PLT 132 Plant Propagation

Seeds – part 3: Seed Technology D. W. Still

dwstill@csupomona.edu

Seeds – Part 3 Chapters 6 & 7

1. Harvesting and Processing Seeds

a.) Standard germination test (% normal seedlings) b.) Excised embryo test (woody plants, dormant seeds) c.) tetrazolium test (measures respiration – i.e., viability) d.) vigor test - “seed vigor comprises those seed properties which determine the potential for rapid, uniform emergence and development of normal seedlings under a wide variety of field conditions”. - includes accelerated aging, controlled deterioration, cold test, cool test, electrolyte leakage, seedling growth rate, high temperature tests, light tests, etc.

2. All (commercial) seeds will be tested

a.) All seeds must be collected, dried, cleaned, and stored. b.) Fleshy fruits (watermelon) or dry (lettuce, maize, etc.)

Seeds – Part 3

4. Seeds must be stored: a.) Orthodox vs. recalcitrant b.) Moisture content and temperature are key components. - vigor > normal germination > viability c.) Seeds are genetic resources.

3. Seed treatments serve several purposes: a.) Seed protectants: chemical trts, heat trts, innoculation. b.) Aid in planting: pellets, film coating. (Figs. 6-18, -19) c.) Aid in germination under stress: Priming

National Center for Genetic Resources Conservation – Ft. Collins CO

ca. 1958

Cryopreservation in liquid N2

“Noah’s Ark” Svalbard Global Seed Vault, Norway 26 February 2008

http://news.nationalgeographic.com/news/2008/02/photogalleries/seedvault-pictures/index.html

Seeds – Part 3

1. Seed transition from seed development to germination

a.) Germination with respect to water uptake (see figure 7.3)

Phase

II III I

Wat

er u

ptak

e

Time

Lag

Seeds – Part 3

1. All seed germination is based on water relations

i.) Matric potential = ψm

ii.) Osmotic potential = ψπ

iv.) ψcell = ψm + ψπ + ψp

a.) Water potential = ψcell

iii.) Pressure potential = ψp

Seeds – Part 3

GA

Adapted from Ni and Bradford 1993, Plant Physiology101:607- 617 See Figure 7-6

Seeds – Part 3

b.) Priming i) alleviate thermo- and photo-dormancy

1. Environment affects seed germination

c.) Water potential i) Embryo must generate force

a.) Temperature i) Max, min, optimum

b.) Light i) red light promotes, far-red or dark inhibits

Seed Technology

• Pelleted or coated seeds – Coating (diatomaceous earth) – Binding (inert materials)

• Change size and shape of seeds – Uniform size

• Precision planting (tractors)

Pelleted lettuce seed

Seeds – Part 3

b.) Primary: dormancy that is initiated during seed development

1. Dormancy

a.) definition: the inability of a seed to germinate when environmental conditions are favorable for germination to occur.

i. Exogenous – external to embryo ii. Endogenous – embryo specific

Seeds – Part 3

1. Dormancy

b.) Primary: dormancy that is initiated during seed development

i. Exogenous 1) Physical – e.g., seed coat, fruit parts Scarification may be needed

2) Chemical – chemicals produced by seed or fruit Leaching may be needed

ii. Endogenous

A) non-deep, intermediate, deep 2) Physiological – including: 1) Morphological – embryo is not fully developed

B) e.g., photodormancy, after-ripening, stratification

Seeds – Part 3

1. Dormancy

b. Secondary dormancy – seeds may lose primary dormancy and subsequently re-enter dormancy again. This is secondary dormancy.

i. Thermodormancy – seeds exposed to high temperatures fail to germinate when returned to a permissible temperature.

2. Release from dormancy

a. Hormonal balance is key to germination

b. GA promotes germination, ABA prevents germination

Seeds – Part 3

http://www.psy.ritsumei.ac.jp/~akitaoka/sun.jpg

Red light (660 nm)

Pr

Pfr

Seeds – Part 3

Filtered light (far-red) 730 nm

Pfr

Pr

18

X

F1

Recombinant inbred line (RIL) ‘Diplomat’ (Iceberg) X ‘Margarita’ (Butter)

Improvement of germination in lettuce through genetics and breeding

19

Recombinant Inbred Line (RIL) F1

F3

….. ….. ….. …..

F4

….. ….. ….. …..

F5

….. ….. ….. …..

F6

….. ….. ….. …..

F7

….. ….. ….. ….. Single seed descent

RIL population with 131 families (Dip x Mar)

F2 ….. ….. ….. …..

F8

0

10

20

30

40

50

60

70

80

90

100

178.2 24

311

6.2 139

218

177 88 10

118

9 83 173

124 92 16

324

022

1 410

.3 55 81 244 65 18

822

220

2 41 43 3D 89 130

138

217.2 11

119

4 28 93 12 193 3L 23

314

.1 54

Family Number

Fina

l ger

min

atio

n (%

)

Distribution of germination response after exposure to FR-D among RIL (D X M)

Dormant

Non-dormant

Far-red light can induce dormancy of lettuce seeds. Ability to germinate in FR24-D environment is a complex (quantitative trait).

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4

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11.0

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8

(Hayashi et al. 2008)

Determining the location of the genes that confer ability to germinate

Genetic mapping

Chromosome DNA markers

QTL

- what is the role of genes known to be involved in germination?

Profiling the expression of genes

Introgression of alleles from wild species improves high temperature germination in lettuce

Using traditional plant breeding techniques aided by marker assisted selection, beneficial genes can be

transferred to elite cultivars to improve traits

Gene tagged with a fluorescent protein identifies the location of the introgressed gene that will improve performance