Exam 2 Study Guide - Plant Propagation & Climate

Administrative & Exam Details

• Exam Logistics:

  • The exam is closed-note and conducted in class.

  • Exam Date: Wednesday, October 1st.

  • Allowed Materials: A single-sided, hand-written cheat sheet no larger than $8.5 \times 11\text{ inches}$.

• Main Lecture Topics Covered:

  • Unit 5: Growth Stimulants, Retardants, & Hormones

  • Unit 6: Seeds

  • Unit 7: Softwood and Semihardwood Cuttings

  • Unit 8: Hardwood Cuttings

  • Unit 9: Separation & Division

  • Units 10 & 11: Grafting & Budding

  • Unit 12: Layering

  • Climate & Precipitation Supplement Notes

Growth Stimulants, Retardants, & Hormones

• Core Definitions:

  • Plant Hormones (Phytohormones): Naturally occurring organic compounds produced internally by plants in low concentrations that regulate physiological processes, development, growth, and cellular differentiation.

  • Plant Growth Regulators (PGRs): Synthetic or naturally derived chemical compounds applied externally to plants to alter growth, development, or physiological activity.

• The Seven Primary Plant Hormone Groups:

  • Jasmonic Acid:

  • Primary role in plant defense response to pathogens and herbivore stress.

  • Signals Induced Systemic Resistance (ISR).

  • Retardant/Inhibitor function: Inhibits overall plant growth and seed germination.

  • Developmental functions: Promotes flower development, fruit ripening, leaf abscission, plant senescence, pigment formation, tendril coiling, and triggers tuber formation.

  • Serves as an essential internal signal in response to physical plant wounding.

  • Salicylic Acid:

  • Involved in regulating growth, photosynthesis, transpiration, and root ion uptake/transport.

  • Triggers Systemic Acquired Resistance (SAR) against localized pathogen attacks.

  • Retardant/Inhibitor function: Inhibits seed germination, blocks ethylene production, and suppresses wound responses.

  • Commercial applications: Promotes flower longevity; commercially synthesized as acetylsalicylic acid (aspirin).

  • Auxins:

  • First plant hormone discovered.

  • Promotes adventitious root formation on stem cuttings.

  • Regulates underground tuber and bulb development.

  • Prevents premature fruit drop, defoliation, and leaf/fruit abscission.

  • Maintains plant juvenility.

  • Produced primarily in the terminal/apical bud, driving apical dominance by suppressing the sprouting of lateral (axillary) buds lower on the stem.

  • Gibberellins:

  • Stimulates stem elongation and cell division.

  • Breaks dormancy in seeds, terminal buds, and underground tubers.

  • Increases flower, leaf, and fruit sizes.

  • Induces early flowering in plants.

  • Cytokinins:

  • Interacts with light to promote cell division (cytokinesis) and cell enlargement.

  • Known as the "youth hormone" because it slows aging, delays leaf abscission, and prevents chlorophyll degeneration (chlorosis).

  • Stimulates lateral bud growth and breaks apical dominance.

  • Ethylene:

  • Exists as a gas that accelerates fruit ripening and ages plant structures such as mature flowers.

  • Induces flowering in pineapples and bromeliad family members.

  • Retardant/Inhibitor function: Acts as a natural plant growth retardant.

  • Abscisic Acid (ABA):

  • Retardant/Inhibitor function: Potent growth retardant that induces leaf drop (abscission) and plant/seed dormancy.

  • Regulates stomatal closure during drought stress to prevent desiccation.

  • Slows stem elongation, resulting in sturdier, compact, and fuller plant growth.

• Plant Defense Mechanisms:

  • Induced Systemic Resistance (ISR):

  • Activated by non-pathogenic rhizobacteria or localized pest/pathogen attacks.

  • Mediated internally via jasmonic acid and ethylene signaling pathways.

  • Prepares the entire plant system to mount a broader defense response.

  • Systemic Acquired Resistance (SAR):

  • Activated by a localized pathogen attack on older foliage.

  • Results in system-wide resistance against that specific pathogen in younger leaves.

  • Mediated internally via salicylic acid signaling pathways.

• Plant Tropisms:

  • Tropism: Directional growth or movement of a plant in response to an external environmental stimulus.

