GENE FOR STEM BIFURCATION WITH FULL PENETRANCE

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.