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Fundamentals of Seed Production I: Genetics, Breeding, and Seed Production

Samuel Contreras Pontificia Universidad Católica de Chile Departamento de Ciencias Vegetales Santiago - Chile

I- INTRODUCTION

· Food, feed, and fiber production, fundamental goal of agriculture.

Inhabitants x 10 10 8 6 4 2 0 1300 1400 1500 1600 1700 Year 1800 1900 2000

9

How to deal with the increasing demand? · New technologies for yield improvement:

­ ­ ­ ­ ­ ­ ­ Development of new cultivars (breeding) Establishment techniques Watering Nutrient supply Crop protection Post harvest etc.

World Population

2050: 9 x 109

2015: 7.15 x 109 2000: 6 x 109 1900: 1.7 x 109

Breeding, main objectives How to deal with the increasing demand? · New technologies for yield improvement:

­ ­ ­ ­ ­ ­ ­ Development of new cultivars (breeding) Establishment techniques Watering Nutrient supply Crop protection Post harvest etc.

50%

Maize yield in bushels per acre in the United States. The periods dominated by openpollinated, and double and single crosses hybrids are indicated along with regression coefficients (from Crow, 1998).

Other common objectives of breeding during the last 50 years (Fehr, 1987):

­ ­ ­ ­ ­ ­ ­ Disease and insect resistance Seed composition Forage quality Tolerance to environmental stresses Adaptability to mechanization Lodging resistance Photoperiod response

New tendencies in breeding objectives:

­ Quality traits ­ Accumulation or "stacking" of traits ­ New uses: · Ornamental and recreational · Medicinal · Industrial (biopolymers, biofuels)

Impact of biotechnology on plant breeding

· Seed has become a delivery mechanism for new technologies and a high value products

Activities involved in seed production:

ACTIVITY Genetic Selection Seed Production Seed Collection OBJECTIVES Develop superior varieties High yield of genetically pure seed with high performance Maximize yield at optimum stage of development for quality seeds Separate seed from fruit and remove non-seed material and weed seeds Enhance seed germination or facilitate sowing Retain seed quality until sale to or use by crop producer

Attributes of genetically pure seed (Kester et al 1997): · Trueness to name · Trueness to type · Freedom from contaminants

Seed Conditioning Seed Treatments Packaging and Storage

(from Kester et al 1997)

· In general, the objective of any propagation technique is to multiply a specific genotype and produce the kind of plant or phenotype that we are interested.

II- GENETICS OF PLANT POPULATIONS AND BREEDING SYSTEMS

· In general, the objective of any propagation technique is to multiply a specific genotype and produce the kind of plant or phenotype that we are interested.

· In general, the objective of any propagation technique is to multiply a specific genotype and produce the kind of plant or phenotype that we are interested.

Genotype

(genetic constitution)

Genotype

(genetic constitution)

Phenotype

(external appearance)

· In general, the objective of any propagation technique is to multiply a specific genotype and produce the kind of plant or phenotype that we are interested.

Environment C

Environment A Environment A Genotype Genotype

(genetic constitution)

Phenotype

(external appearance)

(genetic constitution)

Environment B

Genotype x Environment = Phenotype

X

X

Genotype

X chromosome genes

Homologous chromosome

Homologous chromosomes:

a1

Homologous chromosomes:

a1

locus

a2

· Genes at the same locus affect the same trait and are called alleles

locus

a2

· Genes at the same locus affect the same trait and are called alleles Supposing there is not dominance: a1 & a1 = a1 & a2 = a2 & a2 =

Homologous chromosomes:

a1

Homologous chromosomes:

a1

locus

a2

· Genes at the same locus affect the same trait and are called alleles If a1 is dominant and a2 is recessive: a1 & a1 = a1 & a2 = a2 & a2 =

Locus a

a2

b1 c1

b1 c3

Locus b is homozygous Locus c is heterozygous

Homozygous genotype

Homozygous genotype

Heterozygous genotype

Homozygosis and self-pollination

Homozygous genotype

Homozygosis and self-pollination

Gametes Homozygous genotype

(pollen or ovule)

