Chapter 15. Plant Growth Regulation

I. BIOLOGICAL CONTROL

    A. Graft Combination
        1.Restriction of Growth
            -Use of dwarfing root stock
            -Use of dwarfing interstock

Apple - dwarfing rootstocks
-East Malling (EM) series
-Malling Merton (MM) series

Pear - use of 'Angers' quince rootstock

        2. Stimulation of Growth
            -Pear-Apple hybrid grafted on pear or apple rootstocks
            -Juniperus virginiana grafted on J. chinensis

        3. For Flowering and Productivity
            -Sweet potato grafted on Morning glory
            -Certain rootstocks hasten flowering

B. Phloem Disruption
1. Bark inversion 2. Ringing 3. Scoring

C. Population Competition

        1. Interplant competition - between plants
            -plant size affected by planting density
            -total yield per unit area
        2. Intraplant competition - within a plant
            -Fruit thinning
            -Flower and fruit quality (disbudding)

D. Mechanical Stress

        1. Rubbing and touching reduces plant height
            Thigmomorphogenesis
        2. Shaking reduces plant height
            Seismomorphogenis

II. CHEMICAL CONTROL

    A. Rooting of Cuttings
        -Auxins promote adventitious roots
        -Indolebutyric acid (IBA)
            liquid - 50% ETOH
            powder - diluted by talc

    B. Growth Promotion
        -Auxins, cytokinins, Gibberellins
            NAA BA GA₃
        -Multiple branching, flower stem length (GA₃), fruit set
    C. Defoliation
        -Ethephon (Ethylene), Abscisic acid (ABA)
        -used in cotton harvesting
            Defoliant

    D. Flower Induction
        -'Florigen' an elusive chemical
        -Use of auxins and ethephon (ethylene)

-Flower induction in pineapple and bromeliads
NAA, 2, 4-D, Ethephon - Ethrel^®

    E. Flower Sex Conversions
        -Gibberellins (GA₃) promote maleness
        -Ethylene and auxins promote femaleness

Cucumber:

Muskmelon:

    F. Fruit Thinning
        -Auxin derivatives (peach, apple, pear)
        -Gibberellins (grape) - grapes

    G. Fruit Ripening
        -Ethylene gas
        -Ripening of banana, tomatoes

    H. Parthenocarpy
        -Development of fruit without pollination
        -Auxins, gibberellins
            greenhouse cucumbers - seedless cultivars (Holland)

    I. Dormancy Breaking
        -Substitutes cold treatment effect
        -Flower bud break by GA₃ in Azalea
            Also Easter lily bulb cooling

    J. Pruning
        -Chemical pinching agent (i.e. Atrinal, Off-Shoot-O)
            Azalea

* K. Growth Retardants
-Height control in flower crops
Phosphon, B-9, A-Rest, Cycocel, *paclobutrazol (Bonzi)

          *Uniconozol (Sumagic) *long-lasting

        -Tree height control under utility lines
            Use of long-lasting growth retardants
            Bonzi, Sumagic

    L. Stress Protectants
        -Cold protection
        -Antitranspirants (ABA)
            Stomatal closure