  • Phototropism: Directional growth response to light direction and quality.

  • Geotropism (Gravitropism): Directional growth response to gravity (roots display positive geotropism; stems display negative geotropism).

  • Thigmotropism: Directional growth response to physical touch or mechanical contact (e.g., tendril coiling around support structures).

• Additional Growth Regulation Concepts:

  • Allelopathy: Chemical inhibition of one plant species by another through the release of biochemical substances (allelochemicals) into the surrounding root zone or environment.

  • Pinching Agents: Chemical sprays or manual pruning techniques that destroy or remove the apical bud to break apical dominance and encourage bushier, lateral shoot growth.

  • Apical Dominance: Phenomenon where auxin produced in the apical meristem inhibits the growth of axillary buds along the stem.

Seeds & Sexual Propagation

• Propagation Types:

  • Sexual Propagation: Production of offspring through the fusion of haploid male and female gametes to create a genetically unique diploid zygote within a seed.

  • Vegetative (Asexual) Propagation: Production of offspring using vegetative plant parts (stems, leaves, roots), producing genetically identical clones of the parent plant.

• Requirements for Sexual Propagation:

  • Production of viable functional pollen and egg cells.

  • Successful transfer of pollen (pollination).

  • Fertilization and embryonic development.

  • Mature seed structure with viable embryo, endosperm/cotyledons, and intact seed coat.

  • Suitable external conditions for germination (water, oxygen, temperature, and light).

• Stages of Plant Life Cycles:

  1. Germination: Activation of seed embryo metabolism and emergence of embryonic root and shoot structures.

  2. Juvenility: Period of rapid vegetative growth where the plant cannot be induced to flower or reproduce sexually.

  3. Maturity: Phase where vegetative growth slows and the plant becomes capable of flowering, fruiting, and seed production.

  4. Senescence: Terminal stage of the plant life cycle involving natural degradation, breakdown of tissues, and eventual cell death.

• Pollination & Fertilization Mechanics:

  • Pollination Definition: The physical transfer of pollen grains from the male anther to the receptive female stigma.

  • Fertilization: A haploid male sperm cell and a haploid female egg cell unite to form a diploid zygote, which matures into an embryonic plant inside a seed.

  • Fruit Formation: Following successful fertilization, the surrounding ovary matures into a fruit containing one or more developed seeds.

• Plant Life Cycle Strategies:

  • Annual: Completes its entire life cycle from germination to seed production and death within a single growing season.

  • Biennial: Requires two full growing seasons to complete its life cycle (vegetative growth and overwintering in year one; flowering, seed set, and death in year two).

  • Perennial: Lives for more than two years, flowering and setting seed repeatedly across multiple growing seasons.

  • Monocarp: Vegetatively grows for multiple years or decades, flowers and sets seed only once in its entire lifespan, and dies immediately afterward.

• Flowering Mechanisms:

  • Plants sense the optimal timing for flowering through photoperiodism (sensing duration of light vs. darkness using phytochrome pigments) and temperature thresholds (e.g., vernalization requirements).

• Anatomy of a Seed:   

  

  • Seed Coat (Testa): Outer protective covering shielding internal seed structures from physical damage and water loss.

  • Endosperm: Nutritive tissue storing starches, lipids, and proteins to sustain embryonic growth (prominent in monocotyledons like corn).

  • Embryo: The young undeveloped plant contained within the seed, consisting of:

  • Cotyledons: Seed leaves that store or absorb nutrients for the germinating seedling.

  • Radicle: Embryonic root stem.

  • Plumule/Epicotyl: Embryonic shoot tip.

• Seed Dormancy & Methods to Break It:

  • Dormancy Definition: A physiological condition preventing viable seeds from germinated even under favorable moisture, temperature, and oxygen conditions. Protects seedlings from emerging during unfavorable seasons.

  • Types of Seed Dormancy:

  • Physical (Exogenous) Dormancy: Hard, thick seed coat impermeable to water and gases. Broken by scarification (mechanical abrading, hot water soak, or chemical acid dip).

  • Physiological (Endogenous) Dormancy: Internal chemical growth inhibitors (e.g., high ABA concentration). Broken by stratification (chilling under moist, aerated conditions for a specified period).

