Sexual Propagation

plant

Seeds

The uniting of the pollen (male) with the egg (female) to make a seed is called sexual propagation. The seed consists of three parts: the outer coat, which provides protection; the endosperm provides a food source; and the embryo, the young plant itself. Once a seed is placed in a favorable environment and matured, it will germinate, or begin growing actively.

For quality plants, it’s very important to start with good quality seed from a reliable dealer.  Also, selection of a variety of size, color, and habit of growth will better provide the desired result.  Adaptation in your choices given your specific area will allow for the plants to mature prior to an early frost.  Many new vegetable and flower varieties are actually hybrids, which are often more expensive than open pollinated types, but are able to give more vigor, uniformity, and a better production, sometimes even featuring a specific disease resistance.

Although some seeds can keep for several years if stored properly, most advise to only purchase enough seed for the current year.  Quality seed will not contain seed of any other crop, weeds, seeds, or other debris, and printing on the packet will indicate essential information about the mix.  This information could include the year for which the seeds were packaged, and germination percentage you may typically expect, and even could include notes about any chemical seed treatment.  If seeds are obtained long before the actual sowing date or are surplus seeds, keep them cool and dry, often laminated foil packets can help ensure dry storage.  Paper packets are best kept in tightly closed containers and maintained around 40◦F. in a low humidity.  The door shelves in a refrigerator work well. Seed which is saved from previous gardens is the result of pollination by insects or other natural agents and may not produce plants exactly like the parents.

Germination

There are a few internal requirements that have to be met prior to germination beginning.  There must be a mature embryo, a large enough endosperm to sustain the embryo throughout germination, and enough hormones to initiate the entire process.  Normally, don’t expect more than 65% to 80% of the new seeds to germinate, and of those that do expect roughly 60% to 75% to produce satisfactorily.  The four environmental factors which affect germination: water, oxygen, light, and heat.

The imbibition or absorption of water is the first step in germination.  While seeds have the ability to absorb large amounts of water because of the seed coat, how much water is available will affect the uptake of water.  Sufficient and regular water supply is important to ensure germination.  Once the process is started, a dry period can kill the embryo.

Light can stimulate or inhibit germination of some types of seed.  Light reaction can be a complicated process.  Some crops which have a requirement for light to assist seed germination are ageratum, begonia, browallia, impatiens, lettuce, and petunia.  However, peas, beans, calendula, centaurea, annual phlox, verbena, and vinca will germinate best in the dark, and other plants are not specific at all.  Seed catalogs and seed packets often list germination or cultural tips for individual varieties.  When sowing a seed which requires light, leave them on the soil surface.  If they are to be covered at all, cover them lightly with fine peat moss or fine vermiculite.  These two materials, if not applied too heavily, will permit some light to reach the seed and will not limit germination.  Fluorescent light fixtures, suspended 6 to 12 inches above the seed for 16 hours a day can provide supplemental light for starting in the home.  High intensity lights provide more light over the course of the day and enhance the quality of seedlings.  While they are worth the investment if you want to grow indoors, they are more expensive.

In all viable seed, respiration takes place. In dormant seed the respiration is low but there is still oxygen required.  Because the rate increases, the substrate in which the seeds are placed should be loose and well-aerated.  Limited or reduced oxygen supply during germination can cause severe retardation or inhibited results.

A favorable temperature is a vital requirement of germination.  Not only does it affect the percentage but also the rate at which germination occurs.  Some seeds germinate over a wide range of temperatures, but others have a very narrow range available.  Some have minimum, maximum, or optimum temperatures for germination.  Tomato seeds, for example, have a minimum temperature of 50 degrees F., a maximum of 95 degrees, and an optimum germination temperature of around 80 degrees.  When temperatures are listed, they are usually the optimum temperatures unless otherwise specified.  As a general rule, 65 to 75 degrees F. is best for most plants.  This often means the germination flats may have to be placed in special chambers or on radiators, heating cables, or heating mats to maintain optimum temperature.  Maintaining proper substrate temperature for maximum germination percentages is vital and can’t be over-stated, and these temperatures should be maintained 24 hours a day.

Sources

http://umaine.edu/propogation

http://www.cropsreview.com/sexual-propagation.html

2017-07-20T12:11:49+00:00