ISSN 10227954, Russian Journal of Genetics, 2010, Vol. 46, No. 6, pp. 758–764. © Pleiades Publishing, Inc., 2010.
Original Russian Text © M.E. Mikhailov, 2010, published in Genetika, 2010, Vol. 46, No. 6, pp. 853–860.
In the last years, significant progress has been
achieved in the technique of producing plant dihap
loid lines. Generation of dihaploid lines of maize, bar
ley, wheat, rice and other cultures has been developed.
Tens and even hundreds of lines were reported to
appear within a season [1–3].
The interest to dihaploid lines is understandable
their use provides new possibilities for combining
genetic material. Producing of a dihaploid line is gen
eration of a diploid from a diploid through the haploid
stage. A gamete of a diploid plant gives rise to the hap
loid, whose genome is then duplicated, producing a
genetically homologous dihaploid line after reproduc
tion. Its genome is identical to the duplicated genome
of one of the gametes of the progenitor diploid plant.
The result of this operation is equal to the result of
longterm inbreeding. A set of dihaploid lines derived
from a hybrid plant genetically resembles
heterozygotes. However, such set favorably differs
by (1) the absence of the masking effect of het
erozygotes; (2) gametic segregation 1 : 1, which signif
icantly increases the frequency of various polygenic
combinations; and (3) the absence of the environmen
tal bias in the expression of quantitative traits, since
each genotype in this case is represented by a total line
rather than by an individual by plant.
Dihaploid lines are widely used in breeding for
combination of genetic material to provide mass pro
duction of new lines. Sometimes such lines were char
acterized by complete or partial fixation of heterosis
even in the first cycle of selection . However, this
does not occur in all cases and is theoretically possible
only for oligogenic heterosis. Haploid stages are also
used in the process of saturating backcrossing [4, 5].
Various schemes of haploid stages inclusion in the pro
cedure of recurrent breeding have been designed and
used for more precise selection and rapid homozygo
tization of the selected variants [2, 6, 7].
These approaches of the dihaploid lines use are
modifications of previously used breeding schemes.
Selection of variants in a heterogeneous population
followed by inbreeding was also used previously. Sub
stitution of inbreeding by dihaploidy results in
decreasing the breeding time, but does not change
anything genetically. The inclusion of dihaploid stages
in the schemes of saturating backcrossing and recur
rent breeding increases their efficiency, but, these
schemes do work without dihaploids.
However, new possibilities of genetic material
combination producing dihaploid lines allow to use
nontraditional breeding schemes designed specially
for dihaploids. In the present study, we propose such a
scheme named enriching–restoring and intended for
complete or partial accumulation of favorable alleles
responsible for heterosis in the homozygous line.
The aim of the scheme is to collect in a homozy
gous genotype the largest possible number of favorable
alleles from two lines demonstrating heterosis of any
nature except overdominance. The parental lines are
assumed to be totally homozygous. Thus, each locus
differing between the lines, is represented by two alle
les, one of which, increasing the value of the selected
trait, is called plus allele, value, while the other one,
decreasing this trait, minus allele. The case when both
alleles are identical was not examined, as it means
either overdominance (both alleles are equally impor
tant for heterosis) or noninvolvement of this locus in
the heterosis effect (both alleles are equally nonimpor
tant). Let us assume that both alleles have equal prob
ability to be transferred into the haploid and then in
the dihaploid line (DH line) . The distribution of
plus alleles between the parents is assumed to be
A New Possibility of Dihaploid Lines Use:
Enriching–Restoring Breeding Scheme
M. E. Mikhailov
Institute of Genetics and Physiology of Plants, Academy of Sciences of Moldova, Kishinev MD 2002;
Received July 8, 2009
—Enriching–restoring breeding design based on dihaploid lines usage for the complete or partial
collection of favorable alleles responsible for heterosis in a homozygous line is proposed. The efficiency of the
scheme was checked via the mathematical model considering complicating factors.
MATHEMATICAL MODELS AND METHODS