I. GERMINATION PROCESS

    Stage 1: Activation

                        a. Imbibition of water
                                80-120 % Dry weight
                        b. Synthesis of Enzymes

                Cell Division / Elongation (Embryo)

    Stage 2: Digestion and Translocation

                        -Breakdown of storage food
                        -Transport to growing points

    Stage 3: Seedling Growth

                        -Radicle growth to form roots
                        -Plumule growth to form shoot

                    -What are epicotyl, hypocotyl?
                        -Difference between epigeous, hypogeous germinations?
 

II. SEED QUALITY

    A. Seed Viability
            -Germination
            -Germination percentage

    B. Seed Vigor
            -Speed of germination
            -Seedling sizes
 

III. DORMANCY

       A temporary suspension of visible growth from a structure containing a meristem (bud, seed)

     Dormancy vs. quiescence (immediately germinated when environment is favorable)
     Ecodormancy-dormancy due to unsuitable environment
     Paradormancy- dormancy due to physical or biological factors externally imposed -ex. seed coat, apical dominance

    A. Primary Seed Dormancy
            1) Seed Coat Dormancy
                -physical dormancy--- due to impervious seed coat
                        seed coat of palisade-like macrosclereid cells
                        i.e. woody legumes (Acacia, Robinia, Sophora)
                        overcome by scarification
                -mechanical dormancy-- due to mechanical restriction of embryo expansion
                        i.e. walnut, peaches

            2) Chemical Dormancy
                -caused by germination inhibitor chemicals
                        i.e. fleshy fruits (citrus, grapes, tomatoes), huls of dry fruits
                                phenols, coumarins, abscisic acid, etc.
            3) Morphological Dormancy
                -Embryo not fully developed---> Enlargement required
                    after water imbibition at high temperature
                -Rudimentary embryos (proembryo-like) -Anemone, poppy
                -Undeveloped embryos (torpedo-like) -carrot, cyclamen, gentian palms---overcome by high temp, GA treatment
                -Orchids (undeveloped seed, little endosperm)- use aseptic methods
            4) Physiological Dormancy
                -General type of primary dormancy
                    physiological dormancy often disappears during storage for 1-6 months (cereals, grass, vegetable, flowers)
                -Thermodormancy- Germination inhibited by:    High temp (>25 C )-Lettuce, celery
                                                                                        Low temp (<10 C)-Cocklebur, amaranth
                -Photodormancy- Germination sensitive to light
                                                    ex. pansy--better in dark
            5) Physiologically Deep Dormancy (Embryo Dormancy)
                -Dormancy controlled by embryo (internal)
                -Occurs in trees, shrubs, herbaceous plants of temperate zone
                -Requires stratification (moist chilling) for 1-3 months
                        After-ripening completes during stratification
                 Stratification requires:
                   a) moisture
                   b) aeration
                   c) chilling temp
                   d) time
            6) Epicotyl Dormancy
                -epicotyl growth, after gemination, is inhibited

            7) Double Dormancy
                -more than one dormancy involved
                    seed coat + physiological dormancies

    B. Secondary Seed Dormancy
            -Inhibition of Germination, after primary dormancy is eliminated, by unfavorable environmental conditions
            -Usually by temperature extremes, dark (skotodormancy), or prolonged white light (photodormancy)

    C. Chemical Control of Dorman

            1) Gibberellins (GA₃, GA₄₊₇)                               
                -promotes germination
                -relieves physiological dormancy, photo-, thermodormancy
                -activation of enzyme synthesis, substrate mobilization

            2) Abscisic Acid (ABA)
                -prevents 'precocious germination' 
                -induced primary dormancy
                -accumulates as fruit matures, preventing vivipary
                -decreases during stratification
                -ABA application inhibits germination of non-dormant seed

            3) Cytokinins

                -offset ABA activity
                -play a 'permissive' role in germination by helping GA function

                  Zeatin- natural
                   Kin, BAP- synthetic

            4) Ethylene
                - promotes germination in some see
                - produced by germinating seedlings (bean)        
            5) Other chemicals
                -potassium nitrate---stimulates germination 
                -Thiourea-- overcomes dormancy in prunus

IV. ENVIRONMENTAL FACTORS ON GERMINATION

    A. Water (moisture)

            -important for osmotic adjustment
                 osmotic priming (use NaCl, KNO₃)
            -soaking (O₂ needed, aeration)
            -fluid drilling

    B. Temperature

            -cool temp requiring---- lettuce, onion, coleus, cyclamen, primula  (all fail to germinate at > 25° C or 77° F)
            -warm temp requiring
                Asparagus, sweetcorn, tomato (no germination below 10° C, 50° F)
                eggplant, bean, pepper (no germination < 15° C)
                cotton, sorghum (chilling injury at <10° C)
            -alternating temperature
                some seeds prefer diurnal temperature fluxuation  (10°C, 18°F)

    C. Aeration

            -O₂ required for respiration during dermination
            -rate of O₂ uptake = measure of vigor

    D. Light
            -Absolutely light requiring -some epiphytes, mistletoe
            -most seeds germinate in both light and dark
            -light inhibited--- Allium, phlox, Amaranthus
            -light quality
                    phytochrome responses
                        red light requiring (P_r, 660-760 nm)
                        far-red light requiring (P_fr, 760-800nm)