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PLANT BREEDING SYSTEMS: 

PLANT BREEDING SYSTEMS Diversity and Evolution of Reproduction in Angiosperms

Plants vs. Animals: 

Plants vs. Animals

Plants vs. Animals: 

Plants vs. Animals Flowering plants are generally hermaphroditic.

Plants vs. Animals: 

Plants vs. Animals Flowering plants are generally hermaphroditic. Use intermediary agents.

Plants vs. Animals: 

Plants vs. Animals Flowering plants are generally hermaphroditic. Use intermediary agents. Can reproduce asexually & sexually.

Plants vs. Animals: 

Plants vs. Animals Flowering plants are generally hermaphroditic. Use intermediary agents. Can reproduce asexually & sexually. Less rigidly controlled development meristematic tissue everywhere.

Asexual Reproduction: 

Asexual Reproduction Reproduction of genetically identical individuals from a single parent plant. Via cloning or agamospermy No meiosis, no fertilization, and no recombination.

Advantages of Asexual Reproduction: 

Advantages of Asexual Reproduction Parent plants well-adapted to local environment will have offspring with a competitive advantage.

Advantages of Asexual Reproduction: 

Advantages of Asexual Reproduction Parent plants well-adapted to local environment will have offspring with a competitive advantage. Colonization with limited dispersal.

Modes of Vegetative Reproduction: 

Modes of Vegetative Reproduction

Modes of Vegetative Reproduction: 

Modes of Vegetative Reproduction Rhizomes underground shoots Tillers aboveground shoots Bulblets “little bulbs” Bulbils inflorescence veg buds Cuttings

Agamospermy/Apomixis: 

Agamospermy/Apomixis “Seeds w/o gametes” Production of seeds genetically identical to parents asexually, w/o fertilization ~40 families, 130 genera, 400 species Obligative or facultative May have evolved independently multiple times from sexual ancestors.

Modes of Agamospermy: 

Modes of Agamospermy Embryo sac develops w/o meiosis w/ unreduced 2n egg cell & develops into zygote.

Modes of Agamospermy: 

Modes of Agamospermy Embryo sac develops w/o meiosis w/ unreduced 2n egg cell & develops into zygote. Embryo sac aborts and a veg cell from surrounding sporophytic tissue (ovary wall) develops into zygote. Rubus, Taraxacum officinale

Sexual Reproduction: 

Sexual Reproduction Production of offspring through meiosis and fertilization of egg by sperm (post-pollination). Offspring genetically different from parents due to recombination. Plants can be both asexual and sexual, with a variety of forms.

Hermaphroditic Flowers: 

Hermaphroditic Flowers Self-compatible (SC) Capable of self-fertilization or cross-fertilization Self-incompatible (SI) Only capable of cross-fertilization Inability of hermaphroditic plant to produce zygotes w/ self pollen

Autogamy : 

Autogamy Self-fertilization Pollen transfer within or among flowers of same individual ~25% of plant taxa

Advantages of Autogamy: 

Advantages of Autogamy

Advantages of Autogamy: 

Advantages of Autogamy Insures seed set in absence of pollinators.

Advantages of Autogamy: 

Advantages of Autogamy Insures seed set in absence of pollinators. Overcomes sterility.

Advantages of Autogamy: 

Advantages of Autogamy Insures seed set in absence of pollinators. Overcomes sterility. Selectively advantageous by transmitting both sets of genes to offspring. Well-adapted genotypes preserved.

Advantages of Autogamy: 

Advantages of Autogamy Insures seed set in absence of pollinators. Overcomes sterility. Selectively advantageous by transmitting both sets of genes to offspring. Well-adapted genotypes preserved. Only single colonizing individual needed.

Disadvantages of Autogamy: 

Disadvantages of Autogamy

Disadvantages of Autogamy: 

Disadvantages of Autogamy Decreases genetic variability.

Disadvantages of Autogamy: 

Disadvantages of Autogamy Decreases genetic variability. Inability to adapt to changing conditions.

Disadvantages of Autogamy: 

Disadvantages of Autogamy Decreases genetic variability. Inability to adapt to changing conditions. Increases inbreeding depression. Reduces heterozygosity and increases homozygosity of deleterious alleles. More uniform populations.

Cleistogamy (CL): 

Cleistogamy (CL) Flowers never open and only capable of self-fertilization in bud. Inconspicuous, bud-like apetalous flowers that form directly into seed capsules. Has evolved independently multiple times throughout the angiosperms, including some basal lineages. 488 species, across 212 genera and 49 families. Violaceae, Fabaceae, Poaceae

Cleistogamy (CL): 

Cleistogamy (CL) Mixed mating systems -can produce both CL and CH on an individual. CL fls are a “back-up” in case pollinators scarce. CL occur after normal flowering period. CH fls early spring and CL fls rest of season. CL fls occur through mutations with loss of SI.

Self-incompatibility (SI): 

Self-incompatibility (SI) Involves a biochemical rxn in the stigma/style to reject self pollen and prevent pollen tube growth. Genetically controlled by S-locus opposite S alleles attract like S alleles repel

Sporophytic SI: 

Sporophytic SI Diploid genotype of sporophyte parent determines what matings will be successful. Interaction between pollen exine and stigma/style tissues. Pollen will not germinate on stigma of flower that contains either of 2 alleles in sporophyte parent that produced pollen.

Gametophytic SI: 

Gametophytic SI Haploid genotype of pollen grain (gametophyte) determines what matings will be successful. Interaction between pollen tube and stigma/style tissues. Pollen grain will grow in any pistil that does not contain the same allele. 50% of angiosperms

Advantages of Self-Incompatibility: 

Advantages of Self-Incompatibility

Advantages of Self-Incompatibility: 

Advantages of Self-Incompatibility Prevents selfing and expression of deleterious genes that are heterozygous in parents.

