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Vegetative and Vegetative and Reproductive Reproductive
Growth & Growth & DevelopmentDevelopment
Plant Science-200Chapter 14
Germination involves Germination involves six stepssix steps Water imbibition Enzyme activation Hydrolysis & catabolism of storage
compounds Initiation of embryo growth Anabolism & formation of new cell
structures Emergence of seedling
Seed GerminationSeed Germination
WaterHeatOxygenLight
Seed Dormant Seed Dormant EmbryosEmbryosThick seed coatThin seed coatInsufficient developmentInhibitors
Seed Coat DormancySeed 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 Breaking seed dormancydormancy 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 TestingViability 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 TestGermination Test
Testing the % of seed that will germinate. Why is this important?
Roots and ShootsRoots and Shoots
The root and shoot systems grow in a balanced pattern
There are different methods of measuring growth
Definitions of Definitions of MeasurementMeasurement
Can be measured by:
Fresh weightVolumeLengthHeightSurface AreaAn increase in
size by cell division and enlargement
Types of Shoot growthTypes of Shoot growth
Determinate-flower bud develop at terminal buds halting growth
Indeterminate-No flower bud develops
Shoot growth PatternsShoot 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.
Perennial shoot Perennial shoot patternspatterns A Single flush followed by resting terminal
bud formation (fruit trees)
Recurrent flushes with terminal bud formation after flushes (citrus)
A flush followed by tip abortion after season (locust)
A sustained growth flush (sweet gum)
Reproductive growthReproductive growth
Fruit and seed production involves: Flower induction and initiation Flower differentiation and development Pollination Fertilization Fruit set and seed formation Growth and maturation of fruit and seed Fruit senescence
PhotoperiodismPhotoperiodism
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)
Environmental FactorsEnvironmental FactorsLightTemperatureWaterGases
Soil ConditionsNutrientsPestsPlant growth regulators and
horomones
What is light?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 What is meant by light quality?quality?
amount of light of different colorsplants absorb red & blue, reflect
greensmoke filters blue, sun looks redglass & plastic filter light
What is meant by light What is meant by light quantity?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?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 How does temperature influence crop influence crop selection?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 What are the Cardinal Temperatures?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 What is the Frost Free Period?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 How does snow cover affect the temperature affect the temperature of the soil?of the soil?
snow cover insulates, keeps warm
How can we keep a How can we keep a crop from freezing? crop from freezing? (orchards etc.)(orchards etc.)
heaters, smudge pots, irrigation, fans
WaterWater
Corn plant may have up to 2 Liters of water
Needed for metabolic functions
TranspirationEvaporationEvapotranspiratio
n
Gases Gases
The Primary gases are oxygen and Carbon dioxide
Oxygen needed for root function
CO2 is needed for stomatal opening
Phases changesPhases 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 & Flower Induction & InitiationInitiation
Mature flowers can be induced
Provide right conditions
What brings it about?
Photoperiodism
Vernalization
Fruit SetFruit 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 Fruit Growth and DevelopmentDevelopment
Movement of nutrients and plant chemicals to fruit
Strawberries are a good exampleUse of gibberellic acid to grapesTwo types of growth curvesS-curve (oranges, almonds)Double S-curves (stone fruits, grapes)
SenescenceSenescence
TerminalAnnuals-entire
plantWoody
perennials-leavesResins and
Phenols resist decay
Leaf:Root/shoot ratio decreases
Decline in photosynthesis