THE REACTION OF THE EARLY FLOWERING GENE efr UNDER SHORT-DAY CONDITIONS IN THE PHYTOTRON

10 RESEARCH REPORTS PNL Volume 13 1081

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.