The X-ray production of Seed of autodiploid "beneficial" mutations in
quantitative traits.<p>
    
Mertens, T. R.<p>

Seed of autodiploid (2n exhaploid) and highly inbred lines was X-irradiated
and R1 plants were backcrossed to unirradiated control plants of the same
line.  The resulting backcross progenies were grown together with control
plants in a replicated experiment.  Individual plants were scored for three
different measures of earliness, a trait which shows a dominance type of
heterosis (Burdick, Genetics 29(1954): 488-505).<p>
     
Induced mutations that have a beneficial effect on growth rate in heterozygous
condition should stand a good chance of being incladed in gametes of the R1
plant.  Deleterious mutations might well be eliminated by "intrasomatic
selection".  Backcrossing the R1 to an unirradiated control increases the
frequency of the induced beneficial gene, so that it is more readily
detectable.  This technique is suitable for detecting physiologically
beneficial mutations having an effect in the heterozygous condition.<p>
     
Two backcross progenies were produced that appear to be earlier than their
respective controls:<p>

<pre>




                         Backcross       Trait Measured #
           Dose          Progenv       I       II      III
____________________________________________________________
Control                   018-1       65.1    69.6    100.1
(Red Cherry inbred)
6,000 r X-ray             018-21      61.1    66.2     96.3
____________________________________________________________
Control                   228-1       67.2    74.0    100.3
(L. Pimpinellifolium
autodiploid)             
48,000 r X-ray            228-8       62.8*   70.0**   96.8*
____________________________________________________________

# I Mean days to first flower, first infloresence.
 II Mean days to first flower, second inflorescence.  
III Mean days to firstripe fruit.
* Significantly different from control by Duncan-Bonner test,
5% level.
** Highly significantly different from control by
Duncan-Bonner test,
     1% level.

</pre>
Line 018-21 was included in a large experiment involving 59 entries so that
the chance of finding statistical significance was very low.  However, the
fact that the plot means (data not given) of line 21 were earlier than any of
the 18 control plot means in the experiment indicated that this line is
actually earlier.  The twoo early progenies recovered in these experiments
were extracted from 3% of the 65 R1 plants from which backcross progenies were
obtained and tested.<p>
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