38 PNL Volume 14 1982 RESEARCH REPORTS
Loenning, W. E. Institute of Genetics, University of Bonn
Federal Republic of Germany
Another six thousand plants have been devoted to the problem of
fasciation and heterosis, leading to definitive results.
I. Six fasciated lines, each with a different stem length, were crossed
to a common line, 'Dippes Gelbe Viktoria' (non-fasciated):
a) 489 C x mother variety Dippes Gelbe Viktoria (DGV)
b) 251 A x DGV
c) R 710 x DGV
d) R 875 x DGV
e) Mutant 1/74 (of Vasileva's collection) x DGV
f) Mutant VI/10 (of Vasileva's collection) x DGV
Dominance for superior length was evidenced by 3:1 segregations in
F3 and backcrosses of long, nonfasciated recombinants, derived from the
heterotic hybrids, with Dippes Gelbe Viktoria (including segregations).
Since the degree of hybrid vigor varied with the fasciated lines used,
it can be concluded that the dominant genes for length were contributed
by the fasciated parents. The following facts show that the fasciata
genes themselves are responsible for the suppression of the dominant
genes in the fasciated lines:
a) Originally long lines are shortened by fasciation. The
original length can be regained by recombination. Example: F1
mutant 1/74 x R 46 C was as long as mutant's 1/74 mother
variety 'Ramonski', the length of which could be regained by
b) The recessive fasciata genes cause growth anomalies, shortening
several internodes but never elongating them in comparison with
the long recombinants.
c) Heterozygotes segregating for only one fasciata gene are as
long as the related nonfasciated homozygous lines but the fas-
ciated lines are shorter.
d) Full length has only been regained in nonfasciated
No heterotic stimulus of heterozygous fasciata genes could be found
by the different methods applied (1).
II. Seed production, a polygenic trait, showed many interactions with
genes for other characters, leading to a more complicated situation.
There is no doubt, however, that seed production can also be affected
strongly by fasciation. Three different cases can be cited at present,
where the high seed production of the hybrids has been fixed in
recombinants: R 710 x DGV, Mut 1/74 x DGV, and, in part, 478 C x DGV.
For the latter, the results were contradictory during the last two
years. In 1980 a recombinant was as productive as the hybrid; in 1981
the latter surpassed the former. Crossing highly reproductive recom-
binants (derived from the heterotic hybrids) with DGV has led to hybrids
which compare favorably with the better parent.
All things considered, the investigation of some 15,500 plants
(including more than 40 different hybrid stocks with replication of a
PNL Volume 14
few outstanding cases and segregation and selection from F2 - F5, with
backcrosses and their segregations) during the last three and a half
years has clearly pointed to recessive epistasis and dominance as the
main causes of the heterosis observed in crosses of fasciated with non-
fasciated lines.

1. Loenning, W. E. 1982. Theor. Appl. Genet, (in press).