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  • From: "Tradingpost" <tradingpost@lobo.net>
  • To: livingontheland@lists.ibiblio.org
  • Subject: [Livingontheland] Saving vegetable seeds: Factors to consider
  • Date: Mon, 09 Mar 2009 09:57:01 -0700


Saving vegetable seeds: Factors to consider
(Courtesy of Seed Programs, Inc.)
http://www.foodsresourcebank.org/resource_materials.asp?id=170
David A. Bender, Ph.D.

Dr. David Bender is Vice President-General Manager of Seed Programs Inc. He
has over 20 years of experience in vegetable physiology and production as
head of the vegetable research program at the Texas A&M Agricultural
Research and Extension Center in Lubbock, Texas. For more information on
saving seed, you can contact Dr. Bender at bender.spi@nts-online.net


The development of agriculture from prehistoric times to the present was
built on the selection, collection, and replanting of seeds from superior
plants. Even in a time of specialized commercial seed production, advanced
plant breeding, and emerging biotechnology, farmer-saved seed may be the
least expensive alternative for producing some crops. These techniques are
of particular interest to subsistence farmers worldwide, where economics or
logistics make it difficult to buy suitable planting seed. At the same
time, a number of biological and technological factors make saving seed of
many vegetables extremely challenging.


Type of plant

Seed is most easily saved from plants where the seed itself is eaten,
typically grains. These seeds are generally harvested when mature and dry,
and require relatively little processing prior to being replanted. Dry
beans, peas, and other vegetable legumes fit this category, but most other
vegetables are harvested for their fruits or vegetative parts, so special
effort is required to collect and dry seed.


Biennials

A number of vegetables, including most of the root and bulb crops (carrot,
beet, onion, leek), and the crucifer family (cabbage, broccoli, kale,
cauliflower), are biennial plants that require two years to produce seed.
These plants produce only vegetative growth the first year, and most
require a period of cold weather with temperatures between 0 and 7ºC to
induce seed stalks in the second year. Thus seed production is impossible
in tropical areas unless the bulbs or roots are refrigerated to simulate
natural chilling. Some tropical types may produce seed naturally, but
saving seed is difficult.


Hybrid seed

Hybrids are produced by crossing two carefully selected parent lines to
produce seed combining the best characteristics of each. Hybrids often
exhibit better productivity, uniformity, vigor, and pest resistance than
open pollinated varieties. However, seeds collected from these hybrids
produce plants with a variety of characteristics totally unlike their
hybrid parents. Saving seeds from hybrid plants is sure to result in
disappointment, and is not recommended.

Open pollinated seed

Plants which are allowed to pollinate naturally, without being manipulated
in any way, are referred to as open pollinated. Open pollinated varieties
result from repeated selection of superior plants from within the same line
until essentially identical genetically. However, within this group, we
must consider self pollination, and cross pollination. Some plants, such as
legumes and tomatoes, self pollinate naturally, and so seed collected from
these plants will produce plants identical to the parents. Others, such as
corn (maize) and vine crops (cucumber, watermelon), have their pollen
spread by wind or insects (usually bees). In these varieties, if the plant
is pollinated by other plants of the same variety, the resulting seed
should produce plants identical to their parents and be suitable for
saving, but if pollination was done by a different variety of the same
species, the resulting seed will produce plants with a mixture of
characteristics depending on both parents, and this will not be suitable
for saving.

Open pollinated vegetables produce true-to-type seed only when fertilized
by pollen of the same variety. It is easy to maintain the purity of
legumes, lettuce, tomatoes, and other self-pollinated vegetables. Pollen of
other vegetables is distributed by wind (beets, corn, spinach) or insects
(a majority of other vegetables), so in seed production care must be taken
to keep the flowers isolated from pollen of another variety of the same
vegetable. Isolation distance of at least 1,500 meters between different
varieties of the same species is recommended for all cross pollinated crops
which are to be harvested for seed. Cross pollination can also be prevented
by timing plantings so different varieties are not flowering at the same
time. Vine crops are particularly prone to cross pollination, and strange
types of squash and melons can be produced from seed produced where
different vine crops are grown in close proximity.


Seed maturity

Fully mature seed is required for subsequent germination and growth.
Pumpkins, winter squash, melons, tomatoes and some peppers contain mature
seed at normal harvest maturity. On the other hand, seeds of summer squash,
cucumbers, eggplant, snap beans, and green bell peppers are usually
immature at the stage these vegetables are eaten. When growing these
vegetables for seed it is necessary to leave the fruit on the plant well
beyond normal harvest maturity. Peas and beans must be kept on the plant
until pods and beans are dry.


Seed processing

Plants that produce seeds in a moist environment like a fruit often also
produce chemicals in their tissues that prevent the seed from germinating
while still on the plant. Thus it is essential that the seed be cleaned to
remove all fruit tissue to eliminate these inhibitors. For example, the
gelatinous tissue surrounding mature tomato seeds will completely inhibit
seed germination. Tomato seeds must be removed from the fruit, fermented
for several days, then carefully washed and dried. Other seeds must also be
washed to remove plant tissue and sugars that promote growth of molds and
fungi. It is critical that all seeds be thoroughly dried at moderate
temperatures and not exposed to direct sunlight.


Pest control

Seeds are an important source of food for some birds and insects. These
pests often will feed on seed before it is mature and dry, so the seed and
seed stalks may need to be protected until the seed is ready for harvest.


Seed-borne disease

Certain bacterial and viral diseases can be carried on seed from one year
to the next. A plant may become infected late in the season and still
produce a crop, but if the seed becomes infected on the plant, the disease
organisms may attack the seedling after germination and kill or seriously
stunt the subsequent crop. Proper sanitary practices are important to
prevent transmission of certain diseases to the next generation. Seed
should never be harvested and saved from plants which have symptoms of
disease.


Seed Storage

Once seed has been successfully produced and processed, it must be stored
properly to maintain germination and vigor. The seeds are living organisms,
and their life processes must be slowed as much as possible to minimize the
drain on food reserves in the seed and maintain the integrity of the seed
coat. Heat and moisture are the two greatest enemies of stored seed. Heat
speeds biological processes, depleting stored energy resources. Moisture
activates enzymes in the dormant seed, beginning the germination process.
This pre-germination activity depletes the energy reserves in the seed, and
weakens or kills the seed before planting.

To maintain viability and vigor from one planting season to the next, seed
must be kept cool, at least below 70º F (21º) and preferably cooler.
Seed must also be protected from moisture, including high humidity.
Desiccant materials can be included in the storage container to absorb
atmospheric moisture. If this is done, a barrier should separate the seed
from the desiccant so that the seed does not come in actual contact with
the chemical. Seed is attractive to insects and rodents, so it is also
important to save seed in a sealed container. A screw-top glass jar with a
rubber seal can exclude both moisture and pests.

Summary

Farmer-saved seed is often considered an important component of sustainable
agricultural development. Grains, which dry naturally, are grown in large
blocks, and generally have large stored energy reserves, lend themselves to
such a system. Vegetables encompass a wide range of plant families with a
variety of growing requirements, pollination strategies, seed types and
climatic adaptations. Their seeds are often small with small carbohydrate
reserves, and are thus less resistant to environmental influences. While
seeds of a few vegetables can be saved by the novice, it would be difficult
for most gardeners in developing countries to produce, process, and store
seed of the range of vegetables needed to supply adequate nutrition.
Greater sustainability might be achieved by increasing productivity of
gardens, allowing growers to sell some of their produce and buy good
quality seed every year.





  • [Livingontheland] Saving vegetable seeds: Factors to consider, Tradingpost, 03/09/2009

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