This document discusses plant breeding and propagation. It begins with an overview of crop plant evolution, noting that six plant species provide 80% of calories consumed by humans. Plant breeding is described as accelerated evolution guided by humans to modify plant genetics, with the goal of improving traits like yield. Breeding methods include pure-line selection, mass selection, and creating hybrids. The document also covers plant propagation through seeds, asexual methods like cuttings and grafting, and micropropagation.

1. Plant Breeding and
Propagation
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2. Outline
 Crop Plant Evolution
 Plant Breeding
• Breeding Methods Using Sexually Compatible
Germplasm
• Breeding Methods Using Sexually Incompatible
Germplasm
 Plant Propagation
• Seed Propagation
• Asexual Plant Propagation

3. Crop Plant Evolution
 Approximately 250,000 living species of flowering
plants
• Six species provide 80% of calories consumed by
humans worldwide.
– Wheat, rice, corn, potato, sweet potato, and cassava
• Eight additional plants complete list of major crops
grown for human consumption.
– Sugar cane, sugar beet, bean, soybean, barley, sorghum,
coconut, and banana
 Plants domesticated by altering them genetically.
• Domesticated plant - Reproductive success depends
on human intervention.
• Ongoing evolutionary process

4. Crop Plant Evolution
Origins of Agriculture
 Agricultural practices arose independently in
many parts of world.
 People began to domesticate plants in Near East
(Iran) around 10,000 years ago.
• Domestication in Asia and New World 1,000 to 3,000
years later
 First crops were cereal grains.
• Root crops and legumes domesticated 1,000 to 2,000
years later.
• Followed by vegetables, then oil, fiber and fruit crops
• Plants for forage, decoration, and drugs first
domesticated about 2,000 years ago.

5. Crop Plant Evolution
Origins of Agriculture
Regions of domestication

6. Plant Breeding
 Plant breeding is accelerated evolution guided
by humans rather than nature.
• Breeders replace natural selection with human
selection to modify plant genetics.
– Primary goal of plant-
breeding programs is
improved yield, with disease
resistance, pest resistance,
and stress tolerance
contributing to yield.
 Genetic variation provides
foundation for improving
plants through breeding.
Potato tuber diversity

7. Plant Breeding
Breeding Methods Using Sexually Compatible Germplasm
 Strategies
• Self-pollinating plant - Capable of fertilizing itself
– Tend to be highly homogeneous - Genes come from
same parent.
o Significant inbreeding
« Wheat, rice, oats, barley, peas, tomatoes,
peppers, some fruit trees: apricots, nectarines,
citrus
– Pure-line selection:
o Seeds collected from several plants.
o Seeds from individual plant grown in same row.
o Most desirable row selected.

8. Plant Breeding
Breeding Methods Using Sexually Compatible Germplasm
 Strategies
• Cross-pollinating plant - Must be fertilized from
other individuals
– Tend to be highly heterozygous
o Corn, rye, alfalfa, clover and most fruit, nuts and
vegetables
– Mass selection - Many plants from a population
selected, and seeds from these plants used to create
next generation.
o Seeds from the best plants chosen and propagated,
for many generations.

9. Plant Breeding
Breeding Methods Using Sexually Compatible Germplasm
 Strategies
• Outcrossing in cross-pollinated crops often results
in hybrid vigor (heterosis).
• Self pollination of cross-pollinating plants results in
inbreeding depression.
– Due to expression of deleterious recessive alleles
– Modern breeders force self-pollination in cross-pollinated
species to create inbred lines in which deleterious alleles
eliminated.
o Selected inbred lines crossed to produce hybrid seed.
« Successful in corn
– Heirloom varieties grown as open-pollinated populations.
« Genetic variability allows crop production under
different environmental conditions.

10. Plant Breeding
Breeding Methods Using Sexually Compatible Germplasm
 Impossible to improve population if there is
no genetic variability for trait.
 Germplasm - Sum total of a plant’s genes
• Current agricultural varieties are often genetically
uniform, and thus may not be good sources of
new genetic variability.
– Homogeneity makes them vulnerable to pest outbreaks.
• Gene banks established to meet current and
future demands of plant genetic diversity.
– Seeds or other propagules put into long-term storage.

11. Plant Breeding
Breeding Methods Using Sexually Incompatible Germplasm
 Using sexually incompatible germplasm -
Across species boundaries
 Protoplast fusion
• Cells of each species grown in liquid nutrient
solution.
• Cell walls chemically stripped to produce protoplasts.
• Protoplasts of two species mixed together and
stimulated, with aid of an electric current or chemical
solution, to fuse with each other.
• Grow hybrid fusions by tissue culture.
– Form somatic hybrids - New plants that carry genes from
two distantly related species
– Few successes

12.  Transgenic plants - Produced by inserting
genes from virtually any organism into plants
Plant Breeding
Breeding Methods Using Sexually Incompatible Germplasm
• Recombinant DNA
technology used.
– Restriction enzymes
from bacteria cut DNA
into fragments with
one DNA strand
longer than other,
creating sticky ends.
o Sticky ends base-
pair with tail of other
fragments cut with
same enzyme.

