Intrasomatic selection after seed irradiation.<p>

Burdick, A.  B.<p>

Much evidence has led us to suspect that when seed is treated with irradiation
a variety of mutations is produced in the different cells of the seed meristem
and that when a plant develops from this seed there is a certain amount of
competition among the lineages of the original irradiated cells such that the
resulting plant is a mosaic of various kinds of mutant and normal tissue.  If
this were so it would mean that mutations recovered from such plants would
have undergone a certain amount of selection for high heterozygous viability.
We have been able to obtain some direct evidence on this point.  We irradiated
seed with 10,000 r and kept an equal amount of untreated seed for control.  We
harvested flowers for pollen abortion determinations and fruit for seedling
mutation determinations from each of the first three inflorescences (which
occur in linear order on the main axis) of these plants. The essential items
of data are given in Table 1.<p>

The data clearly indicate that the R\1 plant is, indeed, a mosaic of
mutant-heterozygous and normal tissue with respect to these seedling
mutations.  This is represented by the recovery of a mutation from one of the
three inflorescences but not from the other two.<p>

We did, however, recover the same mutation from two or three inflorescences of
certain plants. (Our lethal mutations are determined on the basis of
germination percentage of R\2 seed and, therefore, we expect to see what
appear to be lethal mutations in the control progenies.  These seldom turn out
to be actual mutations in the control progenies but represent what might be
considered the error in frequency determination in the treated material.)<p>

We obtained R\1 pollen-abortion data (to detect irradiation induced
rearrangements and sectoring thereof) from the same inflorescences from which
seed were obtained and the sectoring pattern was similar to that shown for
seedling mutations.<p>

These evidences clearly show that the R\1 plant following seed irradiation is
almost always a mosaic of mutant and-non-mutant tissue, perhaps a mosaic of
several different kinds of mutant tissue.<p>

<pre>
Table 1.  R\2 seedling mutations recovered from different
          inflorescences of R\1 tomato plants; control and 
          10,000 r-treated groups.

________________________________________________________________
               Number of R\1 plants with a mutation
               in the following inflorescence(s):
Kind of Mut.   1    2    3   1,2  1,3  2,3  1,2,3    Total
________________________________________________________________
                              
                      10,000 r-treated

Lethal         8    2    5    1    -    1     1       18
Chlorophyll    1    1    3    -    -    1     1        7
Morphological  1    -    -    -    -    -     -        1
No Mutation                                           19
Total                                                 45
                        Control

Lethal         4    1    -    -    -    1     -        6
Chloriphyll    -    -    -    -    -    -     -        0
Morphological  -    -    -    -    -    -     -        0
No Mutation                                           32
Total                                                 38

</pre>






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