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Results and discussion
Fertility segregation and utilization of the male sterile gene of
Ms2 in triticale
The dominant male sterile Ms2 gene has been located on the
short arm of 4D chromosome by Liu and Deng (1982). We have made
several crosses and backcrosses between the male sterile triticale
Ms2 and hexaploid and octoploid triticale in order to study and
utilize its expression in triticale. The values of chi2 in
Table 1 indicate that the ratio between the
sterile plants and the fertile plants of octoploid (AABBDDRR) Fl is
0.96: 1; the ratio between the sterile plants and the fertile plants
of (AABBRRD) Fl of octoploid and hexaploid triticale is 0.91: 1 which
all conform to the predicted ratio 1: 1. However, the number of
sterile plants significantly decreased according to the increase of
backcross number. The ratios were 0.47: 1; 0.45: 1; 0.29: 1 and 0.16:
1 respectively. These ratios are identical with the elimination ratio
of 20-50% of D genome chromosome as studied by H. Kihara (Nishiyama
1954). The above results indicate that the dominant male sterile
Ms2 gene expressed steadily. The stamens of the sterile plants
is abortive, which induces self sterility. The glume opened normally
and was able to produce seed after open or artificial pollination, so
it is useful to gene recombination. The stamens and pistil of fertile
plants develop normally and they are useful to self-fertilize.
Therefore, the dominant male sterile triticale is a very useful cross
tool for gene recombination and rotational selection.
Transfer of Ms2 male sterile lines
The sterile plants not only play a role in recombination of genes in
rotational selection, but also provide half of the genetic factors of
hybrids. Nearly all the lines belong to 4-5 grades, because of their
narrow genetic base and poor traits, especially poor plumpness.
Therefore, we used AH602 AH685, AH999, AH1005 and 20 triticale lines
with different traits in transfer breeding before mass crossing to
improve the plumpness and other traits of the primary sterile lines.
The plumpness had decreased 0.85 class, from 4.52 + or - 0.36 in 1983
to 3.67 + or - 0.54 in 1986 (Table 2),
through improvement, and the plumpness of all triticale sterile lines
had increased nearly one grade. Some combinations even reached 3.2
grade. Thus they have created good base for rotational selection.
Preliminary results of rotational selection
First, the distribution level of plumpness has increased. It can be
seen from the comparison of the mean plumpness of fertile plants in
Table 3. C0-C1=0.24, C0-C2=0.72, C-C3=0.80,
C1-C2=0.48, C1-C3=0.56, C2- C3=0.08. The number of fertile plants in
C1 population averaged 3.43 and it has not exceeded the mean value
3.26 of parents. However, the number of fertile plants in C2
population averaged 2.95 which exceeds the mean value 3.09 of their
parents. The plumpness of sterile plants in each rotation (year) has
increased by 0.23 which is twice the average conventional lines. In
addition, the plumpness proportion of each grade in a population has
changed. e.g. the percentage of seeds belonging to 4-5 grades in
populations of sterile lines or fertile lines has decreased from 40%
to 1%, but the percentage of seeds belonging to grade 3 or above has
increased significantly, especially in the population of C2 fertile
lines, the percentage of seeds of grade 2 and grade 2.5 has increased
from 1% to 15 %. In C3 population the percentage has increased to 20%
or more. These results indicate that through rotational selection
genes favorable to seed plumpness have increased, thus laying a sound
foundation for synthesizing other good traits.
Conclusion
Seed plumpness is a difficult problem in triticale breeding. We have
done several thousand of cross combinations and long term pedigree
selections, but without good results. Transfer of the dominant male
sterile Ms2 gene into octoploid triticale for rotational
selection has been made in an attempt to break down the adverse gene
linkage with plumpness and to accumulate the favorable quantitative
character genes through extensive gene recombination. We attempted to
combine good traits such as early maturity, dwarfness, disease
resistance and high yield potential on the basis of higher seed
plumpness. Rotational selection for seed plumpness improvement is
better than pedigree selection and this is related to the basic
materials of sterile plants and group combination of recurrent
parents. After this work, the mean value of the population was equal
to or exceeded that of their parents and showed that it is an
effective way for improving seed plumpness of triticale. Further
studies are needed in the future because rotational selection has
just entered the third rotation.
In the cross and backcross between male sterile octoploid triticale
and hexaploid triticale, the proportion of sterile plants was
decreased gradually with the increasing number of backcrosses, and
this is related to the loss of the D genome chromosome. However, in
some combinations there is still a ratio of 1: 1 between sterile
plants and fertile plants. It means that 4D chromosome has not been
lost or that substitutions and translocations of chromosomes may have
occurred. Therefore, the sterile line of hexaploid triticale should
be used in rotational selection. It is possible to select new sterile
lines of hexaploid triticale from our work, thus a new field will be
opened for the cross breeding of hexaploid and octoploid triticales
and studies on chromosome engineering of triticale.
References
Liu BH and Deng JY (1982) Genome study and telosomic analysis of
the single dominant male-sterile Ta1 gene in common wheat.
Scientia Sinica 29: 516-525.
Liu BH and Deng JY (1986) A dominant gene for male sterility in
wheat. Plant Breeding 97: 204-209.
Ji FG and Deng JY (1986) Utilization of the dominant male sterile
Ta1 gene in triticale breeding programme. 1st Int Triticale
Symp, Sydney 77-80.
Darvey NL (1986) Dominant male sterility in hybrid wheat and
triticale production. 1st Int Triticale Symp., Sydney 82-85.
Wang CY and Sun YS (1986) Triticale breeding in China, 1st Int
Triticale Symp, Sydney 50-58.
Nishiyama I (1954) Cytogenetics in Triticum and its related
gene. In: Studies on wheat plants, Ed: Kihara H. Yokendo:
461-471.
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