permaculture

[Jack Rowe <jackrowe@compuserve.com>]

For UteB and others wanting to save seed from vegetable plants, here are a
couple notes relating to population size vis-a-vis saving seed, esp. from
corn [taken from Seed Saving Handbook, Rowe, Seeds of Texas Seed Exchange]:

"Among plants which reproduce sexually, collecting seeds from too-few
parents can result in dangerous narrowing of a variety's genetic base. The
resultant weakening of the variety is called "inbreeding depression". Since
each individual plant typically does not contain all the available genes
belonging to the variety, some minimum number of plants is needed in order
to maintain the diversity and vigor of the variety.

The degree of danger from inbreeding depression, and the number of parent
plants needed to avoid it, depends on several factors. One factor is the
variability of the variety—the greater the variation between individual
plants in a population, the more plants will be needed to preserve their
collective genetic base. 

Another factor is the method by which pollination is accomplished between
parent plants within the variety. As few as one or several plants may
suffice for self-pollinated plants such as tomatoes or beans, since these
plants do not normally rely on cross-pollination between different plants
to maintain a healthy degree of genetic variability.
Partially-self-pollinated plants, such as peppers, lettuces, etc., do not
rely heavily on cross-pollination and can maintain their genetic health
with a relatively-small number of parent plants, say 10 or more. 

A plant notable for needing a particularly-large parent population for
long-term breeding health is corn, which needs at least 200 parent plants
to produce healthy seed batches."

[And, specific to corn]:

"Another important consideration in growing corn for seed is the size of
the planting. Corn represents an extreme example of the necessity for
growing a large enough number of plants to avoid inbreeding depression.
Corn requires a parent population of 200 or more plants for continuing
vitality of a plant population, with seed collected from as many of those
plants as possible. A healthy planting of seed-corn should start with 300
or so seeds, and care should be taken not to let a planting fall to too few
plants for continued genetic vitality. One idea for broadening an existing
seed batch's genetic base is to mix it with the same variety seed grown by
different growers."

Be sure to follow these guidelines when growing corn! Good Luck,

Jack