Homozygosis and self-pollination

Gametes Homozygous genotype

(pollen or ovule)

Progeny

Effect of self-pollination and roguing following crossing of a Tall (DD) and Dwarf (dd) pea. Fixing of the two parental phenotypes can be observed in succeeding generations in the proportion of tall and dwarf plants. Continuous roguing for the recessive trait never eliminates totally its segregation from residual heterozygous individuals (Kester et al 1997) Continuing selfpollination proportions DD Dd dd Roguing of all dwarfed plants Tall Dwarf %dd

Percent homozygous

P1 F1 F2 F3 F4 F5 F6 F7

1 1 3 7 15 31 126 1 2 2 2 2 2 2

1 1 3 7 15 31 126

100 0 50 75 87.5 93.75 96.88 98.44

All 3 14 35 143 535 2143

1 1 1 1 1 1

25 7.1 2.8 0.7 0.2 0.05

Effect of self-pollination and roguing following crossing of a Tall (DD) and Dwarf (dd) pea. Fixing of the two parental phenotypes can be observed in succeeding generations in the proportion of tall and dwarf plants. Continuous roguing for the recessive trait never eliminates totally its segregation from residual heterozygous individuals (Kester et al 1997) Continuing selfpollination proportions DD Dd DD x dd dd Roguing of all dwarfed plants Tall Dwarf %dd

Effect of self-pollination and roguing following crossing of a Tall (DD) and Dwarf (dd) pea. Fixing of the two parental phenotypes can be observed in succeeding generations in the proportion of tall and dwarf plants. Continuous roguing for the recessive trait never eliminates totally its segregation from residual heterozygous individuals (Kester et al 1997) Continuing selfpollination proportions DD Dd dd Roguing of all dwarfed plants Tall Dwarf %dd

Percent homozygous

Percent homozygous

P1 F1 F2 F3 F4 F5 F6 F7

1 1 3 7 15 31 126

1

1 (100% Dd) 2 1 2 3 2 2 2 2 7 15 31 126

100 0 50 75 87.5 93.75 96.88 98.44

All 3 14 35 143 535 2143

1 1 1 1 1 1

25 7.1 2.8 0.7 0.2 0.05

P1 F1 F2 F3 F4 F5 F6 F7

1 1 25% DD 3 7 15 31 126 1 2 50% Dd 2 2 2 2 2

1 1 25% dd 3 7 15 31 126

100 0 50 75 87.5 93.75 96.88 98.44

All 3 14 35 143 535 2143

1 1 1 1 1 1

25 7.1 2.8 0.7 0.2 0.05

Effect of self-pollination and roguing following crossing of a Tall (DD) and Dwarf (dd) pea. Fixing of the two parental phenotypes can be observed in succeeding generations in the proportion of tall and dwarf plants. Continuous roguing for the recessive trait never eliminates totally its segregation from residual heterozygous individuals (Kester et al 1997) Continuing selfpollination proportions DD Dd dd Roguing of all dwarfed plants Tall Dwarf %dd

Gametes Homozygous cultivar

(pollen or ovule)

Progeny from Self-pollination

Percent homozygous

P1 F1 F2 F3 F4 F5 F6 F7

1 1 3 7 15 31 126 1 2 2 2 2 2 2

1 1 3 7 15 31 126

100 0 50 75 87.5 93.75 96.88 98.44

+

All 3 14 35 143 535 2143

1 1 1 1 1 1

25 7.1 2.8 0.7 0.2 0.05

Pollen flow and contamination risk

isolation

Pollen flow and contamination risk

Seed production area Seed production area

Roguing: elimination of off-type plants

Off-type plant

Roguing: elimination of off-type plants

Off-type plant

Seed production area

Seed production area

Heterozygosis and cross-pollination

Heterozygous genotype

Heterozygosis and cross-pollination

Heterozygous genotype Gametes

(pollen or ovule)

Heterozygosis and cross-pollination

Heterozygous genotype Gametes

(pollen or ovule)

