seed

Question 1

Reproduction in Plants

Answer 1

Plants reproduce sexually by seeds and asexually by vegetative parts. Seeds are used for multiplication, while grains are for human or animal consumption.

Question 2

Importance of Seeds

Answer 2

Good planting materials are crucial to profitable crop production, determining the quality and quantity of the produce.

Question 3

Characteristics of Good Seed

Answer 3

A good seed must be genetically satisfactory, fully developed, free from contamination, deformities, diseases, and pests.

Question 4

Seed Structure

Answer 4

A seed is a fertilized ripened ovule with three main parts: seed coat, endosperm (food storage organ), and embryo.

Question 5

Seed Types

Answer 5

Seeds can be exalbuminous (no endosperm at maturity, e.g., beans) or albuminous (endospermic, e.g., maize).

Question 6

Role of Seeds

Answer 6

Seeds are carriers of new technology, tools for food security, aids in crop yields, and essential for agricultural rehabilitation after disasters.

Question 7

Characteristics of Quality Seed

Answer 7

Quality seeds should be pure, viable, free from disease, uniform in size, and have high germination rates and moisture levels between 8-12%.

Question 8

Advantages of Good Seeds

Answer 8

Good seeds offer uniform germination, reduce replanting, ensure strong seedling growth, and maintain quality under storage.

Question 9

Seed Treatment

Answer 9

Seed treatment involves applying chemicals, nutrients, hormones, or protectants to control diseases and pests. Methods include dry, wet, slurry, and pelleting treatments.

Question 10

Seed Selection

Answer 10

Seed selection is critical to ensure high-quality, disease-resistant seeds that are free from weed contamination and provided by certified agencies.

Question 11

Genetic Purity

Answer 11

Genetic purity is the percentage of contamination by other varieties, beginning with the seed planted and affected by prior crops, pollen transfer, and handling.

Question 12

Isolation in Seed Production

Answer 12

Fields must be isolated by distance or flowering time to ensure pollination occurs only among plants of the desired variety and avoid contamination.

Question 13

Classes of Seed

Answer 13

The four recognized classes of seeds are Breeder’s seed, Foundation seed, Registered seed, and Certified seed.

Question 14

Breeder seed

Answer 14

Breeder seed is the seed directly controlled by the originating or the sponsoring breeder or institution which is the basic seed for recurring increase of foundation seed

Question 15

Foundation seed

Answer 15

is the progeny of breeder seed
The seed stock is handled to maintain specific identity and genetic purity, which may be distributed and produced under careful supervision of an agricultural experiment station
This seed is the source of all other certified seed classes.

Question 16

Registered Seed

Answer 16

Registered seed is the progeny of foundation seed, maintained for genetic purity and certified by a certifying agency with a minimum purity of 99%.

Question 17

Certified Seed

Answer 17

Certified seed is the progeny of registered or foundation seed, grown under prescribed conditions, inspected for purity, and used for commercial planting.

Question 18

Formal Seed System and informal seed system

Answer 18

A centrally planned, mechanized system with quality control, certified seeds, and large-scale marketing by national agencies and private companies.

informal seed system - A locally planned, unmechanized system using local resources, traditional processing, farmer exchanges, and community-level marketing.

Question 19

SEED DORMANCY

Answer 19

**Seed dormancy is defined as a seed failing to germinate under environmental conditions optimal for germination, normally when the environment is at a suitable temperature with proper soil moisture
This true dormancy or innate dormancy is therefore caused by conditions within the seed that prevent germination

Thus dormancy is a state of the seed, not of the environment
Induced dormancy, enforced dormancy or seed quiescence occurs when a seed fails to germinate because the external environmental conditions are inappropriate for germination, mostly in response to conditions too cold or hot, or too dry

Question 20

Seed dormancy has two main functions

Answer 20

the first is synchronizing germination with the optimal conditions for survival of the resulting seedling; the second is spreading germination of a batch of seeds over time so that a catastrophe after germination (e.g. late frosts, drought,hervivory) does not result in the death of all offspring of a plant

Question 21

Often seed dormancy is divided into four major categories

Answer 21

exogenous; endogenous; combinational; and secondary
A more recent system distinguishes five classes of dormancy: morphological, physiological, morphophysiological, physical and combinational dormancy

Question 22

Exogenous

Answer 22

Physical dormancyorhard seed coatsoccurs when seeds areimpermeable to water
At dormancy break, usually in response to environmental cues, especially temperature, water can enter the seed and germination can occur
Plant families where physical dormancy occurs includeCannaceae,FabaceaeandMalvaceae

Chemical dormancy: species that lack physical dormancy, but where a chemical prevents germination
This chemical can be leached out of the seed by rainwater or snow melt or be deactivated
Leaching of chemical inhibitors from the seed by rain water is often cited as an important cause of dormancy release in seeds of desert plants

Question 23

Endogenous dormancy

Answer 23

Endogenous dormancy is caused by conditions within the embryo itself, including:
Morphological dormancywhere germination is prevented due to morphological characteristics of the embryo
In some species the embryo is just a mass of cells when seeds are dispersed, it is not differentiated. Before germination can take place both differentiation and growth of the embryo have to occur
In other species the embryo is differentiated but not fully grown (underdeveloped) at dispersal and embryo growth is required before germination can occur

Question 24

Physiological dormancy

Answer 24

Physiological dormancymeans that the embryo, due to physiological causes, cannot generate enough power to break through the seed coat, endosperm or other covering structures
Abscisic acid is usually the growth inhibitor in seeds and its production can be affected by light
Drying : some plants including a number of grasses need a period of drying before they will germinate
Many herbaceous plants from temperate climate zones have physiological dormancy that disappears with drying of the seeds

Question 25

Combinational dormancy

Answer 25

In seeds with combinational dormancy the seed or fruit coat is impermeable to water (physical) and the embryo has physiological dormancy
Depending on the species physical dormancy can be broken before or after physiological dormancy is broken

Question 26

Breaking seed dormancy

Answer 26

Scarification
Hot water treatment
Acid treatment
Other chemicals

Question 27

Scarification

Answer 27

Scarification
Mechanical scarification is a technique for overcoming the effect of an impermeable seedcoat
Mechanical scarification can be done by rubbing seeds between two pieces of sandpaper or using a file to rupture the seed coat
Seed may also be mixed with coarse sand and rubbed or shaken vigorously
Large seeds like those of lupin can be easily scarified

Question 28

Hot water treatment

Answer 28

For small to medium-sized seeds, hot water treatment is more practical than scarification
For this treatment seeds should be dipped in 82-95oC pre-heated water (time depends on species)
Seeds should be left to cool, then soak in normal water for 12 to 24 hours, after which they are ready for sowing
With hot water treatments, the seeds should be sown promptly and not stored again

Question 29

Acid treatment

Answer 29

Acid treatments are often used to break down especially thick impermeable seed coats, e.g. Sulfuric acid
The acid should be used at room temperature for a period of a few minutes to several hours depending on the species
The seeds should be immersed in acid in a glass, or earthenware container, and should be stirred occasionally
Seeds should be removed promptly and washed thoroughly in several changes of water to neutralize
Seeds can be sown immediately or stored

Question 30

Other chemicals

Answer 30

Three chemicals that have proven very helpful in breaking certain types of dormancy are gibberellic acid (GA3), potassium nitrate, and thiourea
The aqueous solutions of these chemicals should be used at room temperature
The concentration and length of treatment depends on the species to be treated