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PRODUCTION OF QUALITY SEED




  • INTRODUCTION

    With the increased access to the information technology, the farmers are becoming more aware of the importance of quality in seed. The growers demand high quality seed that is capable of healthy and uniform emergence in the fields. Quality seed is one of the cheapest and most essential input for crop production.

    The subject covers two aspects, quality which is an integral part of seed production. The quality traits that a seed lot intended for multiplication must meet follow:

    Seed quality

    Seed quality refers to the planting value of the seed. Seed is a living embodiment possessing production potentials and other traits like disease and insect resistance and quality etc. It is a vehicle of continuity of inherited characters and software of translating breeder’s efforts into crop production in the field. The seed must possess some measurable attributes, which help determine its value for sowing.

    Components of seed quality

    Following are the most important quality characteristics for sowing. Inferior quality in any one characteristic may result in low yields and poor quality of the produce. The ultimate aim of seed certification and testing is to make available high quality seed possessing the following indicators:

    1.Analytical purity

    2.Species purity

    3.Cultivar purity

    4.Freedom from weeds

    5.Germinating capacity

    6.Vigor

    7.Size

    8.Moisture content

    9.Homogeneity

    10.Health

    1.   Analytical purity (Physical or mechanical purity). 

    Analytical purity is the most important component of seed quality. It indicates how much of the seed material of the species named on the label is intact. It protects the farmers against the use of impure and adulterated seed having contamination of other crop species and inert matter etc. Analytical Purity has definite standards for various crop species, generally not less than 98%.

    2.   Species purity

    It resembles analytical purity except for degree of admixture of other crop seeds like barley in wheat.

    3. Varietal purity (cultivar purity) 

    All field crop species have a number of varieties with different agronomic and botanic characteristics. Varietal purity refers to the genetic purity ascertained in the field, by examining growing plants, because as a general rule, varieties cannot be identified by an examination of their seeds in the lab except those possessing distinct characteristics.

    4.   Freedom from weeds

    Weeds are a very serious problem of seed crops. So weed seeds are taken separately then other species. Weed seeds are present in almost all seed lots. There are some weeds that are very common and can be tolerated subject to the standards, but there are other weeds, which are noxious in nature and should be completely absent from the sowing seed. What is of importance is not the weight of weed seeds that is sown in a field but the number.

    5.             Germination capacity.

    The germination capacity indicates the potential of a seed lot to establish seedlings under good field conditions. A lot with high purity will be of no use for sowing if the seeds are incapable of germinating and producing strong seedlings in the field. The germination capacity of a seed lot is the percentage by number of pure seeds, which produce normal seedlings in a laboratory test.

    Germination capacity is the most important characters of a seed lot, so a seed lot with a higher germination capacity will always prove to establish more seedlings then the lot with a lower germination capacity.

    6.             Vigor

    The germination capacity of a seed lot is the ability of producing normal seedlings under good field conditions, whereas the vigor represents its ability to do so under poor conditions. Seed lots with same germination capacity, especially with low percentage may perform differently under adverse or abnormal field conditions.

    Generally, high germination capacity is associated with high vigor. There is no standard vigor test however; high germination capacity may be taken as a good indication of vigor. Therefore, high germination should be preferred while purchasing the seed for sowing.

    7.             Seed size

    Large seed size is taken as indication of vigor. The seeds contain an embryo alone or with endosperm as reserved food for developing seedlings. The bigger the size of seed, the greater will be the size of seedling with larger leaf area for photosynthesis. Further, a large seed if sown deep into the soil have more chances to reach the surface then a smaller one.

    In fact, it is not necessary that large seed size always produce higher yields. In wheat, it has been observed that plants from small seeds having similar populations and good field conditions can produce an equivalent yield of grain as large seeds. Seed size is expressed as the weight of a thousand seeds, 000 seed weight, or g/1000 seeds.

    8.             Moisture content

    Moisture content is very important. It is the key factor in determining whether or not the seed will retain its germination from harvest to sowing time. Moisture can be determined in the laboratory. Moisture meters can help make quick on the spot assessment of moisture expressed as percentage by weight.

