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[seed-saving] Cross-pollination in flower varieties



Ute,

I think the Calendulas will cross, and being Compositae are bee pollinated
so up to a mile might be needed for isolation. 1/4 mile is a more probable
useful figure. Bees travel farther to forage in areas where available
forage vegetation is sparse. . . two plantings in a densely-vegetated area
separated by a 100-foot field of yellow flowers might be perfectly safe.
Bee foraging patterns are complex, and territories don't overlap so under
some circumstances (barriers to bee travel, flight patterns of bees,
territory boundaries) a very short distance could be enough for isolation.
Pretty vague and difficult to quantify or give definite boundaries, plus
the bee populations could change from one year to another.

Larger plantings are safer from crossing, too, since individual bees will
likely get their foraging fill in one group of plants before needing to
venture into a neighboring planting. Also, in larger plantings, seeds taken
from nearer the center of the planting will be purer. These facts are true
of wind-pollinated plants, too.

A little crossing below the threshold of major changes tends to invigorate
a given population, so absolute purity is not always a desirable thing.
Take dogs and royalty as good examples of this fact. Fairly uniform
characteristics can be maintained by 'roguing', or preventing 'off types'
from flowering after their 'offness' is noticed. Roguing is fairly common
among pepper growers, who sort-of-safely ignore adequate isolation
distances and then later take advantage of the tendency for peppers to
cross at only 5% - 10% or so, being self-fertile and mostly
self-pollinating. Taking over a group of peppers not carefully isolated by
their previous caretaker for about 3 years, I found only one variety which
was thoroughly confused after this period of time. Most had maybe 15% off
types. Furthermore, there were some interesting 'new' types among the
peppers I ended up with and some good selection experiments could have been
carried out. If you've grown sunflowers you probably know that the
Composites can cross a lot more rapidly than this, though.

For truer maintenance of characteristics, take advantage of properly-dried
seeds' storage capabilities and just grow only one variety from each
species each year in an alternating cycle. Or use 'time isolation' if
you've a long growing season, letting the earlier variety produce a good
seed crop before the second is flowering. 

Any opinions I'd have on the Nasturtiums would be even more speculative, so
I'll refrain from wilder guesses. Seed trade associations might have access
to the information you seek -- you'd likely have to be a member to pry it
from them (e.g. American Seed Trade Association,
http://www.amseed.com/index.html; Canadian Seed Trade Association,
http://cdnseed.org/index.html).

Good luck, please let us know any interesting results!

Jack Rowe
Seeds of Texas Seed Exchange
http://csf.colorado.edu/perma/stse/

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