Maize Genetics
Cooperation Newsletter vol 86 2012
FUNDULEA, ROMANIA
Procera
Genetics
CHISINAU, MOLDOVA
Institute of Genetics and
Physiology of Plants
Aberrant doubled haploid lines in maize
-- Rotarenco V.,
Dicu G.
Doubled haploid (DH) maize lines generally
are created from in vivo induced
haploid plants by artificial chromosome doubling using mitosis inhibiting compounds
such as colchicine (Wan et al., 1989;
Gayen et al.,
1994). DH lines therefore should be homozygous; however, we have observed a
significant phenotypic variation in the progeny of some DH lines.
Possible reasons for this phenomenon
include:
1.
Mutagenesis
a)
Colchicine does not only act as an inhibitor of mitosis but may also
induce mutations. If this happens in the diploid sporophytic
tissue of a treated haploid plant, selfed progenies
will be heterozygous leading to segregation in subsequent generations.
b)
Since the diploidy is the natural ploidy level of maize, the mutation rate of haploids, due
to the influence of environmental conditions, might be higher than that of
diploids.
2.
Paternal gene transfer
Haploid inducers acting as pollinator generally do not
transmit any genes to the resulting haploids, i.e. the induced haploids carry
genes from the maternal genotype only. Yet, occasionally limited male gene
transfer (DNA introgression) was reported in the literature (Fisher, 2004;
Liang Li et al., 2009). This leads to
a transformation of genetic material, no heterozygousity
will occur at the DH level. However, if a male chromosome segment is added to
the female genome leading to aneuploidy, segregation may occur in subsequent selfing generations.
Our studies showed a
significant influence of inducers on the manifestation of quantitative traits
in haploid plants, and that, most likely, was associated with the DNA
introgression (Rotarenco et al, 2009).
Our objective was to reveal the most possible
reason leading to the instability of DH lines.
A well-known inbred line А619 and a DH line, 134, were used in the
study. The 134 line is one of the DH lines derived from our breeding synthetic
population, SP, and after three generations, we noticed a significant
phenotypic variation within this line. In contrast, the inbred line A619 is
characterized as a rather stable genotype. Both lines were crossed with a haploid-inducer line MHI (Chalyk, 1999).
Haploids produced from each line were divided
into two groups. The first group was planted in the field; the second group was
subjected to a chromosome - doubling treatment (Deimling
and Geiger, 1997). There were about 150 haploid kernels in each group. Haploids
planted in the field were randomly pollinated with a bulk of pollen from their
diploid lines, doubled haploids were self-pollinated.
By the pollination of haploids with their
diploid analogues, eight new lines, called reconstituted lines, have been obtained
from each initial line. Six DH lines have been produced from both A619 and 134 lines
by chromosome doubling.
Reconstituted and DH lines have been
compared with the initial genotypes in S2 and S3. Plant height, ear length and coefficients
of variation of these traits were estimated. The experiments were carried out
in three replications on two - row plots.
No significant differences were revealed
between the line A619 and its derivatives, whereas among the
lines produced from the line 134, a significant variability for the estimated
traits was detected. We did not reveal any significant differences between the
S2 and S3 generations. Results of comparing the initial
lines with their DHs in S3 are presented in the table below.
Means of plant
height and ear length, coefficients of variation of these traits in the lines А619 and 134 and their DHs (S3)
|
Initial lines and DH progenies (S3) |
Plant height |
Ear length |
||
|
Mean |
Coef. var. |
Mean |
Coef. var. |
|
|
A619 |
202.2�2.2 |
6.6 |
15.7�0.7 |
20.7 |
|
A619DH1 |
198.2�2.8 |
6.4 |
14.2�0.5 |
13.5 |
|
A619DH2 |
200.5�2.6 |
5.8 |
16.1�0.7 |
17.0 |
|
A619DH3 |
200.3�1.9 |
4.7 |
16.7�0.7 |
15.9 |
|
A619DH4 |
201.8�1.4 |
3.8 |
15.5�0.3 |
8.2 |
|
A619DH5 |
207.1�2.6 |
5.4 |
16.0�0.7 |
17.3 |
|
A619DH6 |
197.4�2.4 |
6.1 |
17.7�0.9 |
13.5 |
|
134 |
269.5�5.6 |
10.6 |
15.1�0.19 |
10.7 |
|
134DH1 |
275.2�2.9 |
4.9 |
16.9�0.21*** |
7.6 |
|
134DH2 |
267.8�2.0 |
3.5 |
14.5�0.16 |
7.6 |
|
134DH3 |
270.2�3.9 |
6.6 |
16.8�0.26*** |
9.1 |
|
134DH4 |
227.3�2.2*** |
5.4 |
15.1�0.13 |
5.8 |
|
134DH5 |
223.4�2.5*** |
6.4 |
14.7�0.16 |
7.1 |
|
134DH6 |
268.0�2.1 |
3.7 |
15.1�0.17 |
7.1 |
*** Significantly (P < 0.001) different from initial line
Lines 134DH4 and
134DH5 were significantly inferior to the initial line, 134, for plant height; 134DH1
and 134DH3 significantly exceeded the initial one for ear length. Four
reconstituted lines, either for plant height or for ear length, differ significantly
from the initial genotype 134 (data is not presented). Additionally, among those 14 lines
derived from the line 134, we have noticed a variation for the beginning of
flowering – up to 10 days.
In all DH lines, the coefficients
of variation have reduced in comparison with the initial genotypes (Table). Thus, most likely, the influence of colchicine is not the main reason leading to the instability of DH lines; the
same can be said about the influence of environmental conditions since we did not
obtain any significant differences among the reconstituted lines derived from the
line A619 (data is not presented).
Differences among the lines
produced from the line 134 may be connected with the fact that the initial genotype
represents a heterogeneous material. At the moment, aneuploidy
is the most preferred version of
the segregation in the progeny of some DH lines.
Every year, we notice a high frequency of
unstable DH lines, named aberrant doubled
haploid lines, among so-called spontaneous doubled haploids - there might
be something in common between these phenomena and we are assuming that that is
aneuploidy.
We are expecting that further
work will bring us more answers on this topic.
ACKNOWLEDGMENTS
We are very grateful to Prof. Geiger (University of Hohenheim) for many valuable suggestions for the improvement
of this note and also for wonderful ideas regarding our studies.
Please Note: Notes submitted to the Maize
Genetics Cooperation Newsletter may be cited only with consent of authors.