    9.             Homogeneity (Uniformity)

    The seed lot must be homogenous for its components. Every seed lot may have some mixture of inert matter, other crop and weed seeds. To make the contents of a seed lot consistently uniform, it should be thoroughly blended and made homogeneous before packaged and marketed.

    10.          Health

    Seed health is important in controlling certain diseases particularly the seed-borne diseases, where the infection is carried over from one year to the next by the seeds like cereal smut and bunt. It is possible to identify most of the pathogens in the laboratory. Seed-borne diseases can be controlled by chemical treatment of the seed. Nevertheless, it would always be a good policy to use seed harvested from healthy crops.

    SEED PRODUCTION

    A seed program aiming at producing seed with the above cited quality traits must comprise of the following components:

    A.Variety development and maintenance system.

    B.Seed regulations.

    C.Seed standards.

    D.Production and quality control organizations.

    A.            Variety development and maintenance system

    There is a wide range of institutions engaged in variety development and research, working on Federal, Provincial, autonomous and semi-autonomous levels (four Agricultural Universities, 13 multi-disciplinary research institutes and 31 mono-commodity research institutes). The research system has successfully developed and releases over 400 varieties of major crops in Pakistan. There are many new varieties in the pipeline.

    Variety maintenance is an integral part of the modern seed production system. All registered and released varieties recommended for cultivation are required to be maintained true-to-type. The varieties are maintained true to their registered characteristics.

    Seed Regulations

    It is not possible to judge the quality of seed just from the appearance. A seed lot with very poor germination capacity may appear to having very good looks. Planting of such seed means net loss to the farmer both of investment and the expected produce. To control and regulate such matters and to protect the farmer’s interests, appropriate regulations are required. The regulations in vogue are:

    1.MINIMUM SEED STANDARDS: Comprising minimum standards for inspection of seed fields and testing of seed lots of various field and vegetable crops. According to the Seed Act, 1976, certified is voluntary whereas labeling of seed offered for sale is obligatory.

    2.TRUTH-IN-LABELING RULES: The quality of the seed to be marketed is indicated on the label. The truth of the label is subject to verification by the Federal Seed Certification & Registration Department.

    3.RULES FOR HORTICULTURAL PLANTS: The rules and standards for registration of fruit nurseries and quality of seedlings are being introduced in the country.

    4.PLANT BREEDERS’ RIGHTS: To encourage plant breeding and investment in this sector, the legislation on the Plant Breeders’ Rights is in the final stages with the Government.

    Seed standards

    Seed production system in Pakistan follows the generation system, almost on the same lines as on international level by ISTA and OECD member countries. In this system the seed class changes to the next lower class at every re-generation. A seed crop seeded with pre-basic seed will produce basic seed, which in turn will yield certified seed. Each category of seed is tested and examined according to the prescribed standards. The seed standards followed in Pakistan are of international level. Following classes of seed are recognized in Pakistan:

    1.     Pre-basic

    2.     Basic

    3.     Certified

    4.     Approved

    SEED production STRATEGY

    To produce and market seed of the above cited categories, the following points must always be applied:

    1SELECTION OF LAND: It is very important in quality seed production. The following points must be kept in view while selecting land for a specific seed production plan:

    a.The land must be free from weeds and volunteer plants of the same crop.

    b.Knowledge of cropping history of seed field is important. Ordinarily any crop must not follow the same crop. Exception is only to the seed crop seeded with the same variety of equal or higher seed class-cereals and pulses etc.

    c.Research areas and experimental stations must preferably not be used for seed production except the land meets the seed production requirements.

    2The pre-basic seed must invariably be produced by the breeder following proper maintenance of the variety seed stocks true-to-type.

    3The multiplication of basic seed must also be controlled and supervised by the breeding and seed production staff specially trained for this purpose. The production of seed and the production of commercial crop can involve two completely different technologies.

    a.The seed growers in comparison to the commercial producers in general are more quality than quantity conscious.

    b.In seed production, maximum yield per acre is not as important as the maximum multiplication rate i.e. seed yield/plant.

    c.To achieve a rapid multiplication the seed rate is usually reduced to harvest maximum seed per plant.

    d.The more rapid the increase, the sooner the country will benefit from a newly released improved variety.

    e.The seed production of majority of cereals and pulses, although appears to be similar to commercial production of grain crop yet requires special care and attention regarding land selection and crop purification etc.

