icon
icon

Everything About Seed Germination

mjactivist

hIGH, iM hIGH
Sep 27, 2006
231
46
0
34
#1
SEED GERMINATION-
Necessary Factors for Germination:
There are several factors affecting seed germination. First and foremost, seed must be viable meaning it must be capable of germination. Proper storage of seed also factors in on seed germination. Seed must be placed in proper environmental conditions - optimal moisture, proper temperature, and ample oxygen must all be considered. Light also may or may not be needed for seed germination. Finally, a seed's ability to overcome primary dormancy will effect seed germination. If these conditions are met, germination can take place.
Seed germination follows three phases according to physiological processes.

Stages of Germination-
Phase One - Activation:
Imbibition of water is the first process that occurs during activation. Once imbibition of water has occurred, activation or the synthesis of enzymes is initiated. These enzymes function in the breaking down of storage material within the seed into simpler compounds such as sugars, which are utilized by the embryo for germination. Other enzymes activated during respiration start breaking down sugars for the production of energy that the developing seedling can use for growth and development. At the end of activation cell elongation and radicle emergence occur - the first visible (outward) sign that germination has commenced.
Phase Two - Digestion and Translocation:
During digestion and translocation, enzymes that were synthesized or activated begin to break down storage material within the seed into simple compounds, which are translocated, to the embryo axis or plumule and root or radicle. The plumule will grow and develop as cells elongate and divide.
Phase Three - Seedling Growth:
The germinating seed continues to undergo metabolic changes culminating into a seedling. Seedling growth can be of two types: epigeous germination or hypogeous germination. Both refer to the position of the cotyledons during germination. In epigeous germination (epi - Latin meaning above or beyond), the cotyledons are pushed above the soil surface Beans and other legumes are examples. In hypogeous germination (hypo - Latin meaning under), the cotyledons as well as most of the seed remains underground with only the shoot emerging from the soil surface.

