Factor affecting of seed germination

2. Factor affecting of seed germination
Pawan Kumar Nagar
M.Sc. (Horti.) Fruit science,
IInd Semester
REG. NO: 04-2690-2015
PRESENTED BY

3. Factor affecting of seed germination
• (A) External factor
(B) Internal factor
The following environmental factors influence germination and seedling growth:
(A)External factor
 Also known as environment factor.
 Most important factor affecting germination of seed are following:
• Water
• Temperature
• Aeration
• Light
• Salinity
• Pathogenic organisms

4. Water
 Water is required for germination. Mature seeds are often extremely
dry and need to take in significant amounts of water, relative to the
dry weight of the seed, before cellular metabolism and growth can
resume.
 Most seeds need enough water to moisten the seeds but not enough
to soak them.
 The uptake of water by seeds is called imbibition, which leads to
the swelling and the breaking of the seed coat.
 When seeds are formed, most plants store a food reserve with the
seed, such as starch, proteins, or oils.

5. • This food reserve provides nourishment to the growing embryo.
• When the seed imbibes water, hydrolytic enzymes are activated
which break down these stored food resources into
metabolically useful chemicals.
• After the seedling emerges from the seed coat and starts
growing roots and leaves, the seedling's food reserves are
typically exhausted; at this point photosynthesis provides the
energy needed for continued growth and the seedling now
requires a continuous supply of water, nutrients, and light.

6. Aeration
 Germinating seeds respire at a very high rate.
 Thus adequate supply of oxygen is necessary for germination to take place and
the seedling to grow.
 Germination rate and germination percentage of most kinds of seeds are
adversely affected if the germinating medium is poorly aerated.
 In seed-beds that are over-watered or poorly drained with clayey soil, the soil
pore spaces may be so filled with water that oxygen supply to the seeds is retarded
or prevented.


7. A notable exception is rice seeds which have an anaerobic respiration
that permits germination in water-logged soils.
 Similarly, seeds of many other species such as lettuce, celery, carrot,
beet, portulaca, petunia, etc. require comparatively less oxygen during
germination and hence, these seeds germinate well even in poorly
drained soils.
Apple seeds germinate better in hypoxia (2, 5 and 10% 02) than in air
or in atmosphere enriched with oxygen.
Come et al. (1985) found that breaking of dormancy in apple seeds by
cold treatment was due to reduction of the noxious effect of high
oxygen concentration.

8. Temperature
The temperature influences strongly the percentage and rate of seed
germination, the optimum temperature varying with the kind of seeds.
 In general, seeds of cool-season crops, such as lettuce, celery, etc.
germinate best at relatively low temperature of 0 to 10°C, whereas
seeds of warm-season crops like pumpkin, bottle gourd, etc. require
relatively high temperature ranging from 20 to 30°C.
Seeds of several other species germinate over a wide range of
temperatures. Many other kinds of seeds germinate better when the
temperature fluctuates daily about 10°C between maximum and
minimum.

9. Salinity
Soil salinity and poor quality water used to irrigate the seed beds often
retard or prevent germination.
Salinity problems become severe when the germination medium is
lightly and frequently watered; evaporation of water leaves salt
deposits on the soil surface. Small, shallowly sown seeds are likely to
be damaged by salts.
 This problem can be solved by using soils with adequate organic
matter, and irrigation water low in salts, with holding fertilizers and by
irrigating more copiously but less frequently so that excess salts are
leached out.

10. Pathogenic organisms
Pathogenic organisms on the seed surface, in the
germinating medium, in the irrigation water or on the
tools may cause low germination and rotting of
seedlings.
The situation is known as damping-off and is
aggravated by high moisture and high temperature
condition.

11. Light or darkness
•Light or darkness can be an environmental trigger for
germination and is a type of physiological dormancy.
• Most seeds are not affected by light or darkness, but
many seeds, including species found in forest settings,
will not germinate until an opening in the canopy allows
sufficient light for growth of the seedling.

12. Internal factors
 Seed Dormancy Due to Internal Conditions and Its Release
•In some plants the embryo is not fully mature at the time of
seed shedding.
•Such seeds do not germinate till the embryo attains maturity.
• The freshly shed seed in certain plants may not have
sufficient amounts of growth hormones required for the
growth of embryo.
•These seeds require some interval of time during which the
hormones get synthesized.

13. •The seeds of almost all the plants remain viable or living for a
specific period of time.
•This viability period ranges from a few weeks to many years.
Seeds of Lotus have the maximum viability period of 1000
years. Seeds germinate before the ending of their viability
periods.
•In many plants, the freshly shed seeds become dormant due to
various reasons like the presence of hard, tough and
impermeable seed coats, presence of growth inhibitors and the
deficiency of sufficient amounts of food, minerals and
enzymes, etc.

14. Gibberellic Acid
•Gibberellic Acid-3 (Ga-3): GA-3 is a naturally
occurring plant growth regulator. Presoaking
seeds in GA-3 will often cause rapid germination
of many highly dormant

15. Viability of the seeds
•After the seeds are produced they remain
viable i.e. they have potential to germinate
up to certain period that varies from plant to
plant or seed to seed.

16. Treatments helping for seed germination
• Hot Water SoakTreatment
• Dry Heat
• Warm Moist Treatment
• Smoke Treatment
• Hard Seeds-Chipping
• Hard Seeds-Soaking
• Stratification (cold treatment)