Explain internal and external factors affecting seed longevity?
I. External Factors:
(i) Water:
A dormant seed is generally dehydrated and contains hardly 6-15% water in its living cells. The active cells, however, require about 75-95% of water for carrying out their metabolism. Therefore, the dormant seeds must absorb external water to become active and show germination. Besides providing the necessary hydration for the vital activities of protoplasm, water softens the seed coats, causes their rupturing, increases permeability of seeds, and converts the insoluble food into soluble form for its translocation to the embryo. Water also brings in the dissolved oxygen for use by the growing embryo.
(ii) Oxygen:
Oxegen is necessary for respiration which releases the energy needed for growth. Germinating seeds respire very actively and need sufficient oxygen. The germinating seeds obtain this oxygen from the air contained in the soil. It is for this reason that most seeds sown deeper in the soil or in water-logged soils (i.e. oxygen deficient) often fail to germinate due to insufficient oxygen. Ploughing and ing aerate the soil and facilitate good germination.
(iii) Suitable Temperature:
Moderate warmth is necessary for the vital activities of protoplasm, and, therefore, for seed germination. Though germination can take place over a wide range of temperature (5-40°C), the optimum for most of the crop plants is around 25-30°C. The germination in most cases §tops at 0°C and 45°C.
II. Internal Factors:
(iv) 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.
Here is a start:
1. Kind / variety of the Seed
2. Initial Seed Quality
3. Moisture Content
4. Relative Humidity and Temperature During Storage
Seed longevity, or the ability of seeds to remain viable over time, is influenced by a combination of internal and external factors. Internal factors refer to characteristics inherent to the seed itself, while external factors are environmental conditions that can impact seed longevity.
Internal factors affecting seed longevity include:
1. Genetic factors: The genetic makeup of a seed can influence its ability to remain viable. Some plant species naturally produce seeds with a longer lifespan, while others have shorter-lived seeds. This genetic variation is a result of adaptations to specific environmental conditions and reproductive strategies.
2. Seed coat properties: The thickness, toughness, and presence of waxy or protective layers in the seed coat can affect seed longevity. A durable seed coat can provide physical protection against mechanical damage, moisture loss, and microbial attack, thereby enhancing seed longevity.
3. Moisture content: Seeds naturally have a certain moisture content, which can vary depending on the species. High moisture content is generally detrimental to seed longevity, as it can promote fungal and bacterial growth, leading to seed deterioration. Additionally, when seeds dry out too much, it can also negatively impact their viability.
External factors affecting seed longevity include:
1. Temperature: Temperature plays a crucial role in seed longevity. Seeds are typically best preserved at low temperatures, as this reduces metabolic activity and slows down seed deterioration processes. Extreme temperatures, such as freezing or high heat, can damage seed tissues and decrease viability.
2. Humidity: High levels of humidity can promote the growth of fungi and bacteria, leading to seed decay. Conversely, excessively dry conditions may cause seeds to lose moisture and viability. Proper storage conditions, with moderate humidity levels, help maintain seed viability over time.
3. Light exposure: Most seeds are adapted to protect themselves from light because exposure to light can trigger biochemical processes that reduce viability. Therefore, seeds are typically stored in opaque containers or kept in dark, cool environments to minimize the effects of light exposure.
To maintain seed viability, proper storage techniques are essential. Seeds should be stored in a cool, dry, and dark environment. Many gardeners and seed banks use airtight containers such as glass jars or moisture-proof bags with desiccants to control moisture levels. Regular monitoring and periodic testing of seed viability can help determine the need for seed replacement or regeneration.