Factors necessary for seed germination
A. External or environmental factors
B. Internal factors
A. External or environmental factors:
The seeds of all species essentially requires at least three external conditions for germination. This four factors are –
2. Suitable temperature
The supply of water is one of the essential requirement in the germination of seed. Water is necessary for the physical and chemical process that take place in the germinating seeds. With the imbibition of water, the seed coat become soften and permeable to water. In their resulting state, seeds are characterized low in moisture and relatively metabolically inactive. Water is also necessary in each stage of germination, starting from imbibition, activation of enzyme, digestion of soluble complex food to soluble forms and translocation to the assimilation into living protoplasm.
The amount and rate of water absorption depend upon the kinds of seed during germination and storage. The rate of water absorption increases with the increase of temperature. Soaking and steeping of seeds before planting is sometime practices to enhance germination. This practices is advantages for seed with hard or dry seed coat or with dormant embryo. Excess water is harmful for the seed germination as most of the seed can not respire under poor aeration condition in germination medium and often over supply of water favours the damping off.
2. Stable temperature:
Temperature affects the absorption of water. The intake of oxygen and chemical reaction in germinating seeds. The temperature requirement for the germination of seed are generally considered in relation to three point/There are 3 stage of temperature such as – minimum, maximum and optimum. Minimum or maximum temperature those below or above the seed germination does not occur. The largest number of seeds and particular species germinate at 26.5 – 36°C may be said as optimum temperature.
The non – dormant seed of small grains, clover, radish, onion etc. germinate at very close to 20°C. Spinach seed germinate at 10°C or very close to 20°C.
Freshly harvested seeds of cucumber and water melon germinate at high temperature of 30°C. Wheat seed (slightly above 35°C) and maize seeds (5 – 45°C) germinate at wide range of temperature.
Commonly used practices are 15°C or 20°C for 16 – 18 hours and 30°C for 6 – 8 hours. The effect of alternating temperature on germination is called thermoperidism.
Oxygen is an essential requirement in respiration which supply energy to remain life by oxidation of foods. During germination the oxidation rate increases.
C6H12O6+ 6O2 6CO2+ 6H2O + 673 kCal energy
Oxygen uptake is increase and Carbon di – oxide is given off at an increased rate. Oxygen is responsible in some way in regarding the initial reaction of germination.
Reduced aeration decrease the germination rate seeds of water plant and rice seed can normally germinate under water. The ability of rice seed to germinate at low oxygen presence due to the presence of an anaerobic condition energy liberating system within the seeds.
Visible light can stimulate or inhibit the germination of some plant species. Epiphytic plant have an essential requirement for light. While light inhibits the germination of some plant species i.e. Allium amaranthus etc. Light also favours the germination of lettuce, tobacco and cauliflower.
Germination is controlled by a photochemical reversible reaction which involves the response of a pigment (Phytochrome) to light of certain wave length.
in red light
Phytochrome Phytochrome (far red)
(Inhibits germination) (Promotes germination)
Imbibe seeds when exposed to red light (wave length 6400 – 6700 Å) the phytochrome (red) is instantly change to phytochrome (far red) which is associated in some way with inducing germination.
The following internal factor play important role for successful germination in the seed.
1. Presence of auxin.
2. Reserved food
3. Completion of dormancy
4. Viability of seed
1. Presence of auxin:
During germination a chemical called auxin, develops in the seeds which stimulates germination. In addition to increase another substance known as heteroauxin develops in some seeds. Both auxin and heteroauxin are called growth regulator.
2. Presence of reserved food:
Foods are stored in the endosperm (monocot seed) or cotyledons (dicot seed). Embryo is dependent on the reserve food. Germination is possible if the seed is able to provide with necessary food to the embryo.
3. Completion of dormancy:
The inhibit growth of seed due to some internal causes even through the environmental condition of available for germination is called dormancy. So during the dormant period of seed complete breaking of dormancy must be essential.
4. Seed viability:
Viability refers the seeds whether a seed is alive, dormant or dead. If the seed is not viable it will not germinate.