Germination of Seeds

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germination of seeds

Germination of Seeds is the process in which the plant grows from a seed or a similar structure. Researchers and biologists apply this term to the sprouting of a seedling or gymnosperm from a spore.

Germination in simple terms is the growth of plants within the seed. In this process, the radicle and the plumule grow out as the seed grows within the soil.

The seed of a vascular plant is like a small package that sometimes contains food reserves in its seed coat.

The formation of the seed is the result of the male and female cells of the plant that forms in the fruit.

Some plants have a varying number of feeds however, not all of them have embryos and they never germinate.

Dormant seeds are viable seeds that do not germinate as they require specific internal and external stimuli to resume growth.

Formation of Seed

When a fertilized ovule divides by cell multiplication, it forms a seed. It stores food that has the potential to develop into a new plant under optimal conditions.

Fertilization is the process of fusion of male and female gametes to form a zygote.

After reaching stigma, i.e. part of the flower, the male gametes fuse with the egg and forms a zygote.

germination of seeds 1

Thus fertilization takes place and the zygote develops into an embryo.

After the process of fertilization, an ovary of the flower develops into the fruit while ovules develop into seeds.

Therefore, the formation of the seed completes the process of production in plants. The seed within the growing embryo develops and matures under optimal conditions.

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The Process of Seed Germination

The complete process of seed germinations is completed in the following steps:

At the beginning stage of germination, the seed absorbs water and this results in swelling and softening of the seedcoat at optimum temperatures.

This stage is referred to as Imbibition. It is called so as during this stage, it activates the enzymes in the seed.

The seed activates its internal physiology and starts to respire and produce proteins.

germination of seeds 2

As a result, it metabolizes the food already present in the seed. This is, however, the lag phase of seed germination.

After the seed coat ruptures, a radicle emerges to form the primary root of the plant. As a result of this radicle, the seed absorbs water from underground sources.

After the emerging of radicle and plumule, shoots of the plant start growing upwards.

In the final stage of germination. the cells of the seed become active metabolically, elongates, and divides to give rise to the seedling.

Requirement of Conditions for Seed Germination

Seed germination depends on both internal and external factors, however, the most external factors include optimal temperature, water, oxygen or air, and sometimes light or even darkness.

Different plants require varying variables for germination and often depend on the individual seed variety. Moreover, it is also linked to the ecological conditions of the plant’s natural habitat.

For some seeds, external factors affect the process of germination during seed formations, most often these responses are types of Seed Dormancy.

Let us first discuss the conditions seed requires for successful germination.

Water

Seeds require water for germination. Matures seeds are often dry and need to absorb a significant amount of water. However, they need water to moist the surface not soak them.

After the formation of seeds, most plants reserve foods in the form of starch, proteins, or oils in the seeds.

This food reserve provides nourishment to the growing embryo.

germination of seeds 3

When the seed imbibes water, hydrolytic enzymes break down the food into useful chemicals that they require for metabolic activity.

After the formation of seedlings, the process of Photosynthesis starts to provide energy that the new plant requires to grow.

This new plant or selling requires a continuous supply of water, nutrients, and light.

Oxygen

Seeds need oxygen for metabolism. Oxygen is used by it in aerobic respiration, which is the main source of its energy until leaves frow.

Oxygen is an atmospheric gas that is also present in the gaps of the soil. However, if the seed is buried deep within the soil it may starve due to lack of oxygen.

In some types of seed, the seed coat prevents oxygen to enter the seed, causing a type of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange and water uptake from the environment.

Temperature

Temperature affects the metabolic rates and growth of the seedling.

It is important to note that the seeds of the different species or even seeds of the same plants need varying temperatures for growth.

Often seeds have a certain temperature range in which they germinate, however, they will not do so below to above this range.

Many seeds germinate in the temperature range of 0-75 F (16-24 C) while others germinate just above freezing and others in response to slight temperature variations between warm and cool.

Some seeds germinate when the soil is cool from 28- 40 F and others when the soil is warm at 76-90 F. Moreover, some seeds even require cold temperatures to break seed dormancy.

Seeds in a dormant state do not germinate even if the conditions are favorable. Moreover, the seeds that are dependent on temperature to end dormancy have a type of physiological dormancy.

Most common annual vegetables have temperature ranges between 75 – 90 F though some vegetables like spinach and reddish can germinate at significantly lower temperatures for as low as 40 F thus allowing them to grow from seeds in cooler climates.

However, suboptimal temperatures lead to a low success rate and a long period of germination.

Light or Darkness

Light or darkness is a trigger for the germination process and is a type of physiological dormancy.

It does not affect most seeds, however, many seeds including the ones found in forest settings will not germinate until an opening in the canopy allows a significant amount of light for the growth of the seedling.

Some seeds require specific conditions to germinate. For instance, the heat of the fire in many Australian native plants

And some seeds need soaking in a body of water for longer periods of time.

However, other needs to pass from the digestive system of animals so that the seed coat weakens to allow the seedling to emerge.

