Maize Genetics Cooperation Newsletter vol 84 2010
Please Note: Notes submitted to the Maize Genetics
Cooperation Newsletter may be cited only with consent of authors.
SARATOV, RUSSIA
Saratov State University
Two
technologies of maize breeding on the basis of parthenogenesis
Tyrnov, VS
As it has been shown in our research, there
exist two different mechanisms of haploids origination. The first is connected
with specific features of male gametophyte and it leads to a unitary
fertilization. On this basis we created haploinducing
lines, which usage as pollen parents leads to haploids originating with
frequencies up to 10 % and above. The second mechanism is associated with parthenogenesis,
controlling by nuclear factor of maternal plant. It was proved by the method of
genetic marking and by cytoembryological analysis.
The part of the data was published (Tyrnov, 1983, 1994,
1997, 2000, 2002, 2007). The frequency of parthenogenesis, as a rule, reached
of some dozens of percents, up to 100. We considered it as a good precondition
for further work on synthesis of unreduced obligate and facultative apomixes.
However, the possibilities of heritable reduced parthenogenesis use for production
of both haploids and derivate diploid homozygous lines did not seem to us
enough perspective ones. It was connected with that a great number of haploids
would be produced in field by heritable reduced parthenogenesis,
that should limit possibilities of their commercial use. It was not
clear, if it is possible to produce effectively and quickly the new parthenogenetic lines – analogies, necessary for new
hybrids production. Later it has been ascertained:
1) an
ability to parthenogenesis can be transferred to progeny by egg and pollen;
2) the
signs and conditions have been discovered, which allow to make effective
selection on parthenogenesis and produce of new lines;
3) the simple and reliable genetic
system has been worked out, which give an opportunity to produce with high
frequency (dozens of percents) matroclinic haploids
on the first stage, i.e. by homozygous lines development; by this about 3-10% matroclinic diploids produce additively, which in
accordance to some data are spontaneously diploidizated
haploids;
4) system
has been worked out accordance to which haploids in the commercial hybrids
progeny are produced in field with a frequency about 0,3-1,0%. It is some what higher than an average frequency for maize –
0,1%. However, it does not influence appreciably on a common yield. At the same
time the origin of some number of haploids in field can be of the positive
importance. Haploids can be in future the initial material for selection since
by descending from hybrids and undergoing of hard selection in the field conditions
they can be the bearers of the new valuable genetic combinations. Besides, by
of using a number of methodical modes, it can be possible to produce haploids
with the high frequency in commercial hybrids as well.
Thus, our technology allows
regulating of parthenogenesis frequency from insignificant to very high values.
There is one more advantage,
working for a perspective. Apomixis, with the help of
which fixation of heterosis and other unique traits
in the hybrid progeny is supposed to realize, is more probably multicomponent phenomenon, including apomeiosis,
normal development of endosperm by untypical conditions (different ploidy, genomic imprinting) and parthenogenesis.
Parthenogenesis presence in a great number of cultivated hybrids facilitates
significantly the decision of the other parts of the problem that we have
demonstrated in the model experiments.