Plant Breeding Techniques Overview
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Plant Breeding Techniques Overview

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Questions and Answers

What is one major disadvantage of anther culture?

  • Enhanced linkage of traits
  • Increased genetic recombination
  • Higher variability in crops
  • Limited genetic recombination (correct)

    • At which stage of anther development is the most critical for successful culture?

  • Tetrad stage
  • Mature pollen stage
  • Microspore stage
  • Intermediate stage after 1st pollen anthesis (correct)

    • Which of the following factors is essential in producing anther culture?

  • High variability in plant responses
  • Avoidance of embryoid development
  • Selection of unrelated genotypes
  • Proper culture medium (correct)

    • What is stimulated by the presence of indeterminate gametophytes in the context of haploid production?

    <p>Development of male gametes</p> Signup and view all the answers

    Which method is typically used to alter one or two traits without affecting others in plant breeding?

    <p>Backcross methods</p> Signup and view all the answers

    What is the purpose of rapid generation advancement in plant breeding?

    <p>To quickly produce spaced type materials</p> Signup and view all the answers

    In the single seed descent method, how does the number of seeds planted vary each season?

    <p>It is determined by the number of genes controlling a trait</p> Signup and view all the answers

    What is the expected genotype frequency in the F2 generation for a single locus trait with dominance Aa?

    <p>1/4 AA, 1/2 Aa, 1/4 aa</p> Signup and view all the answers

    How many F2 plants are typically required when the parents are less related?

    <p>2000 plants are generally needed</p> Signup and view all the answers

    Which of the following describes the process of producing double haploids?

    <p>Using colchicine to double haploid chromosome complements</p> Signup and view all the answers

    What kinds of possible phenotypes are produced in the F2 generation when two genes are involved under complete dominance?

    <p>4 possible phenotypes with 9 genotypes</p> Signup and view all the answers

    What is one of the key steps involved in producing haploid plants using genetic markers?

    <p>Selecting for a dominant marker in the female parent</p> Signup and view all the answers

    How many possible genotypes are present in the F2 generation with three gene pairs under complete dominance?

    <p>27 genotypes</p> Signup and view all the answers

    What is the main characteristic of multilines?

    <p>They include a mixture of genetically different lines.</p> Signup and view all the answers

    What is one advantage of using multilines?

    <p>They can outperform the individual components' average yield.</p> Signup and view all the answers

    Which of the following is NOT a factor to consider in producing multilines?

    <p>Color of the seeds from each component</p> Signup and view all the answers

    Which type of intergenotypic competition occurs when actual performance is greater than expected?

    <p>Overcompensation</p> Signup and view all the answers

    What is a characteristic of the components in a multiline mixture?

    <p>They can include closely related or distinctly different lines.</p> Signup and view all the answers

    What is a disadvantage of multilines?

    <p>They require a long time to develop.</p> Signup and view all the answers

    How is the performance of a multiline variety predicted?

    <p>Multiplying the proportions of each component by their pure stand performance.</p> Signup and view all the answers

    What is an example of a multilines mixture?

    <p>A mixture of all green seed coat varieties of mungbean.</p> Signup and view all the answers

    What is the main feature of male sterility in plants?

    <p>The male gametes are nonfunctional.</p> Signup and view all the answers

    In which type of pollination control are male and female flowers found on different plants?

    <p>Diocy</p> Signup and view all the answers

    Which cross is incompatible in the heteromorphic system?

    <p>Thrum x thrum</p> Signup and view all the answers

    What characterizes the homomorphic pollination system?

    <p>Gametes' compatibility depends on the genotype of the gametophyte</p> Signup and view all the answers

    What type of system is the sporophytic system classified as?

    <p>Diplo-diplo system</p> Signup and view all the answers

    When pollen tubes grow slowly in styles with the same S allele, which system does this describe?

    <p>Gametophytic system</p> Signup and view all the answers

    What happens in a half compatible mating in the gametophytic system?

    <p>One parent has different S alleles.</p> Signup and view all the answers

    Which of the following is NOT an example of self-compatibility?

    <p>Orchids</p> Signup and view all the answers

    What is the outcome of crossing a male sterile plant (msms) with a fertile plant (MsMs)?

    <p>50% will be male fertile, and 50% will be male sterile.</p> Signup and view all the answers

    Which type of male sterility is determined by cytoplasm?

