XII. SEED PROPAGATION

- Joshua Machinga
What is a seed?

A seed is a dormant embryo; a living, resting plant whose life processes is operating very slowly. It maintains internal metabolic activity by consuming small amounts of energy from its endosperm wiithin a protective seed coat. It contains all the necessary instructions for the making of a new plant as well as a reserve supply of carbohydrates, fats, proteins, and minerals to nourish the dormant, encased seedling.

Kinds of seeds:

1)Dicots- majority of flowering plants. They have two seed leaves or cotyledons which store food for the young germinating plant for example-legumes, brassicas, and solanums.
2)Monocots- contain only one cotyledon. Food is stored in the endosperm tissue which surrounds the embryo, rather than leaves. For example- alliums and graminaceae.

Seed formation:

Though differing greatly in many respects, every flower contains the two essential ingredients for manufacturing seed.
Stamen-the male pollen bearing part of a plant. Containing a long thin stalk (filament) and pollen sacs (anthers).
Pistil-the female organ which receives pollen and nurtures future seeds. It contains a pollen receptive region (stigma) and a long, thin tube (style) leading from the stigma to a cavity (ovary) which contains one or more eggs (ovules).
Grains of pollen after landing on the stigma must travel to the ovary. In doing this, they form long tubes of tissues which grow cell by cell down through the style. A growth hormone (auxin) from the pollen causes the ovary to begin to enlarge once it‘s pollinated, even before actual fertilization occurs.

As a pollen tube approaches an egg, its tip bursts open and releases two sperm cells. One of these unites with an egg cell to produce the embryo (also called zygote). The other fuses with polar nuclei and develops into the endosperm. This dual process of sperm cells uniting with female cells is known as fertilization.

Types of pollination:
1.Self pollination- the flower is capable of pollinating itself with the aid of wind or insects. Pollen rarely travels from plant to plant. They all have COMPLETE flowers. A gardener may easily grow more than one variety at the same time, feeling confident that the next generation will resemble the parents. For extra precaution, simply plant another crop between different varieties of same vegetables. Includes: Solanums, Legumes, Wheat, and Lettuce.
2.Cross pollination- the pollen from one flower fertilize another flower, either on the same or on a different plant. Pollen is carried by wind or insects (usually bees). Some cross pollinated plants may be complete flowers yet be SELF-STERILE, thus requiring pollen from other plants for pollination.

Insect - bbrassicas, cucurbits, carrots, onions
Wind-maize, beets, swish chard, spinach

Many of these vegetables easily cross with other varieties of their family. So caution is should be taken if saving seed from them. Minimal distance is usually recommended to prevent undesired genetic combinations. If required separation is impossible, hand pollination may be applied. This involves caging and isolating plants you want to propagate. Understanding the pollination process of each of the vegetables you raise for seed is necessary for a successful seed saving program. For fertilization to take place, pollen must be of correct kind and it must arrive at the right time, when the plant’s parts are well enough developed to enable it to reproduce. Pollen from an unrelated species will be rejected. Some plants will not receive pollen from other plants in their species. Some flowers can discharge pollen before their stigma is ready to receive it, while others are simply sterile to their own pollen. Fertilization is fascinating, complex process posing an exciting challenge to anyone interested in seed production.

Why save seed?

There are many good reasons. Here are a few: economics, security, increased self reliance, production of plants best suited to your climate and conditions, preservation on genetic diversity, gaining of knowledge, personal satisfaction and adventure.

Careful selection:

Selection is the key to a successful seed saving program. It allows you not only to increase the quantity of garden plants but also to improve and refine their quality. Choose the superior plants whose seed will produce another generation with the same desirable characteristics. It is important to observe plants throughout their entire growing season to be able to rate their full performance. Take into consideration the WHOLE PLANT. For example save a seed from a tomato plant with many excellent fruits, not just one, or from African spider flower with vigorous growth and not too quick to set flower. As a general rule, one is advised to save seed from more than one plant in order to maintain a broader genetic base. Most seeds remain viable for several years, so it is necessary to save seed from every variety each season. Take into account those plants which may cross with each other and plan to save seeds from only one variety each season.

Some qualities to consider:

Flavor, yield, color, size, vigor, storage life, disease and insect resistance, drought tolerance, good germination, early bearing (fruits, heads, e.t.c.),late in bolting, quality of seed, texture, juiciness, e.t.c.