Soil Surface

Although many times a farmer might want to ow the seed on the soil surface, however, it is recommended to sow them at a certain depth.

soil surface

Planting seeds at a certain depth causes them to use all of their energy before reaching the soil surface. However, planting too shallow can result in insufficient soil moisture.

As temperature and moisture are important for the growth of seed, in the same way, planting depth is important and varies with the plant species.

According to researchers, placing large seeds deeper in the soil because they contain more energy to reach the soil surface than small seeds.

Moreover, many farmers consider other factors like soil type, planting time, and temperature while deciding how deep to plant.

Now let’s discuss Seed Dormancy and Its Effect on Germination

Germination Rate

In agriculture, the germination rate describes how many seeds of a particular plant species, variety, or seed lot are likely to germinate in a given period of time.

It is a measurement of time course and researchers express it in percentage usually. For instance, 85% means that 5 out of 100 seeds will germinate under proper conditions over the period of germination.

The determination of Seed germination rate is by the genetic composition of the seed, morphological features, and environmental factors.

growth rate

However, it is useful for calculating the number of seeds that farmers need for a given piece of land or the number of plants they desire to grow.

The germination rate is the time period for the process of germination from starting time of sowing however the number of seeds able to germinate in a population is, seed capacity.

Seed Dormancy and Its Effect on Seed Germination

Seed dormancy is that under certain conditions seeds do not germinate. Often seed dormancy is divided into 2 categories i.e exogenous and endogenous.

However, there are 3 types of dormancy based on their mode of action:

  1. Physical Dormancy
  2.  Physiological Dormany
  3. Morphological Dormancy.

Moreover, it is important to note that not all seeds undergo a period of dormancy. If the seeds are collected and sown in the ground, in an environment that is warm enough, they will germinate.

However, under natural conditions, non-dormant seeds in the growing season wait till spring when the temperature of the soil rises.

Or the seed disperses during dry periods until it rains and there is enough moisture in the soil.

Exogenous Dormancy: It is the type of dormancy that is because of external factors outside the embryo and into 3 subcategories:

  1. Physical Dormany: The cause of this dormancy is impermeable seed coat and develops during mutation and drying of the seed.
  2. Mechanical Dormancy: In this type, the seed coat or other covering is too hard to allow the embryo to expand during germination.
  3. Chemical Dormancy: It includes growth regulators that are present in the coverings around the embryo.

Endogenous Dormancy: This is the dormancy that is due to the conditions within the embryo itself and into 3 subcategories:

  1. Physiological Dormancy: It prevents the growth of an embryo and seed germination until chemical changes occur.
  2. Morphological Dormancy: The embryo is either underdeveloped or undifferentiated,
  3. Combined Dormancy: Under this type of dormancy, the seeds have both physiological and morphological dormancy.

Controlled Germination for Enhancing the Nutritional Value

Globally, grains such as wheat, rice, maize, oat, barley, rye, sorghum, millet, buckwheat, and quinoa are planted for producing dietary foods and consumed in whole, polished, or milled forms.

Recent studies in nutrition and epidemiology suggest that whole grains offer health benefits to humans and, as a result, their consumption has significantly increased.

Controlled germination is one of the effective methods to enhance the nutritional value of whole grains.

The term controlled germination refers to germination under carefully controlled conditions, and germination is accompanied by the application of environmental stresses that trigger plant defense systems in order to produce and accumulate health-promoting bioactive compounds.

Selection of Seed

Good quality seeds are essential to growing a strong and healthy crop. The selection of seeds to cultivate new crops have to be very careful and of high quality.

Farmers can buy good quality seeds either from different sources or farmers can produce on their own. The selection of seeds is to improve the quality of yields.

Seeds can also be the cause of the transmission of diseases.  If the seeds are from a field that has an infection in them,  then the seed-borne diseases will cause severe problems in the agricultural process.

selection of seeds

Thus, always obtain seeds from healthy plants. Along with the diseases free and healthy seeds, farmers also need to check the germination period of the seeds, nutrients required, and other benefits in terms of yield and finance.

Overall, selecting good quality seeds is essential for growing strong and healthy crops.

Criteria for Selection of Seeds

In order to obtain a healthy crop, farmers need to select healthy seeds. After selection of these seeds carefully for the cultivation of new crops. therefore they should use the following criteria for the selection of seeds.

The seeds should be whole, not broken or crushed, have a high germinating capacity, with a shorter period of germination, and be free from infection.

Moreover, they should give high yields, the seed to be one crop only, bought from a certified agency or a reliable shop.

You can learn about the Fumigation and Sowing methods of seed here.

Conclusion

Germination of Seeds is a crucial process that influences crop yield and quality.

Therefore, understanding the molecular aspects of seed dormancy and germination is of great significance for the improvement of crop yield and quality.

Selecting good quality seeds can help increase the wild of the crop.

It is important to learn about different external and internal factors that affect the growth of the seed as that farmers can increase the yield and in turn meet the food requirements of the people.

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