13.  Transgenic plants
• Plasmids commonly used as cloning vectors.
– Plasmid - Small circular bacterial DNA capable of
independent replication
• To clone gene:
– A bacteria plasmid and a gene of interest from foreign
DNA cut by restriction enzymes.
– Gene becomes inserted into plasmid.
– Transformation - Bacteria, Escherichia coli, stimulated to
take up plasmid.
– Bacteria multiply.
Plant Breeding
Breeding Methods Using Sexually Incompatible Germplasm

14. • To clone gene:
Plant Breeding
Breeding Methods Using Sexually Incompatible Germplasm

15.  After cloning, gene inserted into plant cells via
transformation:
• Plasmids removed from E. coli.
• Same restriction enzymes used to cut out gene.
• Plant is transformed with new gene.
– Two techniques used:
o Agrobacterium tumefaciens used to insert transfer DNA
(T-DNA) that contains gene of interest from its plasmids
into plant’s chromosomes.
o Particle guns - Shoot DNA into plant tissue
« Tungsten or gold pellets coated with cloned gene shot
into plant cells.
« Process of how this works is a mystery.
Plant Breeding
Breeding Methods Using Sexually Incompatible Germplasm

16.  Transformation of plant by Agrobacterium
tumefaciens:
Plant Breeding
Breeding Methods Using Sexually Incompatible Germplasm

17.  Steps in making a transgenic plant:
Plant Breeding
Breeding Methods Using Sexually Incompatible Germplasm

18.  Pros of transgenic plants
• Transgenic crops environmentally friendly.
– Farmers can use fewer and less noxious chemicals for
crop production.
 Cons of transgenic plants
• Unanswered questions need to be answered:
– Effects on non-target organisms, such as beneficial insects,
worms or birds?
– Effects on humans eating transgenic crops?
o Allergic reaction to transgene protein product?
– Movement of herbicide-resistance genes into weeds?
– Evolution of insects to be able to eat transgenic plants?
– Encouragement of farmers to head farther away from
sustainable agricultural farming.
Plant Breeding
Breeding Methods Using Sexually Incompatible Germplasm

19. Plant Propagation
Seed Propagation
 Hybrid varieties often grown from seed
produced by crosses between two inbred
parents.
• Produce highly variable population
• Corn
 Inbred line varieties typically grown from
seed and allowed to self-pollinate.
• Produce plants nearly identical to parents

20. Plant Propagation
Seed Propagation
 Mature seeds harvested and stored in a
controlled environment.
• Viability best when seeds maintained in cool, dry
storage.
 In preparation for planting, seeds dusted
with a protectant, such as fungicide.
 Seeds planted in a suitable bed.
• Moist soil to allow seeds to imbibe water
• Dry enough to maintain suitable oxygen levels

21. Plant Propagation
Asexual Plant Propagation
 Asexual propagation - Uses vegetative parts
 Crown division - Plant separated into several
pieces, each with crown portion and roots.
Crown division
of daylily

22. Plant Propagation
Asexual Plant Propagation
 Cuttings - Propagation from parts of plants
• If stem used, produces adventitious roots.
– Cells near the wound must dedifferentiate and create a
new meristematic region.
– Sometimes rooting is stimulated by auxin.
• Identical copies of
valuable plants
can be made.
• Disadvantage -
Diseases carried
by mother plant
propagated.

23. Plant Propagation
Asexual Plant Propagation
 Layering
• Works well for some
plants that are not easy
to propagate by cuttings.
• Tip layering - Tips bent
until touch ground, and
then covered with soil.
– Roots form on buried stem.
– Blackberries, boysenberries
• Air layering - Branch or main stem wounded or
girdled to produce roots.
– Tropical trees and shrubs
Tip layering

24. Plant Propagation
Asexual Plant Propagation
 Grafting - Segments of different
plants connected and induced to
grow together as one plant.
• Fruit and nut trees
• Scion - Top part of graft
• Rootstock - Bottom portion
– Selected for winter hardiness,
dwarfing and disease resistance
• Success depends on good contact
between vascular cambium of scion
and that of rootstock.

25. Plant Propagation
Asexual Plant Propagation
 Micropropagation - Grow and maintain plants
in a disease-free status in test tubes
• Advantages:
– Can grow large numbers of plants in small area.
– Minimal maintenance required.
– Rapid multiplication
• Grown in-vitro in sterile medium and maintained in
controlled environments
• Relies on totipotency of plant cells
– Totipotency - Capacity of a cell to give rise to any
structure of a mature organism

26. Plant Propagation
Asexual Plant Propagation
 Micropropagation begins with establishment of
explants in tissue culture.
• Explant - Excised piece of stem or leaf tissue
• Plant parts disinfested and inserted into growth
medium in test tubes.
• Induced to develop multiple shoots = microshoots
• Microshoots separated and placed in new medium by
subculturing.
• Roots induced by transferring to rooting medium.
• Plants transferred back to outdoor environment.

27. Review
 Crop Plant Evolution
 Plant Breeding
• Breeding Methods Using Sexually Compatible
Germplasm
• Breeding Methods Using Sexually Incompatible
Germplasm
 Plant Propagation
• Seed Propagation
• Asexual Plant Propagation