Sexual propagation = production of new plants using seeds (or spores for ferns)

1. Sexual Propagation • Sexualpropagation = production of new plants using seeds (or spores for ferns) • Why propagate with seeds? • Easier, less expensive for some plants • Easier to ship and store • Some plants extremely difficult to propagate asexually • Invigorate declining performance of a plant line propagated asexually

2. Sexual Propagation • Seed storage • How should I care for the seeds I purchase? • Most seeds should be stored in dry, cool conditions • In general, 10% decrease in moisture doubles life of seeds • In general, 10% drop in temperature doubles life of seeds • Some seeds must be stored in moist, refrigerated conditions until planting in Spring (e.g. many native wildflowers in this area)

3. Sexual Propagation • Seed viability • How should I care for the seeds I purchase? • If seeds stored more than a year or two, you may wish to check viability (measure of potential to germinate) • Seed viability easily evaluated with tetrazolium (TZ) test • dry seeds cut to expose the embryo • tetrazolium chloride (colorless dye) applied to the embryo • After 30 minutes, seeds examined for the appearance of a red color, indicating respiratory activity • % of seed with red color is % viability (rarely printed on seed packages)

4. Sexual Propagation • Seed germination • How should I care for the seeds I purchase? • If seeds stored more than a year or two, you may wish to measure germination rate directly • Seed germination easily evaluated with petri dish test • small sample (10-20) from a seed lot placed in conditions • often seeds placed on moist filter paper in petri dishes and placed in environmental chamber • % of the sample that germinates measure of seed germination (often shown on a seed label )

5. Sexual Propagation • Seed germination • How should I care for the seeds I purchase? • Germination = resumption of growth and development of a seed or spore • Basic steps necessary for germination: • Seed absorbs water (imbibition) and obtains Oxygen to resume metabolic activity • Environmental signal breaks dormancy • Hormone signal used to stimulate production of enzyme to break down food reserves • Food reserves in endosperm or cotyledon used for rapid growth of seedling; first in radicle (root) then in plumule (shoot)

6. Sexual Propagation • Germination and early growth of seedlings • How should I care for the seeds I purchase? • Smaller seeds have less stored food than larger seeds • Rule-of-thumb: cover seeds with soil at depth of 3x seed diameter

7. Sexual Propagation • Seed dormancy • How should I care for the seeds I purchase? • Often need pre-germination treatment to break dormancy • Germination inhibited by seeds own physiology or anatomy • Dormancy an adaptation for surviving stressful conditions • Primarydormancy = dormancy occurs automatically after seed matures (or is harvested) • Secondarydormancy = dormancy induced after environmental stress

8. Sexual Propagation • Seed dormancy • How should I care for the seeds I purchase? • Primary dormancy caused by: • Immature embryos in seeds -- require proper after-ripening treatments (often high temperatures) to stimulate embryo development (e.g. most palms) • Programmed winter dormancy -- require cold, moist treatment called stratification (e.g. most native wildflowers, apples) • Chemical inhibition by fruit tissue -- require seeds are cleaned (e.g. flowering dogwood) • Hard seed coverings prevent imbibition and respiration -- requires scarification

9. Sexual Propagation • Seed dormancy • How should I care for the seeds I purchase? • Types of scarification: • File seed coat • Soak in hot water or acid • Exposed to dry heat (fire-adapted seeds) • Light may also be important cue to break dormancy (e.g. lettuce and tomato seeds) • Lettuce is positively photoblastic • Tomato negatively photoblastic

10. Sexual Propagation • Preparing seedlings for planting • How should I care for the seeds I purchase? • Seedlings started indoors need to be hardened off before planting • Hardeningoff = acclimating the seedlings to new (usually outdoor) conditions • Gradually decrease water and fertilizer • Gradually decrease temperature • Hardening off often done in cold frames