    <p>Cytoplasmic male sterility</p> Signup and view all the answers

    What defines apomixis in plant reproduction?

    <p>Seed formation without fertilization.</p> Signup and view all the answers

    Which system uses hybrid vigor to enhance rice yield?

    <p>Hybrid varieties</p> Signup and view all the answers

    What must farmers do when planting hybrid varieties?

    <p>Obtain new hybrid seed each planting from an accredited source.</p> Signup and view all the answers

    In which region is the hybrid variety PSBRc26H-Magat released?

    <p>Philippines</p> Signup and view all the answers

    Which chemical is used as a hybridizing agent to render pollen inviable?

    <p>Maleic hydrazide</p> Signup and view all the answers

    What is the primary benefit of using hybrid varieties over modern inbred rice varieties?

    <p>Increased yield potential.</p> Signup and view all the answers

    Study Notes

    Rapid Generation Advance

    • Used to advance generations of plants for selection, especially for traits controlled by multiple genes.
    • Multiple planting methods can be combined.

    Single Seed Descent

    • Number of seeds planted per season is not fixed.
    • Multiple seed descent involves planting a constant number of seeds (e.g., 3 seeds per plant) each season.

    Stabilization Phase

    • Achieved through continuous selfing, leading to increased homozygosity in the population.
    • Determining the number of F2 plants to grow depends on the number of genes controlling the trait.
    • Single locus trait:
      • F1 generation: Aa (heterozygous)
      • F2 generation: 1/4 AA : 1/2 Aa : 1/4 aa (genotypic ratio)
    • Calculating desirable genotype frequency in F2:
      • (3/4 + 1/4)^2 = (3/4)^2 + 2[(3/4) * (1/4)] + (1/4)^2 = 9/16 + 6/16 + 1/16 = 16/16 = 1 (whole population)
      • Desirable (b) = 7/16
    • For traits controlled by multiple genes:
      • Number of possible genotypes in F2 = 3^n (where n = number of gene pairs)
      • Number of possible phenotypes in F2 = 2^n (where n = number of gene pairs)
    • Number of F2 plants needed depends on the genetic diversity of the population, typically around 2000 plants for distantly related parents.
    • It can take 10-15 seasons to release a new variety, with purification requiring additional seasons.

    Double Haploid Techniques

    • Offer a faster approach to achieving homozygosity.
    • Involves two steps:
      • Producing haploid gametes or plants from a heterozygous source.
      • Doubling the chromosome complement of haploid plants, typically using colchicine.

    Methods for Obtaining Haploids

    • Genetic Markers:
      • Example: Corn with purple plant color and purple aleurone.
      • Female parent: recessive purple marker.
      • Male parent: dominant purple marker.
      • Harvest purple seeds, grow, and select for green plants.
      • Green plants are selfed and haploid with purple endosperm.
    • Naturally Occurring Paternal Haploid:
      • Search for green F1 plants with purple endosperm.
      • Frequency is very low.
    • Indeterminate Gametophytes:
      • Stimulates male gamete development.
      • Leads to a higher frequency of green F1 plants with purple endosperm.
    • Interspecific Crosses:
      • Example: Barley
      • Cross between Hordeum vulgare and Hordeum bulbosum.
      • Chromosomes of H. bulbosum are eliminated, leaving only chromosomes of H. vulgare.

    Anther Culture

    • Involves two processes:
      • Development of embryoids or calli from pollen cells.
      • Differentiation of embryoids into plants (regeneration).

    Factors Affecting Anther Culture

    • Source Plants:
      • Genotype (e.g., F1 = AaBbCcDdFf).
      • Disadvantages include limited genetic recombination and linkage breaking.
    • Stages of Anther Development:
      • Tetrad stage to intermediate stage after the first pollen anthesis is most critical.
    • Culture Media:
      • Proper culture medium is crucial for successful development.
      • Haploids are often short, uniform, and sterile.

    Multiple Crosses for Base Population

    • Large populations are needed to select desirable individuals.
    • Selecting closely related plants reduces recombination.
    • Aims for the formation of a broad-based population.

    Improvement of Existing Pure Lines

    • Backcross method: Changing one or two traits without altering others.
      • Requires two parents: adapted/established variety and a donor parent with desired traits.
    • Multilines:
      • A mixture of genetically different lines with the same desirable traits.
      • Consist of isoline lines (genetically identical except for the targeted trait)
    • Blends:
      • Lines with different traits.

