Selection%20and%20Management%20of%20Clones

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Chapter 16

• Selection and Management of Clones

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Selection and Management of Clones

• Vegetative propagation
• Goal produce progeny identical in genotype to a
  single source plant
• Cloning clones
• Occurs naturally
• Bulbs
• Rhizomes
• Runners
• Tip layers

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Selection and Management of Clones

• Clones not favored in nature
• Does not allow variation
• Does not allow evolutionary development
• Early vegetative prop.
• Potato - Grapes
• Yam - Olives
• Sugar cane - Figs
• Banana - Popular and Willow for fences

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Selection and Management of Clones

• Reasons for cloning
• Maintain superior genotypes
• Keep uniformity of crop
• Facilitate propagation
• Combine more than one genotype onto a single
  plant
• Control phases of development

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Selection and Management of Clones

• Fixing genotypes
• Unique characteristics would be lost in seed
  propagation
• Uniformity of crop
• Plant size, growth rate, flowering time
• Facilitate propagation
• unpredictable seed production
• Seedless plants (grapes, oranges, limes)

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Selection and Management of Clones

• Shorten time to flower
• Flower at an earlier age
• Clones are typically in mature phase of
  development
• Combo of 2 genotypes
• Grafting
• Why?
• Control plant height
• Scion does not root readily
• Add a pollinator branch to a self-incompatible
  cultivar
• Control phases of development
• Juvenile to mature (adult)

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Selection and Management of Clones

• Genetic basis of clones
• Cultivars come from seedling populations or
  mutations
• 1.) Seedling selection
• Multiple propagation from the same plant
• Consecutive generation of propagation
• So plant ortet (original selection)
• Ramets vegetatively propagated generation
• (a,b,c... Designates different parts of the ortet
  propagated)
• (S1 S2 S3 consecutive generations)

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Ortet-original selection
Ramets
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Selection and Management of Clones

• Genotype x Environment interactions can occur!
• Traits that vary in different locations
• Ex Malus domestica Delicious
• (discovered in 1870 in Iowa) East coast is
  rounded and West coast is elongated unless those
  on the East coast are chemically treated with GA
  so that they will elongate

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Selection and Management of Clones

• 2.) Mutations
• Chance mutations in an established clone
• Result from changes in the chromosomes
• Point mutations rearrangement in 1 of the 4
  bases in DNA (A,T,G,C)
• Deletions, duplications, translocations and
  inversions all result in rearrangement of parts
  of the chromosomes
• Aneuploidy addition of loss of individual
  chromosomes
• Polyploidy multiplication of entire sets of
  chromosomes

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Diploid Tetraploid
Tobacco
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Selection and Management of Clones

• Mutations can occur from UV light, X-rays, and
  chemicals
• Bud sport suddenly appearing mutation that
  grows and is conspicuous
• Ex Ruby Red grapefruit is a sport from
  regular grapefruit
• Variegated Clivia
• Variegated Peperomia
• Variegated Plectranthus
• Variegated Spiraea

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Plectranthus
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Selection and Management of Clones

• Created mutations
• Biotechnology introducing DNA fragments from
  one organism to another recombinant DNA
  technology

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Selection and Management of Clones

• Kinds of Genetic Variation within Clones
• Chimeras mutations the occur in a single cell
  of a clone and produce an island of mutant
  cells within the growing point of the stem

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Selection and Management of Clones

• Types of chimeras
• Periclinal mutated tissue occupies a layer of
  cells that completely surrounds an inner core of
  non-mutated tissue
• Ex Red-fruited apple (Red pigment only in
  epidermal layer)
• These chimeras are stable
• Propagation must include the shoot apex
• Not stable from adventitious buds (from root
  cuttings or tissue culture)

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Selection and Management of Clones

• Types of chimeras
• Mericlinal cells with mutant gene only occupy
  part of the outer cell layer
• Ex streaking on fruit, color bands
• This is unstable
• Sectorial mutated cells occupy an entire sector
  of the stem including all layers of the shoot
  apex
• Ex broad sectors on fruit that go deep into the
  fruit
• Unstable

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Selection and Management of Clones

• Transposons jumping genes
• Barbera McClintock - Nobel prize in 1984
• Different portions of the chromosomes turn on/off
• Transmitted to seedlings stable
• Ex Indian corn Jingle Bells poinsettia

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Selection and Management of Clones
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Selection and Management of Clones
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Selection and Management of Clones

• Origin of chimeras
• In meristem (dividing cells)
• In layers (histogens). Generally 3-4 layers
• L-I (outer) epidermis - division is
  perpendicular to the surface (anticlinal)
• L-II (middle) leaf margin stem cortex -
  division is usually anticlinal but sometimes
  periclinal (parallel to the surface). This will
  force cells into the L-1 layer
• L-III (inner) leaf core

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Selection and Management of Clones

• Mutation of L-I periclinal or mericlinal
  chimeras
• Mutation of L-II also affects the reproductive
  structures (flower and ovary) but not the seed
  inside. Therefore a mutation in this layer is not
  transmitted to the seed. Often results in a
  mericlinal chimera

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Selection and Management of Clones

• Ferns, gymnosperms and roots have unlayered
  meristems. Therefore, chimeras are sectorial.
  This can result in stable or unstable mutants.
• Layers are different for monocots and dicots

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Selection and Management of Clones

• Dicot GWG (Ex African violet)
• Monocot GWW (Ex Spider plant)

Leaf center
Epidermis clear
Leaf margin
Epidermis Leaf margin
Leaf center (some)
Leaf center
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African violets
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Selection and Management of Clones
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Spiderplants
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Selection and Management of Clones

• Maintaining stability of chimeras
• Periclinal relatively stable as long as the
  growing point has continuity with the shoot
  system of the source plant
• Stem cuttings
• Division
• Layering
• Scion
• Not good from root or leaf cuttings or
  adventitious shoots (from T.C.)

