AGRONOMIC
PRINCIPLES OF SEED PRODUCTION
Standardized seed production, besides
genetic principles involves the application of the following agronomic
principles to preserve good seed quality and high yield.
1. Selection of
a Suitable Agro-climatic Region:- A crop variety to be grown for seed production
in an area must be adapted to the photoperiod and temperature conditions
prevailing in that area. Regions of moderate rainfall and humidity are much
more suited to seed production than regions of high rainfall and humidity. Most
crops require a dry sunny period and moderate temperatures for flowering and
pollination. Excessive dew and rain can cause hindrance in normal pollination
resulting in poor seed set. If hot dry weather conditions prevail during flowering,
many crops such as vegetables, legumes and fruit trees fail to set seed
effectively and produce many seedless fruits. In wind pollinated crops bright
sunny weather with gentle winds which cause an even flow of pollen over crop
during flowering is conducive to best pollination and good seed set. Apart from
pollination, excessive rainfall leads to a higher incidence of diseases and
makes seed harvesting extremely difficult. It is clearly evident that ample
sunshine, relative moderate rainfall and the absence of strong winds have
decided advantages for productive and high quality seed production and must be
kept in view in the selection of the areas for seed production.
2. Selection of Seed
Plot:-
The plot selected for seed crop must have following characteristics:- a) soil
texture and fertility of plot should be according to the requirement of the
seed crops. b) The seed plot should be free from volunteer plants, weed plants
and other crop plants. c) The soil of the seed plot should be free from soil
borne diseases and insect pests
3. Isolation of Seed Crop:- The
seed crop must be isolated from other nearby fields of the same crop and other
contaminating crops as per requirements of certification standards. The
isolation of seed crop is usually done by providing distance between seed
fields and contaminated fields. In hybrid maize seed production if the distance
isolation is not feasible, isolation requirement could be reduced in certified
maize seed production by planting additional border rows. After seed crop has
been harvested isolation of seed produced of different varieties is necessary
to avoid mechanical contamination. Similarly bags or other containers used to
hold the seed must be carefully cleaned to remove seed which may have remained
in the bags from previous lots.
4. Preparation of Land:- The
land for seed crop must be prepared well. Good land preparation helps in
improved germination, good plant stand & establishment and destruction of
potential weeds. It also aids in water management and good uniform irrigation.
5. Selection of Variety:- The variety for
seed production must be carefully selected. A) The variety should be adapted to
agro-climatic conditions of the region. B) The variety should be high yielder.
C) The variety should posses other desirable attributes, namely disease
resistance, earliness, grain quality
6.Seed:- The
seed used for raising a seed crop should be of known purity, appropriate class
and invariably obtained from an authorized official agency. While buying the
seed the following factors should be carefully examined. A) the seed of the
appropriate seed class is bought for raising a foundation seed crop, seed of
the breeder’s seed class is required and for
raising a certified seed crop the seed of the foundation seed class is
required for sowing. B) The tag and seals of the breeders/ foundation seed bags
purchased are intact. C) the validity period has not expired. D) all the bags
are of the same variety.
7. Seed Treatment: - The
seed may require seed treatment before planting, if they are not already appropriately treated.
This could be easily done with help of a revolving drum at the farm. Depending
upon the requirement one or more of the following seed treatment may be
given: a) chemical seed treatment b)
bacterial inoculation for legumes. c) seed treatment for breaking dormancy due
to hard seededness.
8. Time of planting:- The
seed crops should invariably be shown at their normal planting time. Depending
upon the incidences of diseases & pests, some adjustment of early sowing
could be made if necessary. At the time of planting there should be sufficient
soil moisture for germination.
9. Seed Rate:- Lower seed rates than
usual for raising commercial crop are desirable because they facilitate rouging
operations and inspection of crop.
10. Method of Sowing:- The seed crops should be sown in rows with the exception of
thickly sown crops where the sowing could be done by broadcasting. The most
efficient and ideal method of sowing is by mechanical drilling, as it allows
the deposit of the seeds in desired amount at uniform depth. It is of utmost
important to ensure that the seed drills/planters are absolutely clean, i.e
free from left over seeds of other crops. The sowing of seed crops in rows
helps in conducting effective plant protection measures, rouging operations and
field inspections. for hybrid planting of two parents namely female parent line
& male parent line has to be done in a definite proportion 4:2 or 6:2. It
is imperative to ensure that the seeds of male & female parent line do not
get mixed while planting. After planting of male and female lines six to eight
border rows of the male parent may also be sown if required. After sowing male
rows should be marked to facilitate later operations.
