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Seeds and Seed Propagation

Introduction

  • Major method by which plants reproduce in nature.

  • Seed selection is crucial for domestication (food, fiber, medicine).

  • Over $23 billion market for seeds globally (corn, wheat, canola, soybean).

Seed Biology Basics

  • Development: Seeds grow into plants.

  • Dormancy: Seeds may not germinate under favorable conditions.

  • Germination: The process by which seeds begin to grow.

Seed Production and Handling

  • Seeds must be harvested at physiological maturity.

  • Drying and extraction processes vary by crop to ensure seed viability.

Techniques of Seed Propagation

  • Advantages:

    • Genetic diversity: Seeds can produce varied genotypes.

    • Cost-effective propagation.

    • Convenient storage due to dormancy and long shelf life.

    • Less disease introduction compared to other methods.

  • Disadvantages:

    • Genetic uniformity may be lost; seeds differ from parent plants.

    • Lengthy time to maturity for certain species (e.g., apple trees, potatoes).

Sources of Seeds

  • Self-pollination: Fertilizes same or similar plants, leading to fixed homozygosity.

  • Cross-pollination: Increases genetic variation; occurs with mechanisms to prevent self-pollination.

  • Apomixis: Seeds produced asexually, genetically identical to the mother plant.

Seed Structure

  • Composed of:

    • Seed coat (protective covering)

    • Storage tissue (endosperm, cotyledons)

    • Embryo (developing plant).

  • Additional parts include radicle (root) and plumule (shoot).

Stages of Seed Development

  1. Histodifferentiation: Embryo and endosperm differentiation.

  2. Cell expansion: Rapid growth due to storage accumulation.

  3. Maturation drying: Physiological maturity reaches high germination potential.

Dormancy and Germination

  • Dormancy: Prevents germination despite suitable environmental conditions, allowing for seed banks and seasonal synchronization.

  • Breaking Dormancy: Techniques include scarification, leaching, and stratification to stimulate germination.

Plant Hormones and Seed Development

  • Auxin: Signals fruit development.

  • Gibberellic Acid (GA): Induces germination and mobilizes resources for growth.

  • Abscisic Acid (ABA): Inhibits germination, maintaining dormancy.

Germination Process

  • Three phases:

    1. Water uptake (imbibition): Seeds absorb water.

    2. Lag phase: Mitochondria mature and proteins are synthesized.

    3. Radicle emergence: Growing root breaks through soil.

Seedling Emergence Patterns

  • Epigeous: Cotyledons emerge above soil (e.g., tomato).

  • Hypogeous: Cotyledons remain below soil (e.g., corn).

Seed Sources and Production

  • Commercial seed companies, seed exchanges, and collections from botanic gardens.

  • Production typically occurs in favorable climatic conditions to reduce disease.

Seed Certification**

  • Regulations to maintain genetic quality; includes categories like breeder's seed, foundation seed, registered seed, and certified seed.

Reading Seed Analysis Tags

  • Must include information such as germination percentage, pure seed weight, and lot number for traceability.