Advantages of Self-Incompatibility: 

Advantages of Self-Incompatibility Prevents selfing and expression of deleterious genes that are heterozygous in parents. Reduces inbreeding depression.

Advantages of Self-Incompatibility: 

Advantages of Self-Incompatibility Prevents selfing and expression of deleterious genes that are heterozygous in parents. Reduces inbreeding depression. Increases genetic exchange/diversity.

Advantages of Self-Incompatibility: 

Advantages of Self-Incompatibility Prevents selfing and expression of deleterious genes that are heterozygous in parents. Reduces inbreeding depression. Increases genetic exchange/diversity. Ability to adapt to changing conditions.

Disadvantages of Self-Incompatibility: 

Disadvantages of Self-Incompatibility

Disadvantages of Self-Incompatibility: 

Disadvantages of Self-Incompatibility Relies on effective cross-pollination, seed dispersal and establishment.

Selfers vs. Outcrossers: 

Selfers vs. Outcrossers SC Small flowers (few) Unscented flowers Nectaries & nectar guides absent Maturation of reproductive parts Anthers near stigma Style included All fruits mature Low pollen/ovule ratio SI or SC Large showy flowers (many) Scented flowers Nectaries & nectar guides present Differential maturation of reproductive parts Anthers far from stigma Stigma well-exserted Only some fruits mature High pollen/ovule ratio

Strategies to Prevent Self-fertilization: 

Strategies to Prevent Self-fertilization

Physical Separation of Reproductive Parts (Herkogamy): 

Physical Separation of Reproductive Parts (Herkogamy) Within flowers Among flowers

Heterostyly: 

Heterostyly Flowers in different individuals of the same species having 2 or 3 different style lengths With stamen lengths varying inversely Distyly Tristyly

Distyly: 

Distyly 2 floral morphs. “Thrum” flower long filaments w/ short styles “Pin” flower short filaments w/ long styles Only pollinations between different floral morphs are successful. E.g.: Primula

Tristyly: 

Tristyly 3 floral morphs Style long, stamens short and medium Style medium, stamens short and long Style short, stamens medium and long

Slide45: 

Physical Separation of Reproductive Parts Unisexual flowers Staminate and carpellate flowers Monoecy Dioecy

Slide46: 

Monoecy Common in wind-pollinated plants. Common in temperate regions. Self-pollination possible but less likely.

Slide47: 

Dioecy 4% of angiosperms Scattered throughout Common in tropical regions and oceanic islands Gen small fl size 100% outcrossing, but inefficient Often controlled by sex chromosomes Silene

Slide48: 

Polygamous Flowers Both bisexual and unisexual fls on the same plant. Androdioecy = bisexual and staminate individuals in a population. Andromonoecy = bisexual and staminate flowers on same individual. Euphorbia, Solanum Gynodioecy = bisexual and carpellate individuals in a population. Sidalcea hendersonii, Silene Gynomonoecy = bisexual and carpellate flowers on same individual. Silene, Solidago Polygamodioecy = some plants with bisexual and staminate flowers & some plants with bisexual and carpellate flowers in a population. Polygamomonoecy = bisexual, staminate, and carpellate flowers on same individual.

Evolution of Dioecy: 

Evolution of Dioecy From hermaphroditism Vestigial sex organs Few families entirely dioecious From monoecy From SC W/in groups that have lost original GSI system From distyly Unequal pollen flow & gender function Change in pollinator frequency Non-functional anthers at low level in female flowers Non-functional pistil in male flowers

Temporal Separation of Reproductive Parts (Dichogamy): 

Temporal Separation of Reproductive Parts (Dichogamy)

Temporal Separation of Reproductive Parts (Dichogamy): 

Temporal Separation of Reproductive Parts (Dichogamy) Protandry Anthers release pollen before stigma receptive Common in insect-pollinated plants Geranium maculatum 1st day flower 2nd day flower

Temporal Separation of Reproductive Parts (Dichogamy): 

Temporal Separation of Reproductive Parts (Dichogamy) Protogyny Stigma receptive before pollen release Less common than protandry Magnolia grandiflora 1st day flower 2nd day flower

Geitonogamy: 

Geitonogamy Self pollination between different flowers on same plant.

Evolution of Breeding Systems: 

Evolution of Breeding Systems Evolutionary trends go both ways and in a variety of ways.

Evolution of Breeding Systems: 

Evolution of Breeding Systems Evolutionary trends go both ways and in a variety of ways. Ancestral angiosperms were SC, hermaphroditic.

Evolution of Breeding Systems: 

Evolution of Breeding Systems Evolutionary trends go both ways and in a variety of ways. Ancestral angiosperms were SC, hermaphroditic. SI has evolved many times. SC has evolved from SI plants as well.

Evolution of Breeding Systems: 

Evolution of Breeding Systems Evolutionary trends go both ways and in a variety of ways. Ancestral angiosperms were SC, hermaphroditic. SI has evolved many times. SC has evolved from SI plants as well. Physical and temporal separation have evolved many times.

Evolution of Breeding Systems: 

Evolution of Breeding Systems Evolutionary trends go both ways and in a variety of ways. Ancestral angiosperms were SC, hermaphroditic. SI has evolved many times. SC has evolved from SI plants as well. Physical and temporal separation have evolved many times. Dioecy has evolved many times.

Evolution of Breeding Systems: 

Evolution of Breeding Systems Evolutionary trends go both ways and in a variety of ways. Ancestral angiosperms were SC, hermaphroditic. SI has evolved many times. SC has evolved from SI plants as well. Physical and temporal separation have evolved many times. Dioecy has evolved many times. Breeding systems not fixed, but labile.