown in temperate regeion
In rice pollen viability is affected
resulting in sterility
In cotton boll fails to open
In castor no seed setting
Field crops sensitive to frost are
wheat, barley, mustard, potato,
peas, winter maize, and tomato

34. Suffocation
• Formation of thick cover of ice/snow on the soil surface presents the
entry of oxygen and crop suffers
Heaving
• Lifting of plants along with soil from its actual position by ice, crystals.
This is a mechanical lifting
Physiological drought and desiccation
• Spring drought- coniferous trees- in cool temperate climate
• Decreased water absorption by plants at low temperature is the
combined effect of the decreased permeability of root membrane
and increased viscosity of water

35. Symptoms of chilling stress
Plant growth and death

36. Surface lesions on leaves and fruits

37. • Abnormal curling, lobbing and crinkling of leaves
• Water soaking of tissues

38. Symptoms of freezing stress in wheat
Tillering
• 12 F (-11 ℃)
• Leaf chlorosis
• Burning of leaf tips
• Silage odor

39. Jointing
• 24 F (-4 C)
• Death of growing point
• Leaf yellowing or burning lesions
• Splitting or bending of lower stem

40. Booting
• 28 F (-2 C)
• Floret sterility
Head trapped in boot

41. Milking
• 28 F (-2 C)
• White awns or white head
• Shrunkened, roughened, or
discolored kernals

42. • Altered date of sowing
• In cotton early planting increases percentage of open ball
• In mustard early planting reduces adverse effect of frost
• Selection of varieties and crops
• Barley and oats are more tolerant than wheat
• Maintaining good crop stand and spacing
• Use high seed rate to cover frost effect on germination
• Adequate inter row spaces should be maintained to allow sunlight incidence and to
increase soil temperature
Agro-techniques for management of Low
temperature stress

43. • Irrigation
• Keep crop well irrigated. Sprinkler irrigation increases canopy temperature
• Delving
• Using of wide blade tyne to mix deep clay soil with sandy top soil
• Delving reduces soil albedo, increases potential to store and release heat by soil
• Covers/thermal blankets for protecting high value crops
• Allow sunlight to penetrate during day and trap radiation at night time by covers and reduces freeze
damage
• Nutrient management
• High N increases vulnerability to frost
• K, Cu and Mo deficiency render crop vulnerable to frost

44. Physical method
• Heaters to reduce temperature inversion
• Cold acclimation
• Evaporation suppressors

45. Cold hardening
Soil banking Wrapping

46. Sprinking
•Keep plant leaf temperature at 1 to 2°C more
•Increases the moisture content of the air and soil
• Thus slowing the rate of temperature drop
•The water absorbs heat during the day which is released slowly at
night

47. Fogging
• Retards the loss of heat from soil and plant
surfaces to the atmosphere
•Applying ground water with an average
temperature of 21°C (70°F) to a greenhouse can
create a ground fog if the ground surface is
several degrees cooler than the water

48. Summary
• Significance of temperature
• High temperature stress
• Low temperature stress
- Cold injury
- Freezing injury
• Mitigation strategies for temperature stress

49. Thank you..