  • Double Dormancy: Combination of both physical seed coat restriction and internal physiological dormancy. Broken by scarification followed by chilling stratification.

• Germination Sequence:

  • First structure to emerge from the seed: The radicle (embryonic root).

  • First structure to break the soil surface: The hypocotyl (in epigeal emergence, pulling cotyledons up) or epicotyl (in hypogeal emergence, keeping cotyledons below ground).

  • Cotyledons: Embryonic seed leaves providing stored energy to the seedling until true foliage establishes photosynthesis.

Softwood & Semihardwood Cuttings

• Comparison of Cuttings:

  • Softwood (Herbaceous) Cuttings: Taken from succulent, tender new growth of current spring shoots. Roots quickly but desiccates and wilts rapidly if humidity drops.

  • Semihardwood Cuttings: Taken from partially matured, firm stems of current season growth in mid-to-late summer. Stem tissue is partially woody with fully expanded leaves.

• Semihardwood Propagation Procedure:

  • Timing: Collect cuttings in mid-to-late summer during cool morning hours when tissue turgor pressure is high.

  • Harvesting: Cut $3 - 6\text{ inch}$ shoot tips just below a node.

  • Preparation: Strip lower leaves to expose nodes and reduce transpiration while leaving upper leaves intact.

  • Hormone Treatment: Dip cut base into root-promoting auxins (e.g., IBA or NAA).

  • Insertion: Insert into sterile, well-draining rooting substrate and maintain under high humidity.

• Minimizing Water Loss on Cuttings:

  • Keep foliage moist using intermittent mist systems or fogging setups.

  • Cover propagation trays with clear plastic humidity domes.

  • Reduce leaf surface area by trimming large leaves in half.

  • Provide partial shading to minimize transpirational heat stress.

• Micropropagation (Tissue Culture):

  • In vitro propagation technique growing tiny tissue explants under sterile conditions on nutrient agar media.

  • Why not recommended for home gardeners: Demands specialized equipment, sterile laboratory facilities, expensive chemical media, exact climate controls, and high technical expertise to avoid fungal and bacterial contamination.

Hardwood Cuttings

• Asexual vs. Sexual Propagation Comparison:

  • Asexual propagation creates genetically identical clones, preserves true-to-type cultivar traits, bypasses long juvenile phases, and propagates seedless plants.

• Woody Cutting Classifications & Features:

  • Hardwood Cuttings: Taken from fully dormant, mature, woody stems during late fall, winter, or early spring.

  • Types: Straight cuttings, heel cuttings (includes small piece of older wood), and mallet cuttings (includes entire cross-section of older stem).

  • Easiest & Least Expensive Method: Hardwood cutting propagation is the easiest and least expensive vegetative technique because dormant stems lack leaves (eliminating misting system needs), resist desiccation, store easily, and require minimal equipment.

• Hardwood Cutting Procedure:

  • Collect dormant, straight shoots with healthy buds during winter.

  • Make a flat cut right below a basal node and an angled cut above a terminal bud.

  • Apply rooting hormone (auxin) to the base.

  • Bundle cuttings and store in cool, moist media for callus development, or plant directly in field beds.

• The Callus Period:

  • Callus is an unorganized mass of parenchyma cells formed over wound sites.

  • Serves as a vital protective layer and precursor tissue from which adventitious root primordia differentiate.

• Environmental Requirements:

  • Cool atmospheric temperatures (to prevent premature shoot bud break) combined with warm basal soil temperatures (to encourage root initiation).

  • Moist, well-aerated soil substrate.

Separation & Division

• Terminology:

  • Separation: Propagation method using naturally detachable reproductive structures (e.g., bulbs, corms) produced by the parent plant.

  • Division: Propagation method where modified stem or root structures (e.g., rhizomes, tubers, tuberous roots) are physically cut or divided into pieces, each containing a vegetative bud or eye.

  • Bulb: Underground modified shoot consisting of a short stem base (basal plate) surrounded by fleshy, modified scale leaves storing nutrients.

  • Bulblet: Secondary bulb produced at the base of a mother bulb.

  • Offset Bulb: Fully grown bulblet detached from the primary bulb.

  • Corm: Solid, swollen vertical underground stem tissue surrounded by thin, dry papery leaves.

