Vegetative and Reproductive Growth & Development Plant Science-200 Chapter 14

Germination involves six steps  Water imbibition  Enzyme activation  Hydrolysis & catabolism of storage compounds  Initiation of embryo growth  Anabolism & formation of new cell structures  Emergence of seedling

Seed Germination  Water  Heat  Oxygen  Light

Seed Dormant Embryos  Thick seed coat  Thin seed coat  Insufficient development  Inhibitors

Seed Coat Dormancy  Seed Coats or other tissues covering the embryo may be impermeable to water & gases, particularly oxygen. Thus we must use various artificial methods of softening seed coats.

Breaking seed dormancy  1. Scarification: The surface of the seed is mechanically scratched or ruptured.  2. Heat Treatment: Exposure to heat for a short period of time.  3. Acid Scarification: Soaking seeds in sulfuric acid.

Viability Testing  1- Cut Test: Cut the seed in half to see whether there is an embryo inside.  2- Float Test: Float the seed in water. Most often the floaters are empty seeds.  3- X-ray: Essentially the same as a cut test. You are looking inside the seed for an embryo, but don’t kill it.

Germination Test  Testing the % of seed that will germinate. Why is this important?

Roots and Shoots  The root and shoot systems grow in a balanced pattern  There are different methods of measuring growth

Definitions of Measurement  Can be measured by:  Fresh weight  Volume  Length  Height  Surface Area  An increase in size by cell division and enlargement

Types of Shoot growth  Determinate- flower bud develop at terminal buds halting growth  Indeterminate- No flower bud develops

Shoot growth Patterns  Annuals- Shoot growth commences after seed germination ceases sometime after flowering  Biennials-requires two growing seasons. Needs chilling to trigger stem elongation.  Perennials- Shoots and roots remain alive indefinitely.

Factors Affecting Plant growth & Development  Soil Conditions  Water use & requirements  Nutrients  Temperature  Light  Pests and Disease  Plant growth regulators & Horomones

Photoperiodism  Some plants needs a certain number of hours of day length to flower  Short day plants (i.e. poinsettias, strawberries, mums) need long nights uninterrupted to flower  Long Day plants (i.e. spinach sugar beets) need short nights  Day neutral (i.e. tomatoes)

What is light?  energy that travels in wavelengths  short wavelengths = high energy (blue)  long wavelengths = low energy (red)  ultraviolet = invisible

What is meant by light quality?  amount of light of different colors  plants absorb red & blue, reflect green  smoke filters blue, sun looks red  glass & plastic filter light

What is meant by light quantity?  amount of light energy received  measured in foot candles – summer day = 10,000 – living room = 20  crops need ,000  if not enough light, grow tall (leggy, weak stems)  weed control reduces competition for light  planting rate & row spacing  some plants need shade (tobacco), burlap, lathes, screens

What is light duration?  length of day  Long Day Plants more than13 hours  Short Day Plants less than 12 hours  Day Neutral Plants = no response

How does temperature influence crop selection?  Warm Season Crops - soil temp higher than 70 degrees (corn)  Cool Season Crops - soil temp lower than 70 degrees (wheat)

What are the Cardinal Temperatures?  minimum, maximum, optimal temperatures for a crop  wheat min=40 max=90 (when flowering)  crops generally don't grow in areas where average 24 hour temperature 130

What is the Frost Free Period?  the time from the last killing frost until the first killing frost of summer  at least 90 days  plant spring wheat when average soil temperature is 37 degrees

How does snow cover affect the temperature of the soil?  snow cover insulates, keeps warm

How can we keep a crop from freezing? (orchards etc.)  heaters, smudge pots, irrigation, fans

Water  Corn plant may have up to 2 Liters of water  Needed for metabolic functions  Transpiration  Evaporation  Evapotranspiration

Gases  The Primary gases are oxygen and Carbon dioxide  Oxygen needed for root function  CO 2 is needed for stomatal opening

Phases changes  Juvenile stage is different from mature stage due to inability to flower  Epigenetic changes are cause of change  Breeder want mature stock  Propagators want juvenile stock

Flower Induction & Initiation  Mature flowers can be induced  Provide right conditions  What brings it about?  Photoperiodism  Vernalization

Fruit Set  Certain hormones involved (auxin Gibberellin)  Optimal fruit set  Light fruit set is unprofitable  Heavy leads to small fruit poor quality  Thinning by chemical, hand or mechanical means

Fruit Growth and Development  Movement of nutrients and plant chemicals to fruit

Senescence  Terminal  Annuals-entire plant  Woody perennials- leaves  Resins and Phenols resist decay  Leaf:Root/shoot ratio decreases  Decline in photosynthesis