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Selection and Management of Clones

• Reversions of periclinal chimeras happen if L-II
  cells displace L-I cells.
• (Ex a solid green shoot develops on a
  variegated plant)
• Mericlinal sectorial chimeras can be completely
  unstable

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Reversions
Pinwheel phlox
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Reversions
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Reversions
Dwarf Alberta Spruce
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Reversions-
Peperomia
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Selection and Management of Clones

• Non-genetic variation within clones (epigenetic)
• Environmental effects on phenotype expression
• (Ex Delicious apples different on East and
  West coasts)
• Phase variation (change in maturation)
• Homoblastic - little obvious change in phenotype
  of seedling with age
• Heteroblastic - different parts of the plant
  exhibit distinct variation of specific traits
  with age (spines/thorns when juvenile and none
  when mature)
• Ex black locust and citrus

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Selection and Management of Clones

• Note the part of the plant nearest the base of
  the plant is oldest in terms of chronological
  age but actually is youngest (more juvenile) in
  terms of physiological maturity (ontogenetic age)
• Propagules from base of the plant biologically
  juvenile plants
• Propagules from the top of the plant
  biologically mature plants

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Selection and Management of Clones

• Promoting shifts from juvenile to mature phases
• To speed up maturation, keep plants in continuous
  growth (get through juvenile period more quickly)
• Maintenance of juvenile phase (for rooting)
• Collect material displaying juvenile
  characteristics
• Collect root sprouts (suckers) or force stump
  sprouts
• Establish hedge rows for severe pruning each
  year

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Selection and Management of Clones

• Reversion from mature to juvenile phase
• Easiest and quickest to start from seed!
• Adventitious shoots on roots
• Consecutive grafting onto seedling rootstock
• Consecutive subculturing of meristems in T.C.
• GA treatment (sometimes)
• Cuttings from the cone of juvenility

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Selection and Management of Clones

• Topophysis
• The effect of position of the propagule on the
  plant upon the type of vegetative growth
  subsequently displayed by the vegetative progeny
• Orthotropic upright cuttings vertical
  shoots
• Plagiotropic lateral cuttings horizontal
  shoots
• Happens mostly in conifers and some broadleaf
  evergreens!

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Coffee
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Holly
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Selection and Management of Clones

• Pathogens and Plant Propagation
• Systemic pathogens and clones
• Viruses - nucleic acids (either DNA or RNA)
  encased in a protein coat. Replicates in a plant
  cell. Transmitted by an insect vector or humans.
  Ex TMV
• Phytoplasm (mycoplasma-like organism MLOs).
• One celled parasite
• Lives in phloem and leaf hoppers
• Blocks phloem and causes a witchs broom

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Witchs broom in Pinus sylvestris
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Selection and Management of Clones

• Management of sources for vegetative propagation
• Trueness-to-name labeling, records
• Trueness-to-type characteristics of progeny.
  Protein analysis isozymes
• Freedom from pathogens
• Visual inspection (however, no symptom does not
  mean no pathogen)
• Culture indexing - surface sterilize plant part
  and culture pieces
• Virus indexing - graft/bud onto a sensitive
  indicator plant
• Serology - ID proteins using ELISA (enzyme-linked
  immuno-sorbent assay)

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Trueness-to-Type
Isozyme analysis
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Trueness-to-Type
RAPD (Randomly Amplified Polymorphic DNA)
profile of Apricot
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Culture Indexing
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Virus Indexing
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Virus Indexing
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Virus Indexing-Elisa
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Virus Indexing-Elisa
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Virus Indexing
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Selection and Management of Clones

• Elisa Purified extract of pathogen injected
  into a rabbit produces antibodies in the blood to
  react to viral proteins. These are extracted and
  put in a gel that lines the walls of well in a
  plate. The plant extract with possible virus is
  added to the wells. If the virus is present, it
  is bound to the antibodies lining the well and
  can be quantified spectrophotometrically.

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Selection and Management of Clones

• Now PCR (polymerase chain reaction) is being used
  and the resultant DNA sequenced. DNA sequences
  can be compared to pure DNA sequences of
  virus/bacteria/fungi and identified. It is
  difficult to quantify the amount of pathogen
  present in the plant using this technique.

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Selection and Management of Clones

• Treatments to eliminate pathogens from plants
• Select uninfected plant parts (not near soil)
• Shoot apex culture (meristems). Cells grow in
  advance of most pathogens (esp. viruses)
• Select only 0.1mm shoot tip
• Difficult to get established in T.C.
• Used with orchids, amaryllis, carnations, mums,
  geraniums, lilies, apples, bananas, citrus,
  grapes, strawberries and potato

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Meristem tip culture
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Selection and Management of Clones

• Heat treatment
• Vary with species (110-135F for 1/2 - 4 hours)
• Hot water best
• Thermotherapy
• Container-grown plants placed in 98-100F for 2 -
  4 weeks
• Buds removed and budded onto clean rootstock
• Or culture shoot apex in T.C.
• Grow from seeds! Viruses seldom enter a seed!

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Room for thermotherapy