5 RESEARCH REPORTS PNL Volume 11 1979
A GENE FOR STEM BIFURCATION WITH FULL PENETRANCE
Gottschalk, W. Institute of Genetics, University of Bonn, West Germany
So far two polymeric genes, bif-1 and bif-2, are known to cause the
stems of peas to become dichotomously branched. Both these genes exhibit
an unstable penetrance depending on environmental factors as well as on the
genetic background. This instability reduces the agronomic value of the
two mutants which are of interest for pea breeding because of their favorable
yield potential. The penetrance of bif-1 was fully stabilized by mutant
genes responsible for small grains or long internodes. In both the recombi-
nant types, however, the positive effect of gene bif-1 is offset by the
negative effects of the other two genes.
After X-irradiation, mutant 37B was isolated and developed into a pure
line. The plants are somewhat shorter than the mother variety. They are
dichotomously branched in the upper part of the stem and have therefore
an increased number of pods per plant. The internode below the point of
stem bifurcation is fasciated. Seed size is normal. The mutant is morpholo-
gically identical with mutants 1201A and 157A homozygous for bif-1 and bif-2,
respectively. The only difference is that 37B is fully penetrant for the
new gene for stem bifurcation. In 1978, the following observations were made:
Mutant 1201A (bif-l/bif-1): penetrance = 62.8%
Mutant 157A Cbif-2/bif-2): penetrance = 39.2%
Mutant 37B : penetrance = 98.0%
Seed production of mutant 37B was about 15% better than that of the mother
variety.
The genetic relations between 37B and the other two bifurcated mutants
not yet clarified but the necessary crosses have been made.
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