11. Depth of Sowing:- Depth of sowing is
extremely important in ensuring a good plant stand. Small seed should usually
be planted shallow, but larger seeds could be planted a little deeper. Seeds
would emerge from greater depths in sandy soils than in clay soils and also in
warm soil as compared to cold. In dry soils seeds should be planted slightly
deeper as so that they come in contact with moisture.
12. Roguing:- Adequate and timely rouging is
extremely important in seed production. As mentioned earlier the rogue which
differ from normal plant population in being weak or sickly or bolters or
dissimilar may cause quick deterioration in seed stocks by cross pollination,
transmission of diseases etc. These plants therefore be removed at earliest
possible date before flowering. It is wise to remove the whole plant and not
just the flower head. The number of rouging necessary will vary with the crop.
Rouging in most of the field crops may be done at any of the following stages.
A) Vegetative/ pre-flowering stage B) Flowering stage C) Maturity stage
13. Supplementary Pollination:- Provision
of honey bees in hives in close proximity to the seed fields of crops largely
cross-pollination by insects, ensure good seed set and thereby greatly increase
seed yields.
14. Weed Control:- Good weed control is a
basic requirement in producing good quality seed. Weeds may cause contamination
of the seed crop in the following ways in addition to reduction in yield. a)
The presence of weed seeds at the time of crop harvest leads to mixing of weed
seeds with crop seeds. In many instances it is difficult to remove them during
the processing of seeds. b) The presence of weeds in the seed field or nearby
areas may serve as source of diseases. good and effective weed control
therefore would be necessary to obtain good seed yields and to avoid
contamination.
15. Disease & Insect Control:- Successful
disease and insect control is another important factor in raising healthy seed
crops. Apart from reduction in yield, the quality of seeds from disease and
insect damaged plants is invariably poor. Poor disease and insect control
affects seed quality in following three ways:- a) there are a number of
diseases which are systemic, if these are not checked the seed produced will
get infected with spores of such diseases and produce diseased plant in next
season, b) there are certain diseases which are not systemic, leave their
spores on seed coat, if not checked this results in a greater susceptibility to
various seedling diseases which can affect the crop. c) Seed yield and quality
are reduced. Following principles may be adopted for an effective management of
diseases and pests in seed crops- a) plant only treated seed, b) prepare and
adopt appropriate schedule of spraying for effective disease and insect control,
c) rouging of diseased plants and ear heads from time to time also helps in
checking the further spread of diseases.
16. Nutrition:- In the nutrition of seed crops
nitrogen, phosphorous, potassium and several other elements play an important
role for proper development of plants and seeds. It is therefore advisable to
know and identify the nutritional requirement of seed crops and apply adequate
fertilizers. Adequate fertilization results in maximum yields, good seed
quality and better expression of plant type.
17. Irrigation:- It has been stressed earlier that
comparatively dried regions are more suitable for good quality, disease free
seed production. In such regions irrigation is essential to obtain good seed
yields. The irrigations may be required before planting and at intervals up to
flowering. One or two irrigations beyond flowering are desirable. In general
lighter soils need more irrigation than heavier soils.
18. Harvesting Of Seed
Crops:-
Time of Harvest:- The optimum time of harvest
is when the seed is fully mature, when weather damage has just begun and the
seed is easily harvested and cleaned
resulting in minimum harvest losses. Harvesting at earlier stages makes
combining difficult and relative losses due to threshing and cleaning are
greater. Similarly harvesting at a late stage may result in increased weather
damage to seeds and losses due to shattering of seeds and lodging of plants in
the field. The optimum harvest time is somewhere between these two extremes.
Method of Harvesting:- In India harvesting of crop is done by hands. This if done at
appropriate time gives good quality of seed. However the subsequent quality of
seed is dependent upon the handling of harvested crop and the care taken during
threshing. Every effort should be made to avoid chance mechanical mixing,
mechanical injury to seed during threshing. Precautions must be taken to adjust
the combines properly so as to keep various losses and mechanical injury to
seed during combining.
19. Drying Of Seeds: - The seed lots are usually at high moisture content at the time of
harvesting and threshing. In order to preserve seed viability & vigour, it
is necessary to dry seeds to safe moisture content levels. Important
precautions to be taken in this respect area-a) care should be taken to ensure
that mechanical mixture does not takes place, b) drying of seeds to safe
moisture limits should be done. If the seeds are to be artificially dried they
should be supplied to processing plants soon after harvesting.
20. Storage of Raw Seeds:- The best method of storing seed for short
period is in stacks or bags in ordinary building or godowns. After sun drying
the seed should be filled in neat and clean bags. If old bags are to be used,
they should be properly cleaned and treated before use. Each and every bag
should be marked appropriately. The stacks of bags should be made on wooden
pallets. The godowns to be used for storage should be dry, cool, clean, sprayed
with Malathion & later fumigated as and when necessary.
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