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