Marioara Urda _Grebenisan_ rezumat_teza_engleza - USAMV Cluj ...

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Marioara GREBENIŞAN Summary of the PhD thesis Research on the structure of di- and tetraploid red clover seed plants and the influence of meiotic anomalies on the fertility of autotetraploid forms The abiotic factors, which also include the weather conditions, can have a direct or indirect influence on red clover pollination, by consistently affecting both the flowering dynamics and the flight of the pollinators. The comparative data collected in Cluj-Napoca show the fact that the morphological modifications determined by the increase of the ploidy level affect the pollination and seed formation processes, in favour of the diploid red clover genotypes, which explains, to a certain extent, the difference in productivity potential between the seed plants belonging to different ploidy groups (table 4.9). There has been noticed an influence, either positive or negative, of the weather factors upon the interrelationships red clover-pollinators. The good understanding of the correlations between these two factors can allow for the determination of the most favourable exploitation period for red clover seed plants. By studying the evolution of embryogenesis it was possible to highlight the action of multiple factors that contribute to the diminishing of the red clover fertility. The phases that the pollen grain goes through as part of the pollination and fertilization process must give an answer to the question if its participation in this process can produce any beneficial effects upon the seed yield in the case of red clover. The tests regarding germination, elongation, pollen viability indicators, as well as the growth of pollen tubes in compatible and non-compatible pistils have pointed out major differentiations between red clover genotypes with different ploidy level. The ploidy level correlates with pollen viability; as the percentage of abnormal and unviable pollen is higher in tetraploids, the fertility of these genotypes is lower (table 5.1). The in vitro germination of pollen takes place in the first two hours after the pollination, and the elongation of the pollen tubes is faster in the first 12 hours, whereas in the next 12 hours the growth rate is very low. 10
Marioara GREBENIŞAN Summary of the PhD thesis Research on the structure of di- and tetraploid red clover seed plants and the influence of meiotic anomalies on the fertility of autotetraploid forms The duration of the pollen tubes growth is similar for the 2n and 4n forms, the differences occurring in the growth speed and the length to the ovary. germination. A population effect was noticed, with positive influence upon pollen The repetition of compatible and incompatible pollination weakens the mechanisms of self-incompatibility of the red clover, mainly of the tetraploid forms. An interesting aspect of the comparison regarding the fertility of red clover with different ploidy levels is represented by the evolution of embryogenesis. The research undertaken for the interval pollination-seed formation has shown the development of ovaries and embryos under the conditions of free pollination (PIL), spontaneous pollination (APS) and artificial self-pollination (APA). The study of embryogenesis from the point of view of the development of the pre-embryo, suspensor, cotyledons and apex highlighted the fact that, in the case of free pollination (PIL), the difference between di- and tetraploids consists mainly in the more obvious earliness of the tetraploids in the first 10 days after pollination, whereas both ploidy forms reach the maximum development of embryos in 14-15 days after pollination (table 5.7). Self-pollination does not bring any morphological changes during embryogenesis. However, a higher percentage of normal ovaries and ovules was noticed in diploid forms. Another observation was that the tetraploids provided a higher percentage of aborted embryonic sacs than the diploids, whereas after pollination, the fertility decrease percentage is similar in di- and tetraploids. It appears that poliploidization affects fertility more in macrosporogenesis, as compared to the same phenomenon in diploids. The fertility decrease seems to happen owing to the abortion of one of the ovules present in a normal ovary, the abortion of the second one or of the embryo being also possible (table 5.9). 11
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