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FIELD CROP > Seeds and Germination > Flashcards

Seeds and Germination Flashcards

1
Q

Double fertilization

A

Product of fertilization of egg in ovule; results from fusion of sperm nuclei w/egg cell and polar nuclei.

  • one sperm nucleus fuses w/2 polar nuclei –> 3n endosperm
  • one sperm nucleus fuses w/egg –> embryo (2n)
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2
Q

Function of seed coat

A

protection

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3
Q

function of embryo

A

seedling plant

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4
Q

function of endosperm and/or cotyedon

A

stored food to support seedling growth

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5
Q

function of enzymes and hormones

A

digest stored food to create energy and control cell division and development

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6
Q

carbohydrates include

A

starches, pentosans, mucilages

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7
Q

starches include

A

amylase and amylopectin

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8
Q

amylose

A

long chain glucose polymers. 100% digestible by amylase, makes up starchy endosperm

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9
Q

amylopectin

A

glucose polymers with side glucose chains, only 50% digestible by amylase, makes up waxy endosperm

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10
Q

pentosans

A

strongly imbibe water, found in coats of certain seeds

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11
Q

mucilages

A

polyuromides and galactomides, become sticky when wet

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12
Q

Lipids include

A

oils, fats, waxes

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13
Q

oils

A

Liquid at normal temps: principal energy storage in many species; frequently found in starchy seeds; seeds high in oil tend to be high in protein
Typically high in unsaturated fatty acids: degree of unsaturation relates to # of double bonds

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14
Q

fats

A

Typically solid at normal temps.

Generally higher in saturation (fewer double bonds)

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15
Q

waxes

A

Esters off fatty acids and a monohydric alcohol

In seed coats

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16
Q

Proteins include

A

albumins, globulins, glutelins, prolamins

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17
Q

Albumins

A

water soluble; includes enzymes; coagulate at high temp

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18
Q

Globulins

A

Soluble in water and salt solutions; do not readily coagulate with heating; Legumes are high in globulins (gycinin in soybean)

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19
Q

Glutelins

A

Insoluble in water but soluble in salt, acid, and alkali.

Bread wheats contain glutenin

20
Q

Prolamins

A

Soluble in alcohol
Good source of N to seedlings
Zein in corn, gliadin in wheat, and hordenin in barley

21
Q

Other seed compounds

A

phytin, alkaloids, phenolics

22
Q

Phytin

A

Primary source of P to germination seedling.

Released by enzyme phytase from aleurone layer

23
Q

Alkaloids

A

Cyclic Nitrogenous storage compounds.
Include caffeine, nicotine, morphine strychnine, etc.
Can serve as allelochemicals

24
Q

Phenolics

A

also called actones.
Include tannins, courmarin, caffeic acid, etc.
Can serve as dormancy mechanism by inhibiting

25
Q

Five requirements for germination

A
  1. Germinable seed
  2. Moisture
  3. Adequate temp
  4. Oxygen
  5. Light
26
Q

Nine steps in germination process

A
  1. Inhibition of water
  2. Hydration of tissues
  3. Absorption of O2
  4. Enzyme activation
  5. Digestion of stored food reserves
  6. Transport of hydrolyzed reserves to embryo
  7. Increase in respiration
  8. Cell division and enlargement
  9. Embryo emergence
27
Q

What hormones are involved in germination and what does each hormone do?

A
  1. Gibberellins: activate hydrolytic digestive enzymes
  2. Cytokinins: stimulate cell division in the embryo
  3. Auxins: promote growth through enlargement of coleohiza, radicle and plumule; activate geotropism (grows to the earth; responds to gravity)
28
Q

What enzymes are involved in germination and what does each do?

A
  1. Hydrolases- hydrolyze cell contents into constituent parts
    - Proteases
    - Lipases
    - Amylase
  2. Nucleases- help dissolve cell membranes
29
Q

Dormancy

A

when viable seeds do not germinate even though conditions are favorable

30
Q

What are the four causes of dormancy?

A
  1. immature embryo
    - found in orchidaceae, witchweed
  2. impermeable seed coat
    - impermeable to water, e.g. clovers
    - impermeable to O2; e.g. wild oats
  3. mechanical resistance
    - imbibe water, but resist embryo emergence, e.g. nuts
  4. physiological or embryo dormancy
    - requires after ripening to overcome hormone imbalance
31
Q

What methods can be used to overcome dormancy

A

scarification, stratification, leaching

32
Q

Scarification

A

scratch the seed coat mechanically or chemically

- allow water and oxygen to enter

33
Q

stratification

A

place seeds in moist, cool or cold environment

34
Q

leaching

A

wash with fresh water for 12-48 hrs to remove inhibitors in seed coat

35
Q

What factors affect seed quality?

A
  1. conditions during fill
  2. seed storage conditions
    - moisture content
    - storage environment
    > temp 0-32 degrees F idea; 32-50 degrees F adequate
    > relative humidity of 50-60%
    > reduced O2 concentration
  3. length of storage
36
Q

Seed purity

A

percentage of pure seed

37
Q

possible contaminants for seed purity

A 
seed of other crops.
Weed seed
  - Primary noxious weeds (prohibited) 
  - Secondary noxious (restricted)
Insect matter
38
Q

Standard seed germination test

A

Min of 400 seeds, divided into 4 or more separate tests.
Petri dish test, rolled-towel test, etc
Seed sanwhiched between two layers of absorbent material
Placed in a germinator at optimum conditions
count # of seeds germinated

39
Q

Tetrazolium test- colorimetric test

A

Tetrazolium is coloress.
When reduced by H ions, it turns red (changes to formazan)
When viable seeds imbibe water, H ions are released as dehydrogenasses become active.
Viable seeds become red
Dead seeds remain colorless

40
Q

Calculation for % pure live seed

A

% PLS= % germination x % purity

41
Q

Hypogeal emergence

A

cotyledon(s) stay below the surface (better)

42
Q

Epigeal emergence

A

Cotyledons emerge above the soil surface

43
Q

Describe the soil qualities important for good seedbed

A
  1. well-drained: if too wet, the seeds rot
  2. well aerated: provide O
  3. good water holding capacity: provide adequate moisture
  4. good tilth: good seed-soil contact
  5. no crusting- crusting impedes emergence
44
Q

What factors affect depth of seedling

A
  1. seed size: larger seeds have more food reserves and can emerge from deeper depths
  2. Type of emergence: plants w/ epigea emergence need to emerge above soil to commence seedling growth
  3. Soil type: heavy soil- seed shallower; light sandy soil- seed deeper
  4. Depth of available soil moisture: related to soil type
45
Q

List ad describe the factors to be considered when determining seeding rate

A
  1. Percentage of pure live seed
  2. Plant’s capacity for competition
    -large plants need more room
    - indetermindate cutivars need more space than determinate
    > Determinate will grow to certain point then stop and flower
    > Indeterminate will continue to grow but flower anytime
  3. Cultural conditions
    - fertility levels
    - irrigation: higher seeding rates when crop will be irrigated (up to double the rate)
    - time of planting- plant at optimum time
    -row spacing
46
Q

list and describe the factors that affect crop stand

A
  1. Plant factors
    - adapted to region, high genetic purity, free from contaminatns
  2. environmental factors
    - adequate water, temp, oxygen, and proper light or dark conditons
  3. management factors
    - sow seeds at proper time, at proper depth; well-prepared seed-bed; protect from disease, insects, and weeds

FIELD CROP (10 decks)

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