Seed quality: Quality seed is genetically pure, characterized by a high germination percentage and appropriate moisture content; it is free from diseases, and has a high content of pure seeds and no weed seeds.
Why Does Seed Quality Matter?
Seed quality is a key to achieving a uniform crop stand. Seed quality contributes to sustainable agriculture growth, ensuring optimal yields and farm profitability.
Methods of Seed Quality Evaluation
Seed Testing: Seed depends on the different seed testing protocols which determine the genuineness of the cultivar in respect of its properties. It is to maintain good seed quality attributes, viz. Purity, moisture, viability, germination, vigor, and health enable the farming community to get quality seeds.
- Seed quality is the main important component for uniform crop stand. It is determined by Genetic, Physical, Physiological, and pathological factors.
- Genetic factor (Cultivar purity): It is determined by different methods like, the grow-out test (GOT), Molecular method, and chemical method.
- Seed physical factor includes Physical purity test including pure seed, other crop seed, weed seed, and inert matter.
- Seed physiological factor includes seed moisture test, seed vigor test, viability test, etc.
- Pathological factor– Seed health, fungal, Bacteria, viruses, nematodes, and insect damage.
The objective of seed testing:
- Determine adherence to quality standards.
- Identify quality issues and their causes.
Seed sampling
seed sampling is to get a uniform and representative sample from seed lots, to determine the seed quality attributes such as physical purity, germination, moisture, etc.
Seed lot sampling procedures
- Seed testing is based on lots. Seed lot size depends on the size of the seed, bigger the seed, the bigger the seed lot.
- Seed lot: This is defined as a specified quantity of seed, which is physically identifiable and for which an analysis certificate may be issued.
- A small portion taken from one point of the seed lot is term as Primary sample.
- Mixed together from all primary samples taken from a given seed lot is known as a composite sample.
- A sample submitted to the seed testing laboratory for analysis is known as a submitted sample.
Seed lot size
| Type of seeds | Maximum size of a seed |
| Maize | 40,000 kg |
| Cereal, and with seeds larger than cereal seed | 30,000 kg |
| Crops with seeds the size of cereal seeds (other than cereal) | 20,000 kg |
| Crops with seeds smaller that cereal seed | 10,000 kg |
Sampling tools: Trier, bag trier, Nobbe trier, And seed divider.
Physical Purity Test
- It determines the actual proportion of seed in the total seed lot that belongs to the variety for the variety for which testing is being done.
- Components of the seed lot: Pure seed, other crop seeds, inert matter, and weed seeds.
Germination
- Seed germination is the resumption of active growth of the embryo that results in the rupture of the seed coat and the emergence of the young plant.
- The sample size for the germination test should be a minimum of 400 seeds constituted in four replications of 100 seeds, adopted in top of the paper (TP) and between paper (BP) methods based on size, Placed in a Walk-in germinator room in growth cabinets. The temperature of 25 ± 10 0C and RH of 98 percent were maintained during the germination test.
- Germination (%)= Number of seeds germinated/Number of seeds put for germination x100.
Seed germination components:
- Normal seedling– Seedlings have the capacity for continued development into a normal plant when grown in favorable conditions. i.e. seeding is considered normal if 50% or more of the total cotyledon tissue is functional.
- Abnormal seedlings– Seeding is considered abnormal if seedlings grow less than 50%. Seedlings do not grow or develop into normal plants when grown in favorable conditions.
- Hard seed– Seeds that do not absorb water till the end of the test period and remain hard, mainly in leguminosae and Malvaceae.
- Fresh ingeminated seed (FUG)– Seeds other than hard seeds which remain firm and viable but do not germinate within the prescribed period even after treatment for breaking dormancy are recorded as FUG.
- Dead seed- Seeds that at the end of the test period are neither hard nor fresh and also not produced seedlings are classified as dead seeds.
Seed Moisture content (%)
- These methods are used for testing seed moisture content Hot Air Oven method, the Moisture Meter, and the Moisture Analyser.
- The moisture content of the seed was determined by the high constant temperature hot air oven method as per the procedure given in ISTA rules. Five grams of seed was weighed and put in aluminum containers. The seed sample containers were dried in a hot air oven maintained at 130 + 1oC temperature for one hour in most species except cereals and oil seeds. After that, the aluminum containers were cooled in a desiccator for 30 minutes. The MC was determined on a dry weight basis by using the following formula.
