Seed Treatment

For many higher plants, the seed is the starting and the conclusion of their life cycle. Seeds are extremophiles, which can withstand extremes of temperature, desiccation, and air pressure. They are the most excellent means of survival for species and populations because of these characteristics. The ovule of the plant grows into a seed after fertilisation, which would be distributed from the parent plant and eventually germinate, resulting in the growth of a new plant.

Seed Treatment

Seed treatment can be defined as a condition in which seeds are prevented from germinating under favourable conditions such as temperature, light, water, gases, seed, coats, etc. Seeds require an ample amount of time before they are fully capable of germinating. The time may differ from several days to months, and it may even take years. These factors include hormones, heat, water, light, etc. 

Methods of seed treatment

There are several methods used for breaking seed treatment. These are as follows:

Scarification: This refers to the process by which hard, outer coverings of seeds are softened to help them absorb water better, eventually leading to germination.

Here, a hard seed coat is rubbed on sandpaper or cracked with a hammer. These methods are effective for a small amount of relatively large seeds. On a large scale, mechanical scarifiers are used.

Acid scarification: Dry seeds are placed in the ratio of one part of the seed to two parts of acid (HCl or H2SO4) in glass, earthenware, wood, or plastic containers. The time taken to complete the process varies, depending upon the species, from 10 minutes to 6 hours. The acid is poured off, and the seeds are washed to remove the acid in the last step. Seeds of legumes, brinjals, and tomatoes are treated with this type of treatment.

Hot water scarification: Seeds are dropped into hot water with temperatures ranging from 77 to 100 ℃. The seeds are then left to soak in heated water after the source has been turned off. This allows them to swell. With the help of a suitable screen then, unswollen seeds are removed.

Warm moist scarification: Seeds are placed in a warm medium to soften the seed coat. This treatment is beneficial for seeds with a double seed treatment.

Stratification: It is a method of handling dormant seeds in which they are subjected to chilled temperatures for a specific time after the embryo ripens. It is also known as moist chilling.

Stratification is further divided into the following types:

1. Outdoor stratification: In this process, the seeds are stored in a deep pit surrounded by wooden frames, dug in a field. This pit or tray provides moisture to the seeds when irrigated at regular intervals.
2. Refrigerated stratification: This is an alternative to outdoor stratification. It is useful for tiny seeds that require special handling. Dry seeds are imbibed with water via refrigerated stratification for twelve to twenty-four hours. Twenty-four hours of soaking is sufficient for seeds without hard seed coats. Here seeds are treated at low temperatures usually between 4 and 7℃. At higher temperatures, seeds sprout prematurely, whereas low-temperature delays sprouting.
3. Leaching of inhibitors: Some inhibitors of phenolic compounds present in seed coverings inhibit germination. As such, leaching them helps wash the seeds. 
4. Pre-chilling: Here, seeds are soaked at 5-10 ℃ for 5-7 days in the field.
5. Pre-drying: This acts as a valuable method to overcome treatment. Seeds are subjected to a temperature of 37-40 ℃ for 5-7 days before sowing.
6. Seed priming: Freshly harvested fruits overcome treatment by this method. This is the most widely used method consisting of procedures like Osmo- conditioning, infusion and fluid drilling.
7. Hormonal treatment: Among various hormones, GA is used for breaking seed treatment in different seeds. Cytokinin is another hormone that breaks physiological treatment and stimulates germination in seeds. Kinetin and BAP (BenzylaminoPurine) have been commercially used for breaking seed treatment.

Advantages of seed treatment:

1. Germination occurs only when there are favourable conditions present for seedlings.
2. Helps in creating a seed bank.

Conclusion :

We can conclude from the above discussion that seed treatment allows seeds to overcome unfavourable conditions that hinder their growth. Seed treatment finds essential applications in plant ecology and agriculture. Several processes and methods discussed helped overcome the period of treatment and thus switch from the dormant to the germination stage.