DORMANCY-
Primary Dormancy:
Most seed does not germinate immediately but rather undergoes or is under the influence of some type of primary dormancy present to delay initial seed germination. Seed dormancy in nature usually exists to delay germination until favorable environmental conditions are present for seed germination, growth and development.
From a plant propagator's viewpoint, primary dormancy is a condition that is present when a viable seed does not germinate under favorable conditions. There are many kinds of primary dormancy discussed in detail below.
Types of Primary Dormancy:
Causes of primary dormancy can involve the seed coat, chemicals within the seed, morphological stages of the seed, physiological requirements, temperature requirements or a combination of the above
Seed Coat:
Seed dormancy may be due to the presence of the seed coat. This can be broken down into two parts--physical and mechanical. Physical is by far the most abundant type of seed coat dormancy. Basically, physical seed coat dormancy prevents the embryo inside from imbibing water thus the seed coat is impervious to the uptake of water. In mechanical dormancy, the seed coat is too strong to allow the germinating embryo inside to break through. The seed coat is mechanically too strong to allow the radicle to emerge. In order to overcome both these types of dormancy, scarification (softening or injury of the seed coat) must be accomplished.
Chemical:
Another type of primary dormancy is chemical dormancy. With chemical dormancy, chemicals present within the seed coat inhibit germination. Chemical dormancy is removed by leaching or exposing the seed to copious amounts of water over a period of time.
Morphological:
A third type of primary dormancy in seed is morphological dormancy where the embryo is immature or not fully developed at time of fruit maturity. Morphological dormancy is overcome by a period of after-ripening by exposing immature seed to optimum conditions after harvest, allowing the embryo to fully develop. Generally, cool, moist conditions in the range of 13º-18º C (55º-65º F; not as cool as in stratification) are optimum for after-ripening to overcome morphological dormancy.
Physiological or Intermediate:
Physiological dormancy is a result of seed requiring some type of physiological condition to be met in order to germinate. Some seeds when first mature need to dry down or dehydrate before they are capable of germination. Other seeds need exposure to light for germination to occur. These are for brief periods. Brief exposure to treatments such as light, dehydration, or slight chilling treatments in the absence of moisture can help overcome physiological or intermediate dormancy.
Deep Dormancy:
Temperate plants typically exhibit some type of deep dormancy, staying dormant until conditions are favorable for germination. Generally an accumulation over time of chilling is required to overcome deep dormancy. Seed exhibiting deep dormancy are adapted so that during the first periods of warmth, seed will not germinate immediately until chilling requirements (one to three months of chilling temperatures) have been met. Without deep dormancy, seeds germinating in warm weather run the risk of being killed by rapidly changing freezing weather associated with early spring. This chilling process is termed stratification. Artificial stratification treatments may be applied to seed by the plant propagator where seed are placed in chilled conditions until radicle emergence occurs.
Double Dormancy:
Double dormancy is any combination of the above factors. For example, there may be seed coat dormancy in combination with deep dormancy. In this case, seed coat dormancy must be overcome first before overcoming deep dormancy. A combination of scarification and stratification would be applied by the plants propagator in this example.
Secondary Dormancy:
Secondary dormancy factors can also influence seed dormancy. Secondary dormancy prevents germination of a seed after imbibition of water has occurred. The activation phase has started but does not progress. Causes of secondary dormancy include temperature extremes prolonged darkness, or prolonged light. Water stress, dry conditions, or oxygen extremes--anoxia or hypoxia (too much or too little oxygen) can also induce secondary dormancy.
OTHER FACTORS AFFECTING GERMINATION:
Environmental factors other than primary dormancy can affect germination and include temperature, amount of oxygen, and light. Some of these conditions may be considered secondary dormancy factors.
Temperature:
Plants may be classified into basically four groups in regard to the temperatures at which their seeds germinate. The first type is cool temperature tolerant plants, which represent most plants that are native to temperate zones. Seed of cool temperature tolerant plants can germinate at temperatures as low as 4.5º C (40º F) but prefer optimal temperature in in the range of 25º-30º C (77º-86º F) for germination to occur.
The second group of plants require cool temperatures for seed germination. Seeds of this type originate from cool season plants, most of that are native to the Mediterranean or Mediterranean type climates. These climates usually have hot, dry summers and cool moist winters. In terms of seed germination, it is favorable for seed to germinate in winter under cool moist conditions rather than during the hot, dry summer. Thus plants of this group posses mechanisms that prevent their seed from germinating when soil temperatures exceed 25º (77º F).
The third group of plants require warm temperatures in order for seed germination to take place. Seed of this type generally will not germinate unless soil temperatures are 10-15º C (50º-60º F) and show visible signs of chilling injury if germination at lower temperatures occurs. Seedlings afflicted with chilling injury may be chlorotic, slow growing and accompanied by disease problems. Some examples of warm temperature requiring seeds include cotton and corn. Most of these plants are tropical in origin and adapted to regions where soil temperatures do not get very low.
The fourth group of plants require an alternating diurnal cycle of temperatures to initiate germinate. Basically, this involves alternating temperatures on the surface of the soil of warmth provided by sunlight during the day and cooling of soils at night through radiant heat loss.
Oxygen:
Another factor affecting germination is concentration of oxygen available to the seed. Germinating seed are very metabolically active - respiration is occurring at high rates breaking down storage materials and sugars and converting them to other forms more useful to the seed. This all requires oxygen, which is thus necessary for seed germination. Oxygen may be limiting in heavy soils such as clay or flooded conditions, which in turn will affect seed germination.
Light:
Another factor affecting germination in some types of seeds is light. Epiphytes are examples of plants that require light in order for seed to germinate. Many epiphytic plants posses seeds that are light sensitive, meaning that if exposed to darkness for extended periods, viability is lost. In other words, light must be present in order for these seeds to germinate.
Light may also be a factor in physiological dormancy. Many plants having very small seeds require exposure to light to overcome physiological dormancy. Seed of this type must be on or near the soil surface in order to germinate. Lettuce is an example of a plant that generally needs exposure to light in order to germinate. Conifers as well need light requirements to satisfy seed germination.
Conversely, there are plants that need darkness in order for their seed to germinate. This is related to soil depth. Cacti and other desert plants are examples and are adapted so that germination only occurs in total darkness deep within the soil. The deeper the seed is in soil the closer it is in proximity to moisture, which is a requirement for survival in desert environments.
Photoperiod or changes in day length can also affect germination. Certain seeds, especially those of some woody, temperate species require particular day lengths before germination can occur.

Thanks to Texas Tech, Pistils, and LIzWier for sharing info
L8
MJ
 
Likes: 48martin

raymont

WT Regular
May 4, 2010
123
3
0
61
#3
Stuck mine in a plastic cup with fox forest. 2 inches on day 4. Good seed I guess. Nuttin special here.