GUAVA

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BREEDING METHODS IN CROSS POLLINATED CROPS
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• Concept of Population Improvement
• Improving self-pollinated species tend to focus
  on improving individual plants.
• The methods of improving cross-fertilized species
  tend to focus on improving a population of
  plants.
• A population is a large group of interbreeding
  individuals.
• In the process of changing gene frequencies, new
  genotypes (that did not exist in the initial
  population) will arise.

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TypesIntrapopulation improvementInterpopulat
ion improvement.
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• Intrapopulation improvement.
• Selection is practiced within a specific
  population for its improvement for specific
  purposes. Intrapopulation improvement is suitable
  for
• Improving populations where the end product will
  be a population.
• Developing elite pure lines for hybrid
  production.
• Developing mixed genotype cultivars (in
  selffertilized species).

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2. Interpopulation improvement.

• Methods of interpopulation improvement entail
  selection on the basis of the performance of a
  cross between two populations.
• This approach is suitable for use when the final
  product will be a hybrid cultivar.
  Interpopulation heterosis is exploited.

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• Types of recurrent selection
• Simple recurrent selection.
• This is similar to mass selection with 1 or 2
  years per cycle.
• The procedure does not involve the use of a
  tester.
• Selection is based on phenotypic scores.
• This procedure is also called phenotypic
  recurrent selection.
• Recurrent selection for general combining
  ability.
• This is a half-sib progeny test procedure in
  which a wide genetic-based cultivar is used as a
  tester.
• The testcross performance is evaluated in
  replicated trials preceding to selection.

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• Recurrent selection for specific combining
  ability.
• This scheme uses an inbred line (narrow genetic
  base) for a tester.
• The testcross performance is evaluated in
  replicated trails before selection.
• Reciprocal recurrent selection.
• This scheme is capable of exploiting both general
  and specific combining ability.
• It entails two heterozygous populations, each
  serving as a tester for the other.

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Family selection methods

• General steps Family selection Creation of a
  family structure. Evaluation of families and
  selection of superior ones by progeny
  testing.Recombination of selected families or
  plants within families to create a new base
  population for the next cycle of selection.

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Half-sib family selection methods

• Half-sib or half-sib family selection is
  so-called because only one parent in the cross is
  known.

Ear-to-row selection

• Applications
• Half-sib selection is widely used for breeding
  perennial forage grasses and legumes.
• A polycross mating system is used to generate the
  half-sib families from selected vegetatively
  maintained clones.
• The families are evaluated in replicated rows for
  23 years.
• Selecting traits of high heritability is
  effective.

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Half-sib selection with progeny test

• Applications
• Recurrent half-sib selection has been used to
  improve agronomic traits as well as seed
  composition traits in corn.
• It is suited for improving traits with high
  heritability, and in species that can produce
  sufficient seed per plant to grow a yield trial.
• Species with self-incompatibility (no
  self-fertilization) or some other constraint of
  sexual biology (e.g., male-sterile) are also
  suited to this method of breeding.

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• Advantages
• The procedure is rapid to conduct.
• Progeny testing increases the success of
  selection, especially if quantitative gene action
  occurs or heritability is low.

• Disadvantages
• The trait of interest should have high
  heritability for success.
• It is not readily applicable to species that
  cannot produce enough seed per plant to conduct a
  yield trial.
• Lack of pollen control reduces heritability by
  half.

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• Full-sib family selection
• Full sibs are generated from biparental crosses
  using parents from the base population.
• The families are evaluated in a replicated trial
  to identify and select superior full-sib
  families, which are then recombined to initiate
  the next cycle.

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• Development of synthetic cultivars
• an advanced generation of cross-fertilized
  (random mating in all combinations) seed mixture
  of parents that may be strains, clones, or
  hybrids.
• The parents are selected based on GCA.
• A synthetic population differs from a natural
  population by consisting of breeder-selected
  parental stocks.

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• Year 1
• The source nursery
• The source population consists of clones.
• The source nursery is established by planting
  several thousands (5,00010,000) of plants
  assembled from many sources to provide a broad
  genetic base of the clonal lines for selection.
• The germplasm in the nursery is screened and
  evaluated to identify superior individuals
  according to the breeding objectives.

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• Year 2
• Clonal lines
• The breeder first selects 100200 superior plants
  on a phenotypic basis to multiply clonally to
  produce clonal lines.
• A clonal line nursery is established, each line
  consisting of about 2025 plants derived from the
  same parental line.
• The breeder may impose various biotic and abiotic
  selective pressures (e.g., drought) to aid in
  identifying about the 2550 most desirable
  clones.

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• Year 3
• Polycross nursery
• The selected clonal lines are planted in a
  polycross nursery to generate seed for progeny
  testing.
• Ideally, the layout of the polycross in the field
  should allow each clone to be pollinated by a
  random sample of pollen from all the other
  entries.
• Seed from each clone is harvested separately.
• The polycross test is valid if the layout ensures
  random interpollination.

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• Year 4
• Polycross progeny test
• Seed is harvested from the replicated clones and
  bulked for planting progeny rows for performance
  evaluation.
• The progeny test evaluates yield and other
  traits, according to the breeding objective.
• The top performing 510 clones are selected for
  inclusion in the synthetic cultivar.

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• Year 5
• Syn-0 generation
• The selected clones are vegetatively propagated
  and randomly transplanted into an isolated field
  for cross-fertilization to produce syn-0 seed.
• Leguminous species may be isolated in an
  insect-proof cage and cross-fertilized by using
  insects.

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• Year 6
• Syn-1 generation
• The syn-0 seed is increased by planting in
  isolation.
• Equal amounts of seed are obtained from each
  parent and mixed to ensure random mating in the
  field.
• Bulk seed is harvested from seed increased in the
  syn-1 generation, which may be released as a
  commercial cultivar provided sufficient seed is
  produced.

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• Year 7
• Subsequent syn generations
• Frequently, the syn-1 seed is not sufficient to
  release to farmers.
• It is further increased to produce syn-3
  (foundation seed) and syn-4 (certified seed).
• It is important to maintain the original clones
  so that the synthetic can be reconstituted as
  needed.
• The steps described are only generalized and can
  be adapted and modified according to the species
  and the objectives of the breeder.

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Factors affecting the performance of synthetic
cultivars

1. Number of parental lines used.
2. Mean performance of the parental lines (in
   syn-0).
3. Mean syn-1.

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• Advantages
• The method is relatively easy to implement.
• Used to produce variability for hybrid breeding
  programs.
• Advanced genotypes of synthetics show little
  yield reduction from syn-1, making it possible
  for farmers to save and use seed from the current
  season to plant in the next season.
• Disadvantages
• Because inadequate seed is often produced in
  syn-1, the method fails to exploit to the maximum
  the effects of heterosis, as is the case in
  conventional F1 hybrid breeding.
• Natural selection changes the genotypic
  composition of synthetics, which may be
  undesirable.

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