Asexual propagation

Sweet potato root

Progeny

Artichoke rooted sucker Garlic cloves (bulb) Potato tuber

Asexual propagation

Progeny (clones) Heterozygous genotype

Open pollinated seed production

Breeding

Asexual propagation Heterozygous population Selected cultivar

Open pollinated seed production

Hybrid seed production

Seed production: ·Isolation ·Roguing

Selected cultivar

Progeny from OP seed

Heterozygous population

Enforced selfpollination of selected individual through several generations

Inbred line

·Homozygous genotype ·High uniformity ·Low vigor (inbreed depression)

Hybrid seed production

Gametes Line A

Hybrid seed production

Gametes Line A

Hybrid cultivar

Line B

Line B

H y b r i d i z a t i o n

·Heterozygous genotype ·Very uniform ·Vigorous (heterosis)

Hybrid seed production

· An hybrid cultivar may be defined as the first generation from a cross that results from controlled pollination between progenitors with different genotype. The seed obtained from that cross is the only commercial seed that may be designated as hybrid.

Comparison of grain yields for hybrid maize and their inbred parents from different decades of use when grown in the same environment (from Fehr, 1987).

A

AxB

B

AxB A B AxB

(AxB)xC

C

Single-cross hybrid, from the cross between two inbred lines (A and B in this figure).

Three-way cross hybrid, from the cross between a single-cross hybrid (AxB) and an inbred line (C).

A

AxB

B

C

CxD

D

DxA

(AxB)x(CxD)

D

A

AxB

CxD

Double-cross hybrid, from the cross between two single-cross hybrid (AxB and CxD).

Top-cross hybrid, from the cross between an inbred two inbred line (A) and an open-pollinated cultivar (D)

Apomixis

· Involves seeds, but is an asexual form of reproduction · Progeny is genetically identical to mother plant · Facultative apomixis: sexual and apomictic seeds are produced · Obligate apomixis: all seeds formed are apomictic

III- MECHANISMS FAVORING SELF- OR CROSS- POLLINATION

In sexual reproduction, seeds are classified according with the source of pollen that is responsible for fertilization (Fehr, 1987): · Self-pollinated seeds are formed when the pollen is produced on the same plant as the ovule which it fertilizes. · Cross-pollinated seeds result when the pollen of one plant fertilizes the ovule of another plant.

Types of plant species according with frequency of self- or crosspollination (Fehr, 1987): · Self-pollinated or autogamous · Cross-pollinated or allogamous

Perfect or hermaphroditic flowers:

Perfect or hermaphroditic flowers:

Imperfect or unisexual flowers:

Modifications of perfect flowers that may favor either self- or cross-pollination:

Mechanism Favoring self-pollination Cleistogamy Homogamy Production of closed flowers Simultaneous maturation of male and female structures Description

Self-pollination in lettuce:

Corolla Stigma Pollen Stamens

Favoring cross-pollination Chasmogamy Dichogamy Protandry Protogeny Self-incompatibility Sterility Heterostyly Pollination occurs in open flowers Stamens and stigma mature at different moments pollen shed before the stigma is receptive stigma matures and cease to be receptive before pollen shed Inability to self-pollinate Production of non-functional gametes or sexual structures Two or more different positional arrangements of anthers and stigma

Ovary

Emergence of style and stigma through staminal column in lettuce perfect flowers (from Besnier, 1989)

Protogyny in magnolia:

Heterostyly in primula:

thrum plant

pin plant

In the first day flower, the stigmas are receptive and the anthers have not begun to shed pollen. In the second day flower, the anthers are shedding pollen and the stigmas are no longer receptive. This example is Magnolia grandiflora, southern magnolia.

