Maize Genetics Cooperation Newsletter vol 81 2007
To identify
haploids in the dry-seed stage, the R1-nj marker gene (anthocyanin
coloration of the top of the endosperm and embryo) is widely used. However, there are some inhibitor genes
(C1-I and others) that are able to block the expression of the marker
gene with the result that the selection of kernels with haploid embryos becomes
impossible. These inhibitors are
especially widespread in flint maize.
Thus, there is a need to find an alternative way for the screening of
haploid kernels.
Haploid plants
differ significantly from diploids by their phenotype (Chalyk and Ostrovsky,
1993). Most likely, an embryo with
the haploid number of chromosomes should differ from a diploid embryo by size,
too. An embryo is known to contain
up to 80% of the oil of a whole kernel, and the oil content has a positive
correlation with the embryo size.
Therefore, it was supposed that there might be a difference in oil
content in kernels with diploid and haploid embryos. The purpose of our work was to compare the oil content in
kernels with diploid and haploid embryos.
Eight
genotypes (4 inbred lines and 4 hybrids) were selected for the analysis. First, they were crossed with the MHI
haploid-inducing line (Chalyk, MNL 73, 1999). The selected maternal genotypes had rather good expression
of the R1-nj gene that allowed the kernels with haploid embryos to be
identified easily.
Diploid
hybrids of the maternal genotypes and MHI (with colored embryos), and the
haploid kernels (with colorless embryos) were used for the analysis of oil
content. The sample size for each
variant was 100 kernels. The
analysis was carried out on the Sakslet�s device modified by Rushkovskiy
(1962).
The oil
percentage of the haploids was lower than the diploids in all genotypes. The results of the analysis are shown
in the Table. The averaged excess
of the diploids over the haploids was 19.4%. The coefficient of correlation was 0.76 (significant at the
0.1% level).
Our method of
oil testing required the kernels to be ground up. However, there is a method of biochemical analysis (spectral
analysis) that does not destroy kernels so that they can be used for further
work. Thus, an oil test can be
applied as a marker to identify kernels with haploid embryos. Besides solving the problem connected
with the R1-nj-gene inhibitors, this kind of analysis might be used to
mechanize haploid seed selection.
The first
attempt to identify haploids by oil content was carried out at the Bavarian
State Institute for Agronomy in 2002 (Germany), and the author of this note is
very grateful to Dr. Eder for help.
Table. Oil content in kernels with haploid and
diploid embryos and differences between them.
|
Genotype |
Oil content, % |
Difference, % |
|
|
n |
2n (hybrids with MHI) |
||
|
Inbred
lines |
|
||
|
A464 |
4.00 |
5.23 |
31.0 |
|
A619 |
4.60 |
5.44 |
18.3 |
|
MK01 |
4.16 |
4.75 |
14.2 |
|
Mo17 |
4.01 |
5.04 |
25.7 |
|
Hybrids |
|
||
|
Modavian450 |
4.04 |
4.92 |
21.8 |
|
Porumbeni295 |
4.73 |
5.33 |
12.7 |
|
Porumbeni359 |
3.78 |
4.47 |
18.3 |
|
Mo17xB73 |
3.86 |
4.37 |
13.2 |
|
On
average for all genotypes |
4.14 |
4.94 |
19.4 |
Please Note: Notes submitted to the Maize Genetics Cooperation
Newsletter may be cited only with consent of authors.