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Factor affecting of seed germination

Pawan Kumar NagarM.Sc. (Horti.) Fruit science,

IInd SemesterREG. NO: 04-2690-2015

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Factor affecting of seed germination• (A) External factor

(B) Internal factorThe 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

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.

• 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.

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.

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.

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.

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.

Pathogenic organisms

Pathogenic organisms on the seed surface, in the germinating medium, in the irriga tion 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 tem perature condition.

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.

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.

• 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.

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

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.

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