Print 
Details: Category: Quality Seed | Published: 16 May 2013 | Hits: 6401

Factors affecting seed quality:

Genetic factors
•         Seed size
•         Bulk density
•         Differences in dormancy levels

Physical or environmental factors
•         Quality of seed at the point of sowing
•         Injury during planting and establishment
•         Growing conditions during seed development
•         Nutrition of the mother plant
•         Damage during harvesting and post harvest processing/handling
•         Maturity of seed at harvest
•         Pest and disease damage
•         Moisture and temperature during storage
 
Characteristics of Good Seed
•         High germination potential
•         Minimal contamination with inert material and non-target species/varieties
•         Minimal damage through mechanical, pests and diseases
•         Uniform seed size
 
Seed certification
The purpose of seed certification is to ensure continued supply of quality planting material. For farmers to realize high crop yields and hence value for their investment, use of quality planting material is critical. In Kenya, seed quality is monitored regulated by Kenya Plant Inspectorate Service (KEPHIS). To ensure that only quality seed reaches the market, KEPHIS oversees and inspects seed production processes all the way from site selection, to land preparation,  planting, harvesting, processing and packaging.
 
Seed production
The criteria for selecting fields for seed production include
1.    Should not have been grown with rice for the previous year (unless it was the same variety planted for certification and met inspection requirements for varietal purity)
2.    Should be separated from other fields of same variety by a ditch, road or barren strip of at least 5 meters distance to prevent contamination.
3.    Should be located in the region where the crop will be grown to minimize spread of diseases and pests.

Field/water management
1.    Good land preparation should be done to kill volunteer plants and control weeds.  Fields should be cultivated or chemically treated with herbicides to ensure that weeds and volunteer rice plants do not seed.
2.    Good water management is required for irrigated species during vegetative, flowering and ripening phases. More water is needed at flowering, less water at ripening and moderate water during vegetative growth phase. During vegetative phase, water should be managed in such a way as to prevent late tillering to ensure uniform ripening.

Harvesting and post harvest management
Harvesting should be done when 80% of the panicles are golden brown. Avoid rainy days and contact with moisture once the stalks are cut. Thresh immediately after cutting the stalks to avoid quality deterioration. The threshed material should be winnowed, sorted and graded to remove all foreign material and half-filled and unfilled seeds.
 
Seed dressing, packaging and storage  
To protect seed from insect and fungal attack during storage, the material should be dressed with appropriate pesticides (insecticides and fungicides). Dry the treated seed to below 11% moisture content to avoid infestation and improve on longevity. Appropriately package seeds in hermetic container (one that does not allow seeds to reabsorb water) and store in a dry cool environment.

Evaluating for high quality

To assess seed quality, KEPHIS undertake several tests including:
1.    Varietal purity test
2.    Germination test
3.    Seed health
4.    Seed purity

Germination test

Germination test is recommended before sowing using the following procedures below:-

* Count 100 seeds
* Soak the seeds for 24 hours
* Wrap the seeds in a wet paper or cotton wool
* Incubate for 2 days
* Count the number of seeds that have germinated
* Seeds with more than 80 % of germination percentage are recommended to ensure high ratio of germination.


There are set standards for the above quality attributes; high quality should conform to varietal descriptor, and be free from off types, inert material such as leaves and stones, weed seeds, diseased seeds, deformed seeds, and seeds of other varieties. The allowed minimum germination is 80%. The Table below summarizes the set standards for quality attributes in respect of the various seed classes
 
Table1: Accepted set standards for seed quality attributes*

Factor

Breeder`s

Foundation

Registered

Certified

Off types %

0.0

0.02

0.03

0.03

Inseparable other plants %

-

0.01

0.05

0.05

Objectionable weeds %

-

0.01

0.02

0.02

Diseased plants/Head

-

0.01

0.05

0.05

 

 

 

 

 

Seed labeling

Test results of the seed quality should be recorded and labeled  by seed producers on the seed containers. The other information that is recorded on the containers include:
1.    Seed lot number
2.    Spacing requirement
3.    Yield potential per acre
4.    Appropriate region/Eco-zone
 
For more information