1. Variants in the Reproductive Process

2. Apomixis Substitute for sexual reproduction
Development of an embryo w/o sex
Identified in over 300 species across 37 families.
Not rare but relatively uncommon

3. Reproductive Behavior
Obligate Apomict: a plant which reproduces only by asexual reproduction.
Facultative Apomict: a plant which has the potential to reproduce either sexually or asexually. Both process may occur simultaneously or one may be predominant.
Within a genus or species, all reproduction strategies may be possible

4. Apomixis Must bypass two different processes:
Meiosis: no reduction of chromosome #
Fertilization: development of embryo w/o fusion of sperm and egg

5. Stimulus for Embryo Development
Autonomous: requires no further stimulation - embryo and endosperm may be developed before flowers open
Pseudogamy (False-fertilization): development of 2n gametophyte requires pollination and/or pollen tube growth. Sometimes a sperm nucleus fuses with polar nuclei, but never with egg

6. Genetics of Apomicts
Apomixis is genetically controlled in most cases studied
Control is complex (multigenic) and recessive to sexual reproduction
Polyploidy may affect apomictic reproduction
Hybridization tends to increase apomixis

7. Use of Apomixis in Breeding
Production of exact replicas of diploid
Fix hybrid vigor
Fix heterozygous status

8. Breeding and Pollination Systems

9. Plant Breeding Systems
General Issues to consider:
A flower is an adapted leaf specialized for sex.
Its function is to bring the gametes together thus
forming zygotes with new genetic combinations
A species’ survival is dependent on the production of offspring adapted to a particular environment. Plants have evolved a variety of adaptations that either encourage outbreeding (cross-pollination) or inbreeding (self-pollination or selfing).
Each breeding system has genetic ramifications

10. Basic Terms:
Outbreeding: Sexual reproduction between individuals (cross-pollination). (It involves two individual plants)
Inbreeding: Sexual reproduction within an individual
(self-pollination). (It involves one individual plant)
Sexual Reproduction: Meiosis and fertilization.
The sexual process is a mechanism to bring
about gene recombination. Recombination is the chief
source of hereditary variation and provides the raw
materials for species to adapt to changing
environmental conditions.

11. Outbreeder or Inbreeder??
Often one can tell just by looking at a flower whether it
cross-pollinates or self-pollinates
Trait
Incompatibility
Flower #
Flower size
Flower color
Nectories
Scent
Nector guides
Anther position
Pollen #
Style position
Stigma
OUTBREEDER INBREEDER
self-incompatible self-compatible
many flowers few flowers
large flowers small flowers
bright colors mono-colored
nectaries present nectaries absent
scented flowers unscented flowers
nectar guides present nectar guides absent
anthers far from stigma anthers close to stigma
many pollen grains fewer pollen grains
style exserted from flower style included in flower
stigmatic area well-defined stigmatic area poorly-defined

12. Outbreeding (Cross-pollination)
Advantages:
Increases genetic variability
Strong evolutionary potential
Adaptation to changing conditions
Successful long-term
Disadvantages:
Can destroy well-adapted genotypes
Relies on effective cross-pollination, seed
dispersal and establishment

13. Inbreeding (Self-pollination)
Advantages:
Preserves well-adapted genotypes
Insures seed set in the absence of pollinators
Single colonizing individual possible
Disadvantages:
Decreases (or maintains) genetic variability
Evolutionary dead-end
Cannot adapt to changing environmental conditions
Successful short-term