- Moisture content (%)= M2-M3/M2-M1 X 100
- Where, W1 – Weight of empty container with its cover (g)
- W2 – Weight of container with its cover and seed sample before drying (g)
- W3 – Weight of container with its cover and seed sample after drying (g)
- If the result of the duplication determination differs by more than 0.2% then the analysis should be repeated in duplication.
- Seeds of some crop species require grinding before the actual moisture content is determined.
- Groundnut, soybean, chickpeas, peas, lentils, and beans require coarse grinding.
- Cotton, maize, oat, barley, rye, wheat, sorghum, and paddy require fine grinding.
Seed viability test
A seed is considered viable when it is live and potentially capable of germination. (Dormant seed is also a viable seed).
- Various methods used for estimating seed viability are germination test, Tetrazolium test (TZ test), membrane permeability test, seed viability test through an automatic seed analyzer, phospholipid determination, lipid peroxidation measurement, estimation of alpha-tocopherol and measurement of respiration by Warburg respirometer.
Seed vigour test
- Seed vigor is the establishment of seeds under unfavorable field conditions.
- Estimating seedling vigor can be classified into the following groups.
- Physical test: seed size, physical soundness of seed, x-ray test.
- Performance test: First count, speed of germination, Seedling growth test, and seedling dry weight.
- Stress test: cold test, brick gravel test, paper piercing test, Accelerated aging test (AA test).
- Biochemical tests: Glutamic acid decarboxylase test (GADA), Respiration and respiratory quotient (RQ), ATP (adenosine triphosphate level test, membrane permeability test.
Also visit Seed Pelleting, Seed storage, Different classes of seeds, Desiccant seed storage (zeolite, silica gel)
Seed Health
Seed health is one of the most important components of seed quality. Disease-causing organisms are fungi, bacteria, viruses, and insect pests. The disease or pest-infected seed plays a major role not only in the loss of crop yield but also in affecting the seed quality.
Factor affecting seed health
- Inadequate crop husbandry: lack of agronomic practices like weeding, intercultural practices, etc.
- Production of crops on sick soil.
- Lack of proper harvest and post-harvest care.
- Poor storage condition.
Seed processing
It is a process that removes undesirable material like inert material, weed seeds, damaged seeds, and other crop seeds. It includes drying, cleaning, grading, treatment, and seed packaging.
Seed drying
Drying of seed to a safe moisture level, seed moisture is very important to maintain the seed viability and vigor. The rate of moisture from the seed depends on temperature, relative humidity, physical structure, chemical composition, and seed coat permeability of seed.
Method of seed drying:
1) Sun drying– It is the most common method of drying. Seeds are sun-dried when the harvested seed has high moisture content. The seeds are spread in thin layers and exposed to the sun for a natural flow of dry air.
2) Forced air drying– The seed is placed in a drying bin. Heated air of recommended temperatures is forced through damp seeds to remove the moisture content.
- The maximum recommended air temperature for seed drying is 40 o c. If seed moisture is more than 18% maximum recommended drying temperature is 32 o c and if lower than 18%, 40 o c is the required air temperature for drying.
- Seed moisture is inversely proportional to drying temperature. If the seed moisture drying temperature should be low, to reduce the risk of damage or cracking.
Seed cleaning
- Remove of undesirable and unwanted physical impurities like damaged or broken seeds of the variety, seeds of other crops, weed seeds, broken plant parts, and inert matter.
- Preconditioning includes all operations, e.g. shelling, debearding, etc. Necessary to isolate the seeds from the plant parts with which these were harvested.
- Pre-cleaning includes the removal of extraneous matter like pieces of trash, stones, clods, etc. Which are either larger in size or the particles that are lighter in weight and smaller in size than the threshed crop seed lot.
- No pre-cleaning is required on hand-harvested.
Seed grading
- Separation of seeds based on seed density and size with the help of a seed grading machine.
Seed treatment
- Seed treatment refers to the application of fungicide, or insecticide to the seeds to disinfect and disinfest them from seed-borne or soil-borne pathogenic organisms and storage insects.
Seed packaging
Packaging or bagging is essentially the last operation in which seeds are handled in bulk flow. Proper labeling of the packaging indicates all the details of seed quality standards on appropriate tags attached to the container. (Check out complete details of seed packing materials).
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