1022-7954/01/3702- $25.00 © 2001
Russian Journal of Genetics, Vol. 37, No. 2, 2001, pp. 150–155. Translated from Genetika, Vol. 37, No. 2, 2001, pp. 207–214.
Original Russian Text Copyright © 2001 by Konovalov.
Homozygosity for a mutant gene commonly results
in a speciﬁc mutant phenotype which differs from the
wild type. Many mutant genes negatively affect viabil-
ity, and homozygous mutants are phenotypically
weaker. However, selection for viability allows pheno-
typic restoration of the wild type.
mutant allele of the alcohol dehydroge-
nase (ADH) gene is lethal in homozygous sugar beet
seedlings . Microgametophyte selection for higher
frequency of the mutant allele in progeny of individual
plants has yielded viable mutant homozygotes
plants display a higher combining ability
as compared with heterozygotes
Owing to the higher combining ability of these
plants, their hybrids exhibit better characteristics com-
pared with hybrids of plants with other genotypes
(wild-type homozygotes and heterozygotes). Among
other traits, germinating ability of seeds, length and
weight of one-week-old seedlings, chlorophyll content
in leaves, and root weight at the end of vegetation (an
integral parameter of productivity) have been studied
. The analysis showed that length and weight of one-
week-old seedlings are associated with ﬁnal root
weight and can be used as independent parameters to
study the combining ability in sugar beet.
Upon selection, viable mutant homozygotes
obtained in F
were markedly exceeded in development
by plants of the other genotypes and expressed a spe-
ciﬁc “mutant” phenotype. Starting from F
, plants that
only slightly differed from wild-type ones were
detected among mutant homozygotes. Thus, the viabil-
ity of homozygotes for the mutant allele was restored in
two steps: the “mutant” phenotype was formed ﬁrst
and, then, the viability was restored to the normal level.
Hence, the question is whether the process of pheno-
typic restoration affects the combining ability.
, we obtained 11 mutant homozygotes varying
in phenotype from clearly mutant to nearly wide-type.
In the present study, we report the data on their combin-
ing ability which was examined in progeny of crosses
with unrelated genotypes.
MATERIALS AND METHODS
homozygotes that varied in pheno-
type from clearly mutant to nearly wild-type were
planted on an isolated plot. The plants were cross-pol-
linated and seeds were obtained in these inbred crosses.
At the end of vegetation, total biomass was esti-
mated by weighting each individual plant together with
the root and seeds, and fertility was determined as the
total number of seeds per plant.
To estimate the individual combining ability, F
hybrids were obtained by crossing each mutant
homozygote with an unrelated plant. For this purpose,
12 side shoots were isolated on a male-sterile plant
before ﬂowering. The pollen was obtained from each
mutant plant and used to individually pollinate the
shoots. One shoot (control) was not pollinated and did
not develop seeds.
Thus, the inbred and hybrid progeny was obtained
from each of the 11 homozygotes for the mutant
allele. The inbred and hybrid seeds were tested for ger-
minating ability and used to obtain one-week-old seed-
The seeds were pickled, rolled in paper, and incu-
bated at 28
C, 100% humidity for a week. Total weight,
root length, and hypocotyl length were estimated for
Phenotype Dependence of the Combining Ability
in Mutant Sugar Beet
A. A. Konovalov
Institute of Cytology and Genetics, Russian Academy of Sciences, Novosibirsk, 630090 Russia;
fax: (3832)33-12-78; e-mail: email@example.com
Received March 3, 2000
—Repetitive gametic selection for a higher frequency of the
semilethal mutant allele of the
alcohol dehydrogenase (ADH) gene yielded viable homozygotes
The plants varied in phenotype from
weak mutant to nearly normal (restored). Phenotypically different plants were individually tested for combining
ability. This parameter was high in plants with the mutant phenotype and tended to decrease, rather than further
increase, in plants with a restored normal phenotype. The results are discussed in terms of viability restoration
mechanisms in homozygotes for semilethal mutant alleles.