Marioara Urda _Grebenisan_ rezumat_teza_engleza - USAMV Cluj ...
Marioara Urda _Grebenisan_ rezumat_teza_engleza - USAMV Cluj ... Marioara Urda _Grebenisan_ rezumat_teza_engleza - USAMV Cluj ...
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 determination of blooming flower heads has revealed a wide range of oscillation according to genotype, as the diploid forms are superior to the tetraploid ones, and also in relation with the ecological culture area (table 3.1). As regards the intrinsic aspects of seed production, it has been proved that there are significant differences between the number of flower heads/individual plant and the number of flower heads/surface unit (table 3.2). The diploid forms appear to be superior to the tetraploid ones, if we consider the number of flower heads/sq m, which has a negative impact upon the yield of the tetraploid seed plants. The number of flowers/flower head is a determinant element for plant sexuality in clover, being considered a quite precise indicator of potential fertility. The highest values occur at maximum flowering time; generally speaking, diploid forms provide a higher number of flowers per flower head, as compared to tetraploid genotypes (table 3.3). Another observation is that, by delaying the first cut, there occurs a decreasing tendency in what regards the number of seeds/flower head, in direct correlation with the ecological culture area (table 3.5). The weight-of-thousand-kernels indicator displays the most reduced oscillation. Apparently there is a certain influence of the first cut timing upon this trait. The differences that occur are in favour of the tetraploid genotypes (1.6-1.7 g for 2n and 2.2-2.4g for 4n) and are not an advantage in the process of initiating tetraploid red clover cultures. As far as the determination of the production capacity of the seed plants is concerned, the calculations of the biological yield based on average values of the individual production factors outline significant differences between the calculated yield and the real yield, the one obtained in the field. These differences are conditioned by the ecological culture area, climatic conditions and genetic differences of the biological material. Major influence comes from the lack of uniformity in what regards the flowering and seed ripening, precarious pollination, 8
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 field work, harvesting periods, as well as the inherent loss occurring in the field, all these leading to the already mentioned differences (table 3.11). One of the key-ways that can lead to the reducing of the seed yield loss lies in directing the seed plant flowering process, which has to last for a short time, with a flowering climax, thus ensuring the uniform ripening of the seed plants. It was noticed that the poliploidization process of the red clover produces certain morphological modifications in the plant, which cause a diminishing of the productive capacity of the seed plants of the 4n type rather that of those of the 2n type. These modifications are enhanced by soil conditions and climatic factors, which can influence, in a positive or negative way, upon the productivity differences of the two forms of red clover with different ploidy levels. The existence of genetic variability that can be used, for certain categories of seed production, with tetraploid genotypes of red clover draws us to the conclusion that the fructification potential of tetraploid red clover can be improved by selection. However, the full exploitation of this potential requires substantial improvement of the pollination conditions. The determinations referring to the pollinating entomofauna and the pollination frequency show the fact that the main pollinators of the red clover are honey bees and bumble bees species (table 4.3). There is also an interrelation between the biotic and abiotic factors and the efficiency of the pollination done by apoides in the case of red clover seed plants. An analysis of the total number of bees and bumble bees that visit the red clover fields highlights the fact that, as compared to the total number of apoides, only 49.2-88.6% visits the tetraploid red clover, which has a negative influence upon the percentage of formed seeds in this genotype (table 4.4). As for the daily frequency during maximum flowering time, the number of apoides that visit the tetraploid red clover represents 57.1-81.5% of the total number of the ones that visit the diploid red clover. 9
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<strong>Marioara</strong> GREBENIŞAN Summary of the PhD thesis<br />
Research on the structure of di- and tetraploid red clover seed plants and the influence of meiotic<br />
anomalies on the fertility of autotetraploid forms<br />
field work, harvesting periods, as well as the inherent loss occurring in the field, all<br />
these leading to the already mentioned differences (table 3.11).<br />
One of the key-ways that can lead to the reducing of the seed yield loss lies<br />
in directing the seed plant flowering process, which has to last for a short time, with<br />
a flowering climax, thus ensuring the uniform ripening of the seed plants.<br />
It was noticed that the poliploidization process of the red clover produces<br />
certain morphological modifications in the plant, which cause a diminishing of the<br />
productive capacity of the seed plants of the 4n type rather that of those of the 2n<br />
type.<br />
These modifications are enhanced by soil conditions and climatic factors,<br />
which can influence, in a positive or negative way, upon the productivity<br />
differences of the two forms of red clover with different ploidy levels.<br />
The existence of genetic variability that can be used, for certain categories of<br />
seed production, with tetraploid genotypes of red clover draws us to the conclusion<br />
that the fructification potential of tetraploid red clover can be improved by<br />
selection. However, the full exploitation of this potential requires substantial<br />
improvement of the pollination conditions.<br />
The determinations referring to the pollinating entomofauna and the<br />
pollination frequency show the fact that the main pollinators of the red clover are<br />
honey bees and bumble bees species (table 4.3).<br />
There is also an interrelation between the biotic and abiotic factors and the<br />
efficiency of the pollination done by apoides in the case of red clover seed plants.<br />
An analysis of the total number of bees and bumble bees that visit the red<br />
clover fields highlights the fact that, as compared to the total number of apoides,<br />
only 49.2-88.6% visits the tetraploid red clover, which has a negative influence<br />
upon the percentage of formed seeds in this genotype (table 4.4).<br />
As for the daily frequency during maximum flowering time, the number of<br />
apoides that visit the tetraploid red clover represents 57.1-81.5% of the total number<br />
of the ones that visit the diploid red clover.<br />
9
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