    4AREA: The seed production must preferably be arranged in the area of adaptability where the soil and environmental conditions are most conducive. It will help prevent gene shifts and excessive losses from environmental hazards like frost and drought etc.

    5SOIL: Quality of the soil also plays a major part in the selection of seed production areas. Normally the soils commanding relatively high water holding capacity are preferred for growing seed crops.

    6SITE: The site selected for seed production must be easily accessible and not prone to pest and disease, floods, wild boar and rodents etc.

    7IRRIGATION: Availability of Irrigation water is very important. Irrigated sites are preferred our rainfed to avoid stresses at critical stages of crop growth and seed development.

    8LABOR: Labor for various field operations must be available at hand from the neighbourhood.

    9SEED GROWER: Seed grower is the most important person in quality seed production. A good seed grower can be distinguished from commercial crop producer by his attitude towards off-types and contaminants in the field and seed.

    10INPUTS: Fertilizers and other inputs must be applied in such a way that maximum seed yield could be obtained.

    11SOWING: The seed crops must be sown rather early in the season so as to permit maximum growth and development of plants. Planting seed crops in rows wider than normal crop facilitates better weed control, easy crop inspection and rouging, and satisfactory plant protection.

    a.ROGUING: Roguing is carried out to improve the varietal purity to the desired level. It is an act of purifying seed crops of a variety through removing by hand the undesirable individual plants whose seed cannot be easily and completely removed during conditioning or using preventive measures. Roguing is also referred to as “negative selection”. Roguing of off-types is the main difference between seed production and grain production.

    12PLANT PROTECTION: Notwithstanding the use of resistant varieties is most appropriate for controlling insects and diseases, yet application of chemical pesticides and herbicides may be necessary. For this purpose proven and recommended chemicals must be used. In most cases seed treatment is advised.

    13HARVESTING: Seed health and vigor are at their peak at physiological maturity and starts deteriorating as the harvesting is delayed. Therefore, it is essential to harvest the seed crop at the right stage of maturity. Extreme care must be exercised to physical admixtures during harvesting and threshing. All the equipment used for harvesting and threshing must be properly cleaned before use. The adjustment of the threshing machine must be carefully adjusted to prevent any damage to the seed.

    14SEED CONDITIONING: Generally mechanical removal of contaminants present in a seed lot is termed as seed conditioning or seed processing. Common contaminants removed through processing are weed seeds, plant parts, soil particles and other non-plant materials.

    15STORAGE: There are large variations as regards storage requirements of various crop seeds. The most important consideration is to avoid heating up of the seed lots, which may occur as a result of high moisture contents, microorganism and insect activities.

    Production and quality control organizations

    The Seed Act, 1976 is public oriented and silent about the induction of private sector, however, the Federal Government allowed private sector participation in the seed industry by making new rules under section 29 of the Act. Consequently, in addition to four public organizations, there are now about 600 private sector seed companies registered for seed production and marketing.

    The responsibility of providing quality control through variety registration, crop inspection, seed testing and seed law enforcement is with the Federal Seed Certification and Registration Department.

    References

    Thomson, J.R. 1979. An Introduction to Seed Technology. Thomson Litho Ltd. East Kilbride, Scotland. UK.

    Copeland, L.O. 1976. Principles of Seed Science and Technology. Burgess Publishing Company, Minneapolis, Minnesota. USA.

    Feistritzer, W.P. 1975. Cereal Seed Technology. A Manual of Cereal Seed Production, Quality Control, and Distribution. FAO, Rome.

    Van Gastel, A.J.G. and J. Kerley. 1986. Quality Seed Production. Seed Technology Course, Cairo, Egypt, 15-30 March 1986.

    Ahmad, S.I. 1994. Legume Seed Technology. Proceedings of FSC&RD/ICARDA Train-the-Trainer Course, 5-14 April 1994, Sahiwal. FSC&RD, Islamabad.

    Van Der Burg, W.J. Aspects of Seed Quality Control. Seed Production Technology, ICARDA, Aleppo. Syria.

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