PNL Volume 11 1979 RESEARCH REPORTS 10
Gottschalk, W. Institute of Genetics, Bonn, Germany
In an M2 family following X-irradiation, some mutant plants arose which
were unable to produce flowers (mutant 172 of our collection). The plants
showed normal behavior and development with regard to height, growth rate,
and physiological activity, but instead of producing inflorescences, they
form lateral branches with extremely shortened internodes. The growing points
of these lateral branches (and of the main growing point of the stem) remain
active, producing leaves and internodes, while the plants of the mother
variety are long since mature. Plants remain alive in the field until killed
by frost or by heavy mildew attack towards the end of the growing season.
When cultivated in the greenhouse, they survived for two years until they
succumbed to disease. Surely they would have survived longer under optimal
greenhouse conditions without having formed any flowers. We have maintained
this mutant type over a period of 11 generations by propagating plants hetero-
zygous for the mutant gene. During this time, with hundreds of plants having
been grown, not a single flower was formed.
Histological studies revealed that the growing points of the main stem
and the lateral branches remain mitotically active, permanently producing
new cell material which differentiates to somatic tissues. Differentiation
of floral buds does not occur. Nor did cultivation of the plants in the
greenhouse under different photoperiodic conditions induce flower formation.
Thus, the behavior of the mutant seems not to be due to a specific photo-
periodic requirement. Presumably an enzyme(s) necessary for the transition
of the plants from the vegetative to the reproductive stage is lacking.
Mutant 172 arose by X-irradiation. What appears to be the same mutant
was selected in neutron experiments. It is like 172 in all respects, but
heterozygous plants of the two sources have not yet been crossed to verify
their identity. The recessive gene in Mutant 172 is designated "veg".