    Commercially Accepted Multilines

    • Phenotypically the same lines but genetically different.
    • Example: All green seed coat varieties of mungbean.
    • Provide a stable alternative to crop rotation.

    Multilines Yield

    • Multilines often exceed the average yield of their component lines.
      • Observations:
        • 3.2% increase if components are unselected.
        • 7.45% increase if components are selected.

    Advantages of Multilines

    • Minimize genotype and environmental interaction effects.
    • More stable.
    • Resistant to diseases.
    • Improved yield performance.

    Forming Multilines

    • Development of isolines (genetically similar except for the targeted trait).
    • Using closely related lines (lines with a common parent).
    • Using distinctly different lines (each line complements the others).

    Predicting Multiline Performance

    • Performance of multiline = ∑ [Performance of component i in pure stand] * [Frequency of component i in mixture]
    • Example:
      • Var A: 100 units in pure stand, 25% proportion in mixture.
      • Var B: 110 units in pure stand, 75% proportion in mixture.
      • Performance of multiline = (100 * 0.25) + (110 * 0.75) = 107.5 units.

    Factors Affecting Multiline Production

    • Number of components and their relative frequency in the mixture.
    • Performance of the component lines in pure stand.

    Intergenotypic Competition

    • Deviation in multiline performance can occur due to competition among genotypes.
    • Types:
      • Undercompensation: Actual performance is lower than expected.
      • Complementary compensation: No competition, actual performance equals expected performance.
      • Overcompensation: Actual performance is higher than expected.

    Advantages of Multilines

    • Increased pest resistance.
    • Greater standability and longer lifespan.

    Disadvantages of Multilines

    • Long time required to develop.
    • Reconstruction of the mixture is needed to prevent varietal shift.
    • Seed certification challenges.

    Production of F1 Hybrids

    • No need to produce inbred lines in advance.
    • Test for combining ability (potential for different lines to produce high-yielding hybrids).
    • Requires emasculation (removal of male reproductive parts) or sterile lines.

    Composite Crosses

    • Produce and mix different lines, allowing for natural selection.
    • Genetically more diverse.
    • Subject to natural selection.

    Systems of Pollination Control in Plants

    • Mechanisms:
      • Dioecy: Male and female flowers are on separate plants (e.g., asparagus, rambutan, papaya).
      • Self-compatibility: Gametes are functional and can self-pollinate.
      • Heteromorphic: Difference in flower morphology, with two types:
        • Thrum: Short style, high anthers.
        • Pin: Long style, short anthers. o Thrum x Pin = Compatible. o Pin x Pin = Incompatible. o Thrum x Thrum = Incompatible.
      • Homomorphic: No difference in flower morphology.
        • Gametophytic System: Incompatibility depends on the genotype of the pollen (gametophyte).
          • Known as haplo-diplo system.
          • Controlled by a single locus with multiple alleles.
          • Pollen tube growth is slow if the style has the same S allele as the pollen.
          • Alleles act individually (no interactions or dominance).
        • Sporophytic System: Incompatibility is imparted to pollen by the plant (sporophyte) upon which the pollen is borne.
          • Known as diplo-diplo system.
          • Alleles may show individual action, dominance, or competitive effects.
      • Male Sterility: Gametes are nonfunctional.
        • Genetically Controlled: Due to a single gene or chromosomal aberration (e.g., sorghum, cotton, lima bean).
          • MsMs and Msms = Fertile; msms = Sterile.
        • Cytoplasmically Controlled: Sterility is determined by the cytoplasm (e.g., corn).
        • Cyto-genetically Controlled: Controlled by both cytoplasm and genes (e.g., sorghum, onion, rice).
        • Chemically Controlled: Pollen viability is affected using chemical hybridizing agents (e.g., maleic hydrazide, ethrel, FW 450).
      • Apomixis: Seed formation without fertilization.

    Hybrid Varieties

    • Exploit hybrid vigor to increase yield potential, especially in modern rice varieties.
    • F1 seed is obtained from a cross between two inbred parents.
    • Farmers must obtain new hybrid seed for each planting from a certified source.
    • Ex:
      • China: Zhen Shan 97 A/Min-Hui 63 and V20 A/Ce 64.
      • India: DRRH-1 and PA6201.
      • Philippines: PSBRc26H–Magat and PSBRc72H-Mestizo.

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