Write important objectives of seed testing along with the methods used for testing of seed viability, seed vigour and genetic purity of a variety.

Objectives of Seed Testing

The primary objectives of seed testing are multifaceted, encompassing quality assurance and farmer confidence. They include:

• Determining Purity: Assessing the presence of weed seeds, other crop seeds, and inert matter.
• Evaluating Viability: Determining the percentage of seeds capable of germination.
• Assessing Vigour: Evaluating the seedling growth potential – speed of germination, seedling health, and overall robustness.
• Verifying Genetic Purity: Confirming that the seed variety maintains its genetic identity and conforms to the established variety description.
• Compliance with Standards: Ensuring that the seed lot meets the minimum standards prescribed by the Seed Act and Rules.

Testing for Seed Viability

Seed viability refers to the ability of a seed to germinate and produce a seedling under favorable conditions. Several methods are employed to assess this:

Tetrazolium (TZ) Test:

This is a rapid and sensitive biochemical test. It involves immersing seeds in a tetrazolium chloride solution, which reduces to a red-colored formazan in viable tissues. The extent of red staining indicates the degree of viability. It's particularly useful for small seeds and seeds with hard coats.

Germination Test:

This is the most common and reliable method. Seeds are placed on a moist substrate (e.g., filter paper, sand) under controlled temperature and humidity conditions. The number of seeds that germinate within a specified period (usually 7-14 days) is recorded. The percentage of germination is calculated. The India Seed (Ornamental Seeds) Rules, 1978, provides specific guidelines for germination testing.

Testing for Seed Vigour

Seed vigour reflects the overall seedling growth potential, extending beyond just germination. It assesses the speed and strength of seedling establishment.

Cool Germination Test:

This test is used to evaluate vigour in seeds that germinate poorly under warm conditions. Seeds are germinated at lower temperatures (e.g., 10-15°C) to identify seeds with slow or weak germination.

Electrical Conductivity Test:

This test measures the leakage of ions from seeds. Seeds with higher vigour leak fewer ions, indicating better membrane integrity. It's a rapid, non-destructive test and correlates well with field performance.

Seedling Growth Rate:

This involves measuring the length of the seedling root and shoot after a specific germination period. A faster growth rate indicates higher vigour.

Testing for Genetic Purity

Maintaining genetic purity is crucial for preserving the desirable traits of a variety. Genetic contamination can occur through pollen drift or accidental crosses.

Visual Purity Assessment:

This involves a physical examination of the seed lot to identify any seeds that differ in size, shape, or color from the standard variety.

Grow-Out Test:

A small sample of seeds is planted in a controlled environment, and the resulting plants are observed for any variation from the expected characteristics. This is the most definitive method for assessing genetic purity. The Seed Act, 1966, mandates grow-out tests for new varieties.

Molecular Marker Analysis:

This is a modern, highly accurate method using DNA markers to identify genetic variations and confirm the variety's identity. This is increasingly used for high-value crops and protected varieties.

Test Type	Parameter Assessed	Method	Advantages	Disadvantages
Viability	Germination Potential	Tetrazolium Test	Rapid, sensitive	Not always reliable for all seed types
Viability	Germination Potential	Germination Test	Reliable, standard method	Time-consuming
Vigour	Seedling Growth Potential	Electrical Conductivity	Rapid, non-destructive	Requires calibration
Genetic Purity	Variety Identity	Grow-Out Test	Definitive	Time-consuming, resource-intensive