Major seed quality characters
Seed quality is the possession of seed with required genetic and physical purity that is accompanied with physiological soundness and health status. The major seed quality characters are summarized as below.
- Physical Quality: It is the cleanliness of seed from other seeds, debris, inert matter, diseased seed and insect damaged seed. The seed with physical quality should have uniform size, weight, and colour and should be free from stones, debris, and dust, leafs, twigs, stems, flowers, fruit well without other crop seeds and inert material. It also should be devoid of shriveled, diseased mottled, moulded, discoloured, damaged and empty seeds. The seed should be easily identifiable as a species of specific category of specific species. Lack of this quality character will indirectly influence the field establishment and planting value of seed. This quality character could be obtained with seed lots by proper cleaning and grading of seed (processing) after collection and before sowing / storage.
- Genetic purity: It is the true to type nature of the seed. i.e., the seedling / plant / tree from the seed should resemble its mother in all aspects. This quality character is important for achieving the desired goal of raising the crop either yield or for resistance or for desired quality factors.
- Physiological Quality: It is the actual expression of seed in further generation / multiplication. Physiological quality characters of seed comprises of seed germination and seed vigour. The liveliness of a seed is known as viability. The extent of liveliness for production of good seedling or the ability of seed for production of seedling with normal root and shoot under favorable condition is known as germinability. Seed vigour is the energy or stamina of the seed in producing elite seedling. It is the sum total of all seed attributes that enables its regeneration of under any given conditions. Seed vigour determines the level of performance of seed or seed lot during germination and seedling emergence. Seed which perform well at sowing are termed as quality seed and based on the degree of performance in production of elite seedling it is classified as high, medium and low vigour seed. The difference in seed vigour is the differential manifestation of the deteriorative process occurring in the seed before the ultimate loss of ability to germinate. Difference in seed vigour will be expressed in rate of emergence, uniformity of emergence and loss of seed germination. Hence it is understood that all viable seeds need not be germinable but all germinable seed will be viable. Similarly all vigourous seeds will be germinable but all germinable seed need not be vigourous. Physiological quality of seed could be achieved through proper selection of seed (matured seed) used for sowing and by caring for quality characters during extraction, drying and storage. Seed with good vigour is preferable for raising a good plantation as the fruits, the economic come out are to be realized after several years. Hence selection of seed based on seed vigour is important for raising perfect finalize plantation.
- Seed Health – Health status of seed is nothing but the absence of insect infestation and fungal infection, in or on the seed. Seed should not be infected with fungi or infested with insect pests as these will reduce the physiological quality of the seed and also the physical quality of the seed in long term storage. The health status of seed also includes the deterioration status of seed which also expressed through low vigour status of seed. The health status of seed influences the seed quality characters directly and warrants their soundness in seed for the production of elite seedlings at nursery / field.
Importance of quality seed
- Ensures genetic and physical purity of the crops
- Gives desired plant population
- Capacity to withstand the adverse conditions
- Seedlings produced will be more vigourous, fast growing and can resist pest and disease incidence to certain extent
- Ensures uniform growth and maturity
- Development of root system will be more efficient that aids absorption of nutrients efficiently and result in higher yield.
- It will respond well to added fertilizer and other inputs.
- Good quality seeds of improved varieties ensures higher yield atleast 10 – 12 %
Hence the quality seed should have
- High genetic purity
- High pure seed percentage ( physical purity)
- High germinability
- High vigour
- Higher field establishment
- Free from pest and disease
- Good shape, size, colour etc., according to the specification of variety
- High longevity / shelf life.
- Optimum moisture content for storage
- High market value
Higher genetically purity:
- Breeder /Nucleus – 100%
- Foundation seed – 99.5%
- Certified seed – 99.0%
Higher physical purity for certification
- Maize , Bhendi – 99%
- All crops ( most) – 98%
- Carrot – 95%
- Sesame, soybean & jute – 97 %
- Ground nut – 96 %
Possession of good shape, size, colour, etc., according to specifications of variety
- Higher physical soundness and weight
- Higher germination ( 90 to 35 % depending on the crop)
- Higher physiological vigour and stamina
- Higher storage capacity
- Free from other crop seeds ( Expressed in number /kg) – Other crop seeds are the plants of cultivated crops found in the seed field and whose seed are so similar to crop seed that is difficult to separate them economically by mechanical means. Eg. Mixtures of Wheat, oats seeds in barley.
- It should be free from objectionable weed seeds -These are plants of weed species which are harmful in one or more of the following ways.
- The size and shape of their seeds are so similar to that of the crop seed that is difficult to remove their seed economically by mechanical means.
- Their growth habit is detrimental to the growing seed crop due to competing effect.
- Their plant parts are poisonous or injurious to human and animal beings
- They serve as alternate hosts for crop pests and diseases.
- It should be free from designated diseases – It refers to the diseases specified for the certification of seeds and for which certification standards are to be met with . These diseases would cause contamination, when they are present in the seed field or with in the specified isolation distance ( eg. loose smut of wheat). For this the the certification distance has been prescribed as 180 meters.
- It should have optimum moisture content for storage – Long term storage – 6 – 8 % , Short term storage – 10 – 13%
- It should have high market value
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