Photos taken by K. R. Robertson of trees at the University of North Carolina. http://www.life.uiuc.edu/plantbio/digitalflowers/index.htm

From Silverside, 2002, at: http://www-biol.paisley.ac.uk/bioref/Genetics/Primula_heterostyly.html

Heterostyly in primula:

stigma

Heterostyly in primula:

anthers

stigma

thrum plant

pin plant

thrum plant

pin plant

From Silverside, 2002, at: http://www-biol.paisley.ac.uk/bioref/Genetics/Primula_heterostyly.html

From Silverside, 2002, at: http://www-biol.paisley.ac.uk/bioref/Genetics/Primula_heterostyly.html

Heterostyly in primula:

Self-incompatibility

Self-incompatibility is the inability of functional pollen to set seed after self-pollination.

thrum plant

pin plant

Two types: · Gametophytic self-incompatibility · Sporophytic self-incompatibility

From Silverside, 2002, at: http://www-biol.paisley.ac.uk/bioref/Genetics/Primula_heterostyly.html

Gametophytic self-incompatibility

Gametophytic self-incompatibility results from the interaction between the haploid genotype of the pollen grain and the diploid genotype of the pistil.

Gametophytic self-incompatibility

Gametophytic self-incompatibility results from the interaction between the haploid genotype of the pollen grain and the diploid genotype of the pistil.

Aborted pollen tube

normal pollen tube

Example of gemetophytic self-incompatibility with three alleles (S1, S2, and S3). Results from the pollinization with pollen S1 and S2 and pistils S1S2, S1S3, and S2S3. Only S2S3 and S1S3 zygotes are formed (from Besnier, 1989).

Gametophytic self-incompatibility

Relations of compatibility and incompatibility for a population with three alleles "S" for the locus of self-incompatibility.

Plant Plant S1 Pistil S1S2 Pistil S1S3 Pistil S2S3 Pollen S1S2 S2 S1 Pollen S1S3 S3 S2 Pollen S2S3 S3

Sporophytic self-incompatibility

Sporophytic self-incompatibility results from the interaction between the diploid genotype of the pollen grain and the diploid genotype of the pistil.

+

+ -

+

+ -

+ -

+ -

+: compatible - : non-compatible

Sporophytic self-incompatibility

Sporophytic self-incompatibility results from the interaction between the diploid genotype of the pollen grain and the diploid genotype of the pistil.

Diploid genotype pollen grain

Sporophytic self-incompatibility

Types of sporophytic self-incompatibility in relation with the dominance of the incompatibility alleles in pollen and pistil in cruciferae species (Besnier 1989).

Type

Polen Dominance Dominance

Pistil Independence Independence

Group of species where this type of incompatibility may be found cabbage, brussels sprouts cabbage, brussels sprouts, broccoli, chineese cabbage, kohlrabi, rabano cabbage chineese cabbage, kohlrabi, rabano

I II III IV

(from Kester et al 1997)

Diploid genotype pistil

Example of sporophytic self-incompatibility with four independent alleles (S1, S2, S3, and S4). Results from the pollinization with pollen S1S2 and pistils S1S2, S2S3, and S3S4. Only genotypes without common alleles are compatible.

Independence Dominance Independence Dominance

Male Sterility

Male sterility is the failure of a plant to produce functional pollen. Two types: · Genetic male sterility · Cytoplasmic male sterility

Genetic male sterility

Three possible genotypes:

ms ms

Homozygous, male sterile

Ms ms

Heterozygous, male fertile

Ms Ms

Homozygous, male fertile

Genetic male sterility

Hybrid seed production using genetic male sterility:

Pollen receptor line

ms ms

Cytoplasmic male sterility

ms ms

Pollen donor line X

Ms Ms

S

sterile cytoplasm (S) + homozygous genotype for ms = male sterile

ms ms

N

Ms ms Ms ms

normal cytoplasm (N) + homozygous genotype for ms = male fertile

S

sterile cytoplasm (S) + heterozygous genotype = male fertile

Hybrid cultivar

S

Ms Ms

sterile cytoplasm (S) + homozygous genotype for MS = male fertile

Cytoplasmic male sterility

Hybrid seed production using cytoplasmic male sterility:

Pollen receptor line

rf rf

Pollen donor line X N

Rf Rf

S

S

Rf rf

Hybrid

Information

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