Seed deterioration is a cumulative process that increases a seed's vulnerability over time. It decreases a seed's ability to survive and is an undesirable aspect of agriculture. Seed deterioration is separate from seed development and germination. Several factors influence seed deterioration rates, making it difficult to critically evaluate. Moisture content and storage temperature greatly impact seed life, with lower levels extending life. Damage mechanisms differ depending on whether seeds are dry or wet.

2. • Seed deterioration can be defined as deteriorative
changes occurring with time that increase the
seed’s vulnerability to external challenges and
decrease the ability of the seed to survive.
• Seed deterioration is an undesirable attribute of
agriculture
• The physiology of seed deterioration is a separate
event from seed development and/or germination
• Seed deterioration is cumulative process.

4. • The following thumb rules by Harrington are useful measures for
assessing the effect of moisture and temperature on seed storage.
• For every decrease of 1% seed moisture content, the life of the seed
doubles. This rule is applicable when moisture content between 5
and 14%.
• For every decrease of 5°C (10°F) in storage temperature the life of
the seed doubles. This rule applies between 0°C to 50°C.
• Orthodox – the seeds able to tolerate moisture loss and less seed
moisture favours the storage. i.e. decreased moisture increased
storage period. Eg. Rice, sorghum , and most of the cultivated
species.
• Recalcitrant – just opposite to the orthodox. Seeds not able to
tolerate moisture loss. Required high moisture for viability
maintenance. Ex- Mango, Citrus

5. Facts about Seed Detoriation
• Seeds generally exhibit an initial period of
deterioration under dry storage during which
germination percentage is relatively constant,
but germination rate decreases.
• Cellular damage accumulates in dry seeds,
repair processes following imbibition can
successfully restore a functional physiological
state, up to a certain point, and allow
germination to be completed.
• Seed damage in lag period is reversible.

6. • Seeds should be stored at <50% RH.
• Accelerated ageing 75-100 % RH
• It is equally important to distinguish between
damage that occurs in the dry state and that which
occurs subsequently upon imbibition.
• Seeds vary in their resistance to aging.

7. Why it is difficult to critically evaluate seed
deterioration ?
• The physiological processes governing seed
deterioration vary.
• The rate of seed deterioration is influenced by
confounding environmental and biological factors such
as growth of storage fungi that create their own
biological niche.
• Seed treatments influence seed deterioration, and, when
applied, their impact on seed quality must be
recognized.
• Most seed deterioration studies examine whole seeds.
• Most seed deterioration studies report effects on a seed
lot, but seed deterioration is an individual event.

8. • Enzyme activities: increases in amylase activity
or changes in free radical scavenging enzymes such as
superoxide dismutase, catalase, peroxidase, and others.
• Protein or amino acid content: The
consensus is that overall protein content declines while
amino acid content increases with seed aging.
• Nucleic acids: A trend of decreased DNA synthesis
and increased DNA degradation has been reported.
• Membrane permeability: Increased membrane
permeability associated with increasing seed
deterioration

9. Hydration levels and deterioration and protection
mechanisms in seeds

10. • Some enzymes have activity near level II range.
• The rates of reaction are extremely low or are limited to
the lipid phase.
• Below an equilibrium RH of about 50% (depending upon
the temperature), glass formation can occur, further
increasing viscosity and limiting mobility of molecules.
• Between 70 and 90% RH (hydration levels II and III),
some enzyme activities can be detected (at very low rates)
• The minimum limit for respiration is about 90% RH
• Higher rates of respiration and protein and nucleic acid
biosynthesis only become possible as water availability
increases to hydration level IV
• Active physiological processes only occur in hydration
level V, or above 99% RH

12. Deterioration Mechanisms in dry seed
• Oxidative and peroxidative processes play the primary
roles in initiating the damage that occurs in dry seeds.
• Free radicals can be generated spontaneously, and can
trigger oxidation of various seed constituents.
• At the lowest seed moisture contents, the extreme
viscosity of the glassy state restricts the molecular
motion and diffusion of substrates
• But the availability of oxygen and its tendency to form
reactive oxygen species allow free radical reactions to
occur in a slower rate.
• Presence of solvent water tends to quench free radical
mechanisms and enable antioxidant mechanisms to be
effective.

13. • Peroxidation of lipids, initiated by the abstraction of a
hydrogen by a hydroxyl radical, can result in a chain
reaction that causes breakdown of the lipids
(particularly unsaturated lipids) and release of by-
products such as reactive aldehydes that can cause
further damage to proteins and nucleic acids.
• Changes in membrane lipids due to peroxidation may
be involved in the increase in membrane permeability
and cellular leakage that is associated with seed aging.
• Changes in membrane lipids due to peroxidation may
be involved in the increase in membrane permeability
and cellular leakage that is associated with seed aging.
• At the low water contents of dry seeds, enzymic
mechanisms to regenerate antioxidants are inoperative

14. Deterioration Mechanisms in wet seed
• Hydrolytic reactions become possible as free
water becomes available.
• Metabolic imbalance has been proposed as a
possible cause of damage during dehydration
• Lipid phase transitions also occur in this range of
hydration, as sufficient water is present to reverse
the water replacement by sugars and amphiphiles
that stabilize bilayer membrane structures in dry
seeds.
• Holding seeds in hydration level III results in
rapid deterioration, particularly at elevated
temperatures

15. Methods for testing seed detoriation
• Germination test
• Tetrazolium test
• Vital colouring test
• Enzyme activity test
• Electrical conductivity
test
• Free fatty acid test
•Hydrogen peroxide test
•Indoxyl acetate test
•Fast green test
•Ferric chloride test
•Sodium hypochlorite test
•Excised embryo test
•X-ray Test

16. Loss of viability

17. REPAIR OF SEED DAMAGE
• Increasing seed moisture content hastens the
repair process.
• Oxygen also increases the repair of
highmoisture (27-44 %) lettuce and high-
moisture (24-31 %) wheat seeds, suggesting
that respiratory activity is an essential
component of repair.
• Repair of seeds deteriorated by lipid
peroxidation occurs during hydration.