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Both the grain weight and the spike number contributed to the
increased plant yield. The development of the extremely variable
traits listed above depended on the efficiency of the plant
metabolism. The less variable traits (the grain and spikelet numbers
in a spike, the stem and upper internode lengths) depended rather on
the rates of morphogenesis (Kuperman et al. 1982). Thus, the increase
of the values in both these groups of traits can be achieved by the
increase in the functioning efficiency of their physiological
systems. The differences between the sibs that are progenies of the
same monosomic plant suggest the heterogeneity of this plant.
However, the entire series was bred basing on only one genotype of
the recurrent parent. Consequently, the heterogeneity in certain
monosomic lines appeared later in the process of reproduction under
monosomic state maintenance, which may have contributed to the
formation of CCG. Thus, there are grounds to suggest that longterm
maintenance of the aneuploid state in certain cases can lead to
increased yield. In other cases, the compensatory aneuploid state of
the relevant alleles can disturb the genetic balance of the plant. In
the latter situation, a decrease in the yield can be observed. In the
similar experiment, Arbuzova and Maystrenko (1981) did not reveal any
significant differences among the disomic families in the pedigrees
of cv. Saratovskaya 29 monosomics (Maystrenko 1971). The monosomics
used in this experiment were derived by selfing BC9 plants
from final crosses in the development of these monosomic lines. Any
backcrosses in the course of monosomic line development disrupted the
CCG by introducing the genome of the recurrent parent. In this
experiment, only one selfing was performed after the last back-cross,
but several generations of selfing are necessary to reveal the
working compensatory alleles. In our experiment, 15 generations of
selfing passed after the final crosses in the development of Milturum
553 monosomic line before we started to isolate the disomic families.
We can suppose that, during all these 15 generations, the breeders
unconsciously chose for further propagation the monosomics with
higher yield parameters.
In other experiment carried out in 1998, we used several disomic
progenies of the same monosomics of cultivars Saratovskaya 29 and
Diamant (bred by Dr. O.I. Maystrenko) after over fifteen generations
in monosomic state. Their comparison with the recurrent parents
demonstrated significant differences in several quantitative traits
(Table 3). However, unlike Milturum 553
disomics, the mean value deviations were mainly directed towards the
decrease in grain production.
The CCG effects observed depend on the genome of the recurrent
parent: differences between sibs from monosomic lines Saratovskaya 29
and Diamant occur rarer than in Milturum 553 monosomic progenies and
the character of changes observed is different. The results obtained
are not unambiguou, however, the authors tend to believe that such
phenomenon may be found also in other monosomic series. Thus, both
the maintenance under conditions of compulsory monosomic status
during a large number of generations and unconscious selection for
high yield parameters provided by breeders resulted in the formation
of the compensation system in the sets of monosomic lines that
enhanced significantly the plant metabolism. The increased values of
most of the parameters recorded in the disomic families compared with
the recurrent parent can be explained by this enhanced metabolism.
The differences among sib disomic families from the same monosomic
plant evidence heterogneity as one of the constituents of CCG and the
variability of possible combinations of the genes involved in this
complex. Our results provide additional arguments to suggestion
(Goncharov 1992) that the results obtained with monosomic lines in
investigation of quantitative traits should be considered carefully.
In this paper, the compensation effects were almost not revealed
earlier than in the tenth generation of selfing. Only some of the
lines studied demonstrated these effects. Not all the lines that
depress the growth and productivity cause the formation of the CCG.
We attempted to obtain the CCG in near- isogenic lines of cv.
Novosibirskaya 67 carrying dwarfing genes. Selection for the
increased height and yield was carried out in ANK-11 (Rht3)
and ANK-12A (Rht1 and Rht2 ) starting from
BC9S9 and lasted without any results for six
generations. Our data suggest that formation of the CCG may
constitute a problem for stable maintenance of lines in genetic
collections, especially if the line is deficient for chromosome
number or carries a semilethal allele. The CCG formation can be also
caused by other factors decreasing viability, for example, an alien
cytoplasm or inbred depression in cross-pollinating species. An
unconscious selection for more productive individuals cannot be
excluded while maintaining genetic collections. Thus, we can expect
the formation of the CCG changing a number of characters.
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