Chapter 9 - Propogation from seed

Question 1

What 3 conditions must be fulfilled for germination to occur?

Answer 1

1. The seed must be viable;
2. The seed must be subjected to the appropriate environmental conditions.
3. dormancy must be overcome.

Question 2

What is a seed?

Answer 2

A seed is a ripened ovule. and consists of an embryo and stored food supply, both of which are encased in a protective covering

Question 3

What is the difference between primary and secondary dormancy?

Answer 3

secondary dormancy only develops under unfavorable environmental conditions.

Question 4

dormancy

Answer 4

The condition where seeds will not germinate even when the environment is suitable for germination.

Question 5

imbibition

Answer 5

a seeds initial rapid increase in water uptake.

Question 6

seed leakiness is due to…

Answer 6

amino acids, organic acids, inorganic ions, sugars, phenolics, and proteins can be detected as they leak from imbibing seeds. the inability of
cellular membranes to function normally until they are fully hydrated

Question 7

seeds that are more leaky or slow to germinate are…

Answer 7

more susceptible to fungi and insect attack.

Question 8

In germination what part of the embryo first emerges from the seed?

Answer 8

The first visible evidence of germination is protrusion of the radicle.

Question 9

What is the difference between hypogeal and epigeal germination?

Answer 9

hypogeal is where the root and shoot (hypocotyl hook) emerge at the same time while epigeal is where the root emerges followed by the epicotyl (often above ground) cotyledons remain in seed coverings.

Question 10

the radical is the tip of the first emerging plant structure.

Answer 10

of the adventitious root

Question 11

The hypocotyl is

Answer 11

the stem section between the cotyledons and the radicle.

Question 12

cryptogeal germination

Answer 12

germination of the bunya pine where the emerging root develops into a tuber from which the sprout will later grow.

Question 13

What are the 3 main storage reserves in seeds?

Answer 13

1. proteins
2. carbohydrates (starch)
3. lipids (oils)

Question 14

What are 3 important measurement parameters of seed germination?

Answer 14

1. Percentage
2. Speed (Rate)
3. Uniformity

Question 15

Germination percentage

Answer 15

For example, if 75 seeds germinate from

a seed lot of 100 seeds, the germination percentage would be 75 percent

Question 16

Germination speed

or rate

Answer 16

is a measure of how rapid a seed lot germinates.

Question 17

Germination uniformity

Answer 17

measures how close in time seeds germinate or seedlings emerge.

Question 18

T50

Answer 18

time to 50% germination

Question 19

What are 4 environmental factors that impact germination?

Answer 19

1. temp
2. water
3. gases
4. light

Question 20

optimum temp for germination?

Answer 20

between 25 and 30°C although variable

Question 21

alternating temperatures effect of seed germination?

Answer 21

often gives better results for both seed germination and seedling growth.

Question 22

What is seed priming?

Answer 22

is a form of controlled seed hydration that can improve the germination properties of a seed lot

Question 23

here are 3 main techniques for seed priming. What are they?

Answer 23

1. Osmotic priming by imbibing seeds in osmotic solutions.
2. Matrix priming using solid carriers with appropriate matric potential.
3. Drum priming that hydrates seeds with water in a tumbling drum.

Question 24

What is the main way that O2 can become limiting during germination?

Answer 24

Oxygen supply is limited where there is excessive water in the germinating medium.

Question 25

Light sensitive seeds are usually what size?

Answer 25

characterized by being

small in size, and a shallow depth of planting is an important factor favoring survival

Question 26

What is damping-off?

Answer 26

the death of small seedlings resulting from attacks by fungi.

Question 27

Physical Dormancy

Answer 27

Seeds with physical dormancy fail to germinate because seeds are impermeable to water. Physical dormancy is most often caused by a modification of the seed coverings (seed coat or pericarp)

Question 28

What is a water gap in a seed?

Answer 28

a single layer of cells which act as a water gap. often called a hilum.

Question 29

macrosclereids

Answer 29

pallisade cells which contribute to hard seededness and water impearmiabiliy.

Question 30

Leaching can help break what type of dormancy?

Answer 30

secondary dormancy

Question 31

What is the most common type of dormancy?

Answer 31

physi-ological dormancy. The basic model for maintenance of physiological dormancy is that the embryo lacks the growth potential to allow the radicle to escape the restraint of the seed coverings

Question 32

physiological dormancy

Answer 32

A condition mainly controlled by factors within the embryo that must change before the seed can germinate.

Question 33

morphological dormancy

Answer 33

Seeds that have an embryo that is less than one-quarter of the size of the seed when it is shed from the plant.

Question 34

What is seed stratification?

Answer 34

is the process whereby seed dormancy is broken through cold treatments in order to promote germination.

Question 35

What is meant by after-ripening?

Answer 35

used to describe changes that occur in seeds during dry storage that lead to dormancy release.

Question 36

Photodormancy is dependent on what pigment?

Answer 36

phytochrome. Seeds that require light or dark conditions to germinate are called photodormant,

Question 37

n seeds with intermediate physiological dormancy the dormancy is usually broken by ____________

Answer 37

chilling stratification

Question 38

How do deep and intermediate PD seeds differ?

Answer 38

usually require a relatively long (8 to 20 weeks) period of moist-chilling stratification to relieve dormancy.

Question 39

What 2 hormones are most important in seed germination?

Answer 39

ABA and Gibberellin

Question 40

Growth potential

Answer 40

is the force used by the radicle to penetrate the seed coverings (see Fig. 6).

Question 41

Abscisic Acid (ABA) role in seed dormancy

Answer 41

ABA plays a major role in preventing “precocious ger-mination” of the developing embryo in the ovule. ABA increases during late stages of seed development and is a major factor in the induction of primary dormancy

Question 42

Gibberellins (GA) are important for seeds in

Answer 42

both the control and promotion of seed germination.

Question 43

commercially applied gibberellins can relieve certain types of dormancy, including

Answer 43

nondeep and intermediate physiological dormancy, photodormancy, and thermodormancy.

Question 44

Do cytokinin or auxin have a major role in seed germination?

Answer 44

Cytokinin activity is important in early developing fruits and seeds but decreases in mature seeds. Auxin does not appear to play a major role in seed dormancy.

Question 45

What are karrikins?

Answer 45

KAR1 action requires gibberellin biosynthesis and stimulates germination through an interaction with ABA and gibberellin. Interestingly, it is also effective in stimu-lating germination in parasitic weed species. imitates smoke enhanced germination.