North American Fruit Explorers mailing list at ibiblio

[Lon Rombough <lonrom@hevanet.com>]

Most self-fertile plants are not totally so - crossing to other members of the species usually occurs at a low level.  Even when a plant is self-pollinating for many generations, there are a number of ways genetic variation can occur.  Mutations are the first thing, but we now know that genes can come into the plant in other ways, carried by viruses and bacteria, for instance.  There may be other mechanisms we haven't proven yet, too.  For instance, mycorrizal fungi can actually connect unrelated plants, and bacteria "travel" the fungal threads.  It seems possible that genes could be carried from unrelated plants by this "highway" albeit at a rather low level.  Still, in the course of eons a lot of transfer could take place this way.

Look at it this way.  There are old varieties of self-pollinating crops like beans that have been saved by home growers for generations.  If you grow out one of those varieties, you will usually find that while all the plants fit a general description of the variety, careful measurement and testing will show that there are actually many similar types that vary in a number of ways - higher or lower yielding, slight color differences, number of beans per pod, etc.  If you carefully select individuals and grow only their seed, the "new" selections will show differences from the "parent" variety more noticeably and they will be more uniform.  Yet, if you grew only that "type" from then on, after a number of generations you would begin to find small variations accumulating again.  How many generations?  Hard to say.  

Clear as mud now?
-Lon J. Rombough

Grapes, writing, consulting, my book, The Grape Grower, at http://www.bunchgrapes.com  Winner of the Garden Writers Association "Best Talent in Writing" award for 2003.
On Jan 27, 2005, at 9:45 AM, rob hamilton wrote:

This might be a little of topic, but I always wondered
how genetics worked in self fertile plants.  If a
plant is pollinated by the itself would that mean that
its childeren are clones of its parent, or would this
just allow recessive genes to be expressed?


--- Philip Stewart <philstewart24@yahoo.com> wrote:

> Part of hybrid vigor is a high level of
> heterozygosity, something no seed-propagated plant
> that has been "fixed" can ever have much of.  That
> said, there's no reason highly homozygous plants
> can't
> be plenty vigorous, assuming the deleterious
> recessive
> have been sorted out in the process.