  • Cormel: Small secondary corm arising from the base of a mother corm.

• Anatomy & Structure Identification:   

  

  
  

  • Bulb Components: Flower Bud, Foliage Leaves, Bulb Scales, Lateral Bulblets, Basal Plate, Contractile Roots.

• Corm Components: Stalk, New Corm, Cormels, New Fleshy Roots, Old Corm, Old Contractile Fibrous Roots.

• Rhizome: Horizontal underground stem showing foliage shoots and root networks.

• Potato Tuber: Shows eyes/buds and designated cut lines. A piece without a bud will fail to grow; every division cut piece must retain at least one bud or eye.

• Tuberous Root: Fleshy storage root attached to central shoot crown.

  • Categorization of Plant Structures:

• Structures Separated: Bulbs (tulips, onions, lilies) and Corms (gladiolus, crocus).

• Structures Divided: Rhizomes (iris, ginger), Tubers (potato), Tuberous Roots (dahlia, sweet potato), and Herbaceous Perennial Crowns (hosta, daylily).

Grafting & Budding

• Terminology:

  • Scion: Upper shoot section with desirable foliage, flower, or fruit traits grafted onto rootstock.

  • Rootstock (Understock/Stock): Lower root-bearing portion providing subterranean root systems and anchoring.

  • Grafting: Art of joining stem sections from two plants so their vascular systems fuse and grow as a single plant.

  • Budding: Form of grafting where a single vegetative bud attached to a small piece of bark/wood is inserted onto rootstock.

• Reasons for Grafting and Budding:

  • Propagates cultivars that cannot be rooted from cuttings or raised true-to-type from seed.

  • Imparts rootstock benefits such as disease resistance, cold hardiness, soil adaptability, and growth dwarfing.

  • Enables top-working (changing fruit varieties on established trees).

  • Repairs structural stem trunk damage (bridge grafting).

  • Accelerates plant reproductive maturity.

• Importance of Vascular Cambium:

  • The cambium layer contains actively dividing meristematic cells.

  • Successful graft unions require direct physical contact between the vascular cambium of the scion and rootstock to enable cell bridge proliferation.

• Graft Union Healing Process:

  1. Alignment and close contact between scion and rootstock cambium tissues.

  2. Production of unorganized callus tissue by cambium layers of both components.

  3. Interlocking and formation of a continuous callus bridge across the graft interface.

  4. Differentiation of new vascular cambium within the callus bridge.

  5. Formation of continuous functional xylem (water transport) and phloem (nutrient transport) vessels.

• Grafting Techniques by Diameter Alignment:

  • Scion and Rootstock of Equal Diameter:

  • Whip-and-tongue graft

  • Splice graft

  • Rootstock Larger than Scion Diameter:

  • Cleft graft

  • Bark graft

  • Side graft

  • Notch / Veneer graft

  • Diameter Requirement Rationale: Rootstock diameter must be equal to or larger than scion diameter to structural support and adequate hydraulic vascular supply to upper tissues.

  • Repair Grafting Techniques: Bridge graft and Inarch grafting.

• Benefits of Budding over Grafting:

  • High material efficiency: Uses a single shoot bud per new plant.

  • Faster execution rates and stronger structural union.

  • Extremely common commercial methods include T-budding (shield budding) and chip budding.

Layering

• Layering Concept:

  • Vegetative propagation technique where root formation is induced on a stem while it remains fully attached to the parent plant.

  • Popular because parent plant continuously supplies water and carbohydrates, eliminating moisture stress during rooting.

• Vascular Disruption Mechanics:

  • Stem wounding, bending, or girdling disrupts phloem tissue (downward transport of auxins and carbohydrates) causing local hormone accumulation at the wound site to trigger adventitious rooting.

  • Xylem tissue remains intact, supplying continuous upward water and mineral flow.

• Types of Layering:

  • Simple Layering: Lower flexible stem bent to ground, wounded, and pegged under soil leaving stem tip exposed.

  • Air Layering: Stem bark girdled aerial stem wrapped in moist sphagnum moss and sealed with plastic wrap.

  • Trench Layering: Entire branch laid flat inside a shallow ground trench; emerging upright shoots buried progressively to induce roots.

