| 4. In cyotological examinations of progenies a considerable variation
of chromosome number and a strong tendency to backregulating was observed.
The progenies had a mean-chromosome number that was on an average one chromosome
smaller than the chromosome number of the mother plant. This tendency of
backregulating seems probably to be caused by irregular meiosis and variable
fitness of the different haploid gametes. 5. Studies on fertility and plant height of progenies indicated further that not only fertility and plant height of single plants but also mean fertility and mean plant height of the offspring is correlated to the chromosome number. The relations were the same as in studies on single plants. There was only a shifting in relation to the maximal values. The offspring of plants with 57 chromosomes had better fertility and plant height than the offspring of euploid plants. This shifting was expected because dependent upon the tendency of backregulating plants with 57 chromesomes produced the most euploid offspring. 6. It was further observed that the offspring of mother plants with quite the same chromosome number partly differed significantly in mean values for fertility and plant height. It is possible that these differences are caused by genotypical differences between the mother plants. A reliable evidence could not be established because the progenies were only small and other reasons had to be taken into consideration too. 7. The aneuploid composition of the offspring was also found to be influenced by environmental conditions. Progenies of aneuploids with different chromosome number had different survival rates and especially in progenies of aneuploids with low chromosome numbers (50 resp. 49 chromosomes) a great deal of plants died before reaching maturity. 8. In relation to aneuploid composition of later generations of "Trc 220" the present studies indicate that 3 points are of decisive importance : 1. Tendency to backregulating, 2. Differences in fertility and fitness of aneuploids with different chromosome number and 3. Selection environment and elimination of plants with low fitness. |
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