Flooding and temperature stresses are two major abiotic stresses that affect plant growth and productivity. Flooding stress occurs when plants are subjected to excess water, such as flash flooding or prolonged waterlogging. It can lead to oxygen deficiency, wilting, nutrient deficiencies or toxicities. Temperature stresses include high temperatures, which can damage seedling establishment, photosynthesis and reproduction, and low temperatures, which cause injuries like leaf lesions and stem cracking. Farmers can mitigate these stresses through drainage, shade, regulated irrigation, and application of hormones, osmoprotectants and other chemicals.

1. Contd……….
Classification of Stress Caused
in Plants

2. 2. Flooding stress
Flooding may be defined as any situation of excess water.
Sudden shower following high rainfall events also poses a severe
physiological stress on crops.
The gradual shower of crop lands that occurs in a more regular
cycle of seasonal changes in river levels and associated gradual
flooding of crop lands poses a different, but equally challenging.
Flooding environment to which plants must adapt, a a result some
plants, such as rice, evolve a semi aquatic habit.

3. Flooding stress in terrestrial species is referred to as water logging
and the damage symptoms caused are primarily due to the
prolonged exposure of the plants to oxygen deficient.
The effect of water logging of roots and lower stems are apparent
as a range of symptoms on the shoots, including rapid wilting and
severe physiological disruption.
Vast areas of rainfed crops, particularly in South and Southeast
Asia, are annually affected by flooding.

4. Types of floods
Flooding can be tragic, with flash floods causing major soil erosion
and direct physical destruction of crops.
There are two typical kinds of flood.
One is short duration over a few weeks and not very deep, termed as
‘flash flood‘ and
the other is deep flooding that lasts for a long time, called as ’deep
water flood‘.

5. Flash floods are unexpected and uncontrollable, and its flooding
water level can reach 50 cm in the rainfed lowlands of the humid
and semi humid tropics of South and Southeast Asia.
In these areas, flash floods at the seedling stage of rice cause
severely reduced yields of rice grain.

6. Effects of flooding stress on plants
 Decay and death of leaves
 Wilting
 Abscission
 Epinasty
 Lenticels formation
 Nutrient deficiency & Toxicity: Under the anaerobic condition Fe
toxicity is high. This leads to increase the polyphenol oxidase
activity, leading to the production of oxidized polyphenols. It also
causes leaf bronzing and reduced root oxidation power.

7. Iron toxicity symptoms during flood
Tiny brown spots on lower leaves starting from tip and spread toward the
leaf base or whole leaf colored orange yellow to brown.
Spots combine on leaf interveins and leaves turn orange brown and die.
Leaves narrow but often remain green.
In some varieties, leaf tips become orange yellow and dry up.
Leaves appear purple brown if Fe toxicity is severe.
Stunted growth, extremely limited branching.
Coarse, sparse, damaged root system with a dark brown to black coating
on the root surface and many dead roots.
Freshly uprooted plants often have poor root systems with many black
roots.

8. Mitigation of flooding stress
Providing adequate drainage for draining excessive stagnating water
around the root system.
Spray of growth retardant of 500 ppm cycocel for arresting apical
dominance and thereby promoting growth of laterals.
Foliar spray of 2% DAP + 1% KCl (MOP).
Spray of 0.5 ppm brassinolide for increasing photosynthetic activity.
Foliar spray of 100 ppm salicylic acid for increasing stem reserve
utilization under high moisture stress.

9. Foliar spray of 0.3 % Boric acid + 0.5 % ZnSO4 + 0.5 % FeSO4 +
1.0 % urea during critical stages of the stress.
Balance the use of fertilizers (NPK or NPK + lime).
Apply sufficient K fertilizer.
Apply lime on acid soils; do not apply excessive amounts of organic
matter (manure, straw) on soils containing large amounts of Fe and
organic matter.

10. 3. Temperature stress
Greaves (1996) defines suboptimal temperature stress as any
reduction in growth or induced metabolic, cellular or tissue injury that
results in limitations to the genetically determined yield potential,
caused as a direct result of exposure to temperatures above or below
the thermal thresholds for optimal biochemical and physiological
activity or morphological development.

11. Types of temperature stress
Levitt (1980) classified plants into psychrophiles, mesophiles, and
thermophiles to whether or not they tolerate low, medium or high
temperatures.
Psychrophiles are those plants whose high temperature threshold is
15 to 20°C,
Mesophiles are those plants whose high temperature threshold is 35
to 45°C and
Thermophiles are those plants whose high temperature threshold
ranges from 45 to 100°C.

12. A)High temperature stress
High temperatures may be experienced by plants on a daily or
seasonal basis.
There is also growing evidence of long-term climatic changes leading
to both higher average temperatures, widening the geographic range
where high temperatures become routinely limiting to crop
production, and increasing the frequency and severity of extreme
temperature events.

13. Effects of heat stress on plants
 Seedling establishment is hampered
 Drying of leaf margins and scorching effect on leaves
 Reduction in plant growth
 Pollen development is affected
 Alteration in photosynthesis
 Total biomass is reduced
 flower sterility
 Grain and fruit development and quality is affected

15. Mitigation of high temperature stress
 Plants need to be cultivated under shade condition.
 Overhead irrigation to avoid sunburn.
 Application of Gibberellic acid stimulates the α–Amylase
production for seed germination.
 BAP reduce the leaf senescence & lipid peroxidation.
 Salicylic acid enhances the thermo tolerance capacity.
 Glycine betaine reduced the leakage of ion.
 Application of ethylene enhance the seed germination

16. B) Low temperature stress
Low temperatures can damage plants both by a chilling effect
leading to physiological and developmental abnormalities and by
freezing causing cellular damage directly or via cellular dehydration.
Lyons (1973) described many symptoms of low-temperature
injury. Some physiological processes such as flowering in rice are
extremely sensitive to low temperatures and damage may occur at
temperatures as high as 20°C.

17.  Commonly visible symptoms of low temperature injury to the
leaves include wilting, bleaching due to photo oxidation of
pigments, water logging of the intercellular spaces, browning, and
eventually leaf necrosis and plant death.
 Dudal (1976) estimated that 15 percent of arable land is affected
by freezing stress.

18. Effects of low temperature stress on plants
 Reduced plant growth and death
 Surface lesions on leaves and fruits
 Abnormal curling, lobbing and crinkling of leaves
 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)

19. 8. Cucumber Sunken pits
9. Banana Browning of sp skins and degradation
of pulp tissue
10. Pine apple Blackheart

20. Mitigation of low temperature stress
 Foliar spray of 0.15 % Ammonium molybdate reduces the low
temperature stress effect.
 Pre-soaking treatment with GA3 and proline increase the seed
germination.
 Application of paclobutrazol increases the activity of scavenging
enzymes.
 Electrolyte leakage is reduced by the application of uniconzole (50
ppm).
 Cryoprotectants also used for reducing the stress effect.
 ABA has a role in induction of freezing tolerance.