  • Stool (Mound) Layering: Plant cut back to ground level in spring; soil mounded over emerging shoots to induce basal roots.

  • Compound (Serpentine) Layering: Single long stem woven into and out of soil at multiple intervals.

Climate & Precipitation

• Atmospheric & Spatial Definitions:

  • Weather: Current, short-term atmospheric conditions at a specific time and location.

  • Climate: Long-term pattern and statistical average of atmospheric conditions over multi-decade timeframes.

  • Macroclimate: Regional atmospheric conditions encompassing large areas ($24 - 50\text{ miles}$ or more).

  • Local Climate: Atmospheric conditions influenced by local terrain features over smaller localized areas (e.g., valleys, tree stands, fields, hillsides).

  • Microclimate: Environmental conditions surrounding a tiny area (e.g., inside vs. outside a leaf canopy, upper vs. lower leaf surfaces, south wall exposure).

• Climatic Zones & Location:

  • Tropical Zone: Equatorial region between Tropic of Cancer ($23.5^\circ\text{N}$) and Tropic of Capricorn ($23.5^\circ\text{S}$).

  • Temperate Zone: Mid-latitude regions located between $23.5^\circ$ and $66.5^\circ$ North and South latitudes.

  • Arctic (Polar) Zone: High-latitude polar regions located above $66.5^\circ$ North and South latitudes.

  • United States Location: Primarily situated within the Temperate Climatic Zone.

• Microclimate Examples:

  • Indoor: South-facing window ledge (high light/heat) vs. dark hallway; inside greenhouse vs. exterior shaded bench.

  • Outdoor: Warm microclimate along south-facing brick wall; cool frost pocket in low elevation ground depressions; shaded woodland floor under canopy.

• Seasonality & Planetary Drivers:

  • Cause of Seasons: The tilt of Earth's rotational axis ($23.5^\circ$) relative to its orbital plane around the Sun.

  • Summer Solstice: Day with maximum sunlight hours (approx. June 21 in Northern Hemisphere); Sun positioned directly over Tropic of Cancer.

  • Winter Solstice: Day with minimum sunlight hours (approx. December 21 in Northern Hemisphere); Sun positioned directly over Tropic of Capricorn.

  • Yearly Growth Flush: Rapid surge of primary stem elongation and new leaf expansion during spring.

• Seasonal Plant Transitions:

  • Spring: Sap movement resumes, buds break dormancy, vegetative growth flushes, early flowering occurs.

  • Summer: Active photosynthetic carbohydrate production, fruit set, leaf cuticle thickening, flower bud initiation for following year.

  • Fall: Growth cessation, carbohydrate allocation to storage, leaf senescence, leaf abscission, cold hardening.

  • Winter: Dormancy maintenance, chill hour accumulation, cellular cold acclimation.

• Elevation & Water Impacts:

  • Elevation Changes: Temperature decreases with increasing altitude (approximate drop of $3.5^\circ\text{F}$ to $6.5^\circ\text{F}$ per $1,000\text{ feet}$ of elevation gain).

  • Water Body Effects: Large water bodies moderate regional climates, creating milder winters, cooler summers, delayed spring growth, and extended fall growing seasons due to water's high specific heat capacity.

• The Five Climate Elements:

  1. Temperature

  2. Precipitation (Moisture/Humidity)

  3. Light (Solar radiation intensity and photoperiod)

  4. Wind

  5. Atmospheric Pressure & Air masses

• Cold Hardiness & Temperature Maps:

  • Cold Hardiness: Innate ability of a plant to withstand cold winter minimum temperatures without cellular freeze damage.

  • Frost-Tender: Plants injured or killed by freezing temperatures ($0^\circ\text{C} / 32^\circ\text{F}$).

  • Frost-Hardy: Plants capable of surviving freezing or sub-zero temperatures without injury.

  • USDA Plant Hardiness Zone Map: Map based on average annual extreme minimum winter temperatures divided into $10^\circ\text{F}$ zones (further split into $5^\circ\text{F}$ subzones 'a' and 'b').

  • AHS Heat Zone Map: Map based on the average annual number of days where temperatures exceed $86^\circ\text{F} (30^\circ\text{C})$, the physiological threshold where plant thermal stress and protein denaturation begin.

