Transcript Chapter 14
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 IndeterminateNo 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 100-10,000 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 <50 or >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 CO2 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 perennialsleaves Resins and Phenols resist decay Leaf:Root/shoot ratio decreases Decline in photosynthesis