unexpected seed coat change

Beverly Erlebacher bae at cs.toronto.edu
Thu Jul 10 18:05:12 EST 1997


In article <33C477FA.1964 at northcoast.com>,
P Rose  <prose at northcoast.com> wrote:
>In 1993 I planted some 5000 Year Old Cave Beans.  I grew them in my
>garden, in the city, with no other bean plants around. 
>	I grew beans from the 1993 harvest in 1994.  When I harvested my 1994
>crop I noticed that some of the seed coats were different.  In '94 I
>grew some Scarlet Runner beans and they were in bloom at the same time
>as the Caves.  I thought the Runner was Phaseolus coccineus and would
>not cross with the Caves,  Phaseolus vulgairs. (Ref.  Seed to Seed by
>Suzanne Ashworth page 136)  The coats were unmistakably a cross between
>the 2 beans.  Upon further investigation, I discovered that the name
>runner was just a name and not the species.  
>	As you all know, seed coat is a product of the first generation and
>therefore would not show up until the second planting.  I am sure that
>the beans were not crossed in the 1993 growing.
>	I have since discussed this anomaly with both my Botany professor and
>the genetics professor at Humboldt State University.  They say that I
>had to have crossed the beans in '93 and they refuse to believe me.  I
>know that the beans were not crossed the first year and that something
>unusual has occurred....  I want to know what it is.  
>	I have 42 of the Caves that a friend grew from my '93 harvest in his
>garden in '94 separate from my "crossed" beans.  They do not exhibit the
>seed coat change.  I have 401 Caves with changed coats and 1011 Caves
>with no/(marginal) coat change and 53 runt beans.  I also have 78
>Scarlet Runner beans that were undoubtedly crossed with the Cave beans
>but show no seed coat change.  This is the total of my '94 harvest.  

It's very uncommon for P.vulgaris varieties to cross spontaneously, while
it's not at all uncommon for speckled beans to produce some heavily blotched
seeds due to some unspecified environmental conditions, possibly some aspect
of the weather.  There was some discussion of this in an issue of the magazine
of Seeds of Diversity (Heritage Seed Program), a Canadian organization similar
to the Seed Savers Exchange in the US.  The fact that your friend produced
normal beans from the same lot of seed supports an environmental rather than
genetic cause.  

I've read that spontaneous crossing in beans is about as common as spontaneous
mutation.  Some years I get a lot of blotched or almost solidly dark beans
from pure cultivars with speckled or romano-pattern seed coats.

>	  I want to design a research program to perhaps determine what
>happened genetically to the Caves.  I am writing because I need to find
>someone that has the expertise and is willing to help me design and
>carry out a research program. 

I suggest you grow separate rows of normal and 'changed' beans, and see
whether the distribution of seed coat pattern differs between the two groups.
See if your friend will do the same in his garden, where the conditions are
different.  If any of your beans resulted from a cross I would expect there
to be some difference in other plant characters than just seed coat pattern.

If you want to carry this out for another generation, I suggest you save the
seeds from each plant separately, and grow a row of each.

>	I don't know any people in the bean genetics business but I hope that
>someone can at least send me in some direction.  I have been sitting on
>this for 3 years and I am still positive that there is something unusual
>happening and am anxious to understand what it is.

I'm not a geneticist or botanist, but have been preserving vegetable varieties
for some years now.  I hope this helps.

>	Thank you for your time.  Any help that you can give me will be
>appreciated.

Btw, the best way to distinguish P.coccineus from P.vulgaris is that in
the former, the seed leaves stay in the ground but in the latter they
emerge with the shoot.  If the flowers are really red, it's P.coccineus,
but not all P.coccineus have red flowers.




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