• Symptoms of Excessive Heat in Plants:

  • Leaf scorch and leaf margin desiccation.

  • Wilting despite presence of soil moisture.

  • Sunscald on bark and fruit surfaces.

  • Abscission of flower buds, open flowers, and young fruit.

  • Stunted growth caused by respiration rates exceeding photosynthetic production.

Here are additional key details from your notes to fill the remaining space on your cheat sheet: 1. Cuttings Comparison: Softwood cuttings are taken from succulent spring growth, root quickly, but wilt fast. Semihardwood cuttings are taken in mid-to-late summer from partially woody stems with expanded leaves. Hardwood cuttings are taken from dormant, mature woody stems during winter; they are the easiest and least expensive vegetative method because dormant stems lack leaves, eliminate misting needs, resist desiccation, and store easily. 2. The Callus Period: Callus is an unorganized mass of parenchyma cells formed over wound sites that serves as precursor tissue from which adventitious root primordia differentiate. 3. Hardwood Environmental Requirements: Requires cool atmospheric temperatures to prevent premature shoot bud break combined with warm soil temperatures to encourage root initiation. 4. Micropropagation: In vitro growth on nutrient agar; not recommended for home gardeners because it demands specialized equipment, sterile laboratory facilities, expensive media, and high technical expertise to avoid contamination. 5. Plant Tropisms & Terminology: Phototropism (light response), Geotropism/Gravitropism (gravity response: roots positive, stems negative), Thigmotropism (touch response). Allelopathy is chemical inhibition of one plant species by another. Pinching agents destroy/remove the apical bud to break apical dominance and encourage bushier growth. 6. Plant Life Cycle Stages: Germination -> Juvenility (rapid growth, cannot flower) -> Maturity (growth slows, capable of flowering) -> Senescence (natural degradation and cell death).

Key Exam & Plant Propagation Concepts

• Exam Details: Closed-note exam on Wednesday, October 1st. Allowed one single-sided hand-written cheat sheet ($8.5 \times 11\text{ inches}$).

• Plant Hormones & Defense:

  • Auxins: Apical dominance, rooting promotion, and prevention of leaf/fruit abscission.

  • Gibberellins: Stem elongation, breaking seed/bud/tuber dormancy, and increasing fruit/flower size.

  • Cytokinins: Promotes cell division and delays leaf senescence/chlorosis ("youth hormone").

  • Ethylene: Gaseous growth retardant, fruit ripening agent, and flower aging stimulant.

  • Abscisic Acid (ABA): Stress growth retardant, closes stomata during drought, and induces dormancy.

  • Jasmonic Acid: Wounding and defense signal mediating Induced Systemic Resistance (ISR).

  • Salicylic Acid: Growth and photosynthesis regulator mediating Systemic Acquired Resistance (SAR).

• Propagation Methods:

  • Sexual Propagation: Genetic variation via seed fertilization. Dormancy broken via scarification (physical seed coat) or stratification (physiological chilling). Radicle emerges first during germination.

  • Softwood & Semihardwood Cuttings: Taken from active spring/summer growth; requires humidity and misting to prevent desiccation. Micropropagation requires sterile lab environments.

  • Hardwood Cuttings: Taken from dormant winter wood; easiest and least expensive vegetative method. Requires cool air and warm soil for callus formation.

  • Separation & Division: Separation uses detachable natural structures (bulbs, corms). Division requires cutting tissue retaining buds/eyes (rhizomes, tubers, tuberous roots).

  • Grafting & Budding: Scion joined to rootstock requiring strict cambium alignment for callus bridge creation. Budding uses a single bud piece.

  • Layering: Induces adventitious roots on stems attached to parent plant by interrupting downward phloem transport while maintaining upward xylem water flow.

• Climate & Environmental Horticulture:

  • Seasons & Temperature: Axial tilt of $23.5^\circ$ drives seasons. Altitude decreases temperature by $3.5^\circ\text{F} - 6.5^\circ\text{F}$ per $1,000\text{ feet}$ gain.

  • Hardiness & Heat Maps: USDA Map categorizes zones based on average extreme minimum winter temperatures ($10^\circ\text{F}$ zones); AHS Heat Map categorizes zones by annual days exceeding $86^\circ\text{F} (30^\circ\text{C})$.