10 RESEARCH REPORTS PNL Volume 13 1081
THE REACTION OF THE EARLY FLOWERING GENE efr UNDER SHORT-DAY CONDITIONS IN
THE PHYTOTRON
Gottschalk, W.
Institute of Genetics, University of Bonn, Federal Republic of Germai
Recombinant R 46C is homozygous for genes efr for earliness and bif-1
for dichotomous stem bifurcation. The plants form their first flowers at
the axil of the 4th to 6th foliage leaf and enter their flowering period about
10 days earlier than the mother variety 'Dippes Gelbe Viktoria' under field
conditions in West Germany. R 46C was crossed with other mutants and recom-
binants and a large number of different recombinant types is now available
homozygous for efr and other distinct mutant genes or gene groups of our
collection. Eighteen of these recombinant types were grown in a phytotron
under the following conditions:
Under these conditions, the plants of the initial line began flowering
46 days after sowing; the flowering period was 8 days. With regard to the
reaction of gene efr, two different criteria have to be considered: the in-
duction of flowering and the formation of fully developed flowers. Gene efr
shows a pleiotropic action as follows:
-Formation of floral buds at very low positions of the stem (=induction
of flowering).
-Many of these early buds, however, are not developed into flowers; they j
abort.
-Some of the lowest flowers, which develop fully, show certain anomalies I
in flower morphology.
Thus, early flower induction many plants of recombinant R 46C as well as of
most of the recombinants derived from it is not advantageous because of the
negative aspects of the pleiotropic pattern. One of the aims of our phyto-
tron investigations was to test whether these negative aspects can be reduced
or even eliminated by specific environmental conditions or by transferring
gene efr into specific genotypic backgrounds.
Floral induction occurred in all the genotypes homozygous for efr tested
during the normal stage of ontogenetic development, i.e. in the axil of the
4th to 6th foliage leaf. This indicates that the other mutant genes, combined
wifh efr, do not influence this physiological behavior. With regard to actual
flowering, however, the recombinants cultivated behaved very differently from
each other. In the plants of R 46C, the first fully opened flowers appeared
3S days after sowing; this was 11 days earlier than in the initial line. The
PNL Volume 13 1981
RESEARCH REPORTS
1 1
flowering period lasted 11 days which was somewhat longer than the initial
line. Three other recombinants, in which efr is combined with genes for
waxlessness and short internodes, showed the same behavior, indicating that
the genes involved do not influence the reaction of gene efr with regard
to this part of its pleiotropic pattern. Some mutant genes, however, influence
gene efr positively. Five recombinant types tested flowered two days and
another three types flowered even four to five days earlier than R 46C as
follows:
-RR 1041: slightly reduced internode length (short I), stem
bifurcated, sometimes weakly fasciated, early: 30 days
- R 869: very long internodes, slightly reduced chlorophyll
content, very weakly fasciated, early: 30 days
- R 864: very long internodes, non-fasciated, early: 31 days
In the field, these genotypes are linearly fasciated, but their stem is either
not fasciated or only slightly fasciated under the phytotron conditions men-
tioned above.
The opposite effect, i.e. flowering three to four days later than R46C,
was observed in four out of the 18 genotypes tested. Two genotypes flowered
extremely late:
-RR 1033: very long internodes, very weakly fasciated,
bifurcated, early flower induction: 56 days
- R 871: short internodes (short I), bifurcated, early
flower induction: 66 days
In R 871, only a few plants began flowering at 66 days; most of them either
failed to flower at all or flowered later in the two short-day trials in
which they were observed. Thus, these two genotypes are genetically early
due to the presence of gene efr, but in reality they are extremely late.
They are not only much later than their parental genotype R 46C but also
considerably later than the mother variety which begins flowering 46 days
after sowing.
Of particular interest, however, are two recombinant types which even
13 weeks after sowing did not have flowers or normally developed floral buds:
-R 20D long internodes, stem repeatedly bifurcated, early flower
induction
-R 20E very short internodes (short II), stem bifurcation, early
flower induction
Flower induction under the influence of gene efr took place in these two
genotypes, but the other mutant genes involved suppressed the development
of the minute floral buds into flowers thus influencing the pleiotropic action
of efr negatively. The recombinants R 20D and R 20E were selected in the
F2 of cross 489C x 46C. They differ from each other only with regard to their
internode lengths whereas both are homozygous for genes efr and bif-1. Thus,
it can be assumed that gene bif-1 for stem bifurcation is responsible for
the suppression of the action of gene efr in these recombinants.
The experiment shows the gene efr for earliness is highly influenced
both by other mutant genes of the genome and by specific environmental factors.
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