Marioara Urda _Grebenisan_ rezumat_teza_engleza - USAMV Cluj ...

More documents

Recommendations

Info

<strong>Marioara</strong> 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 high number of aborted ovules in the tetraploid genotypes can be explained by several causes, among which ovary sterility, determined by anomalies of the embryonic sac, represents a limitative factor for the seed production capacity in plants. Another cause of low fertility is represented by the high number of unfertilized ovules, respectively the low number of ovules with formed embryos (table 5.13 and 5.14). Although the study of embryogenesis does not intend to fully explain the causes of the lower fertility of the tetraploid red clover genotypes, it still points out some genetic aspects with causal effects upon unsatisfactory seed yields. Analyzing the various factors that can reduce fertility in autotetraploid red clover , we were interested in cytological and genetic causes triggering multivalent chromosomes, gametes and aneuploidy plants, ovaries and embryo abortion, overcoming a number of alleles/locus caused by abnormal meiosis in tetraploid forms, low pollen fertility etc. It should be noted that the families of tetraploid red clover used in our studies are differentiated in terms of average fertility. From here we can draw the conclusion that there occurs a “family effect”, which should be taken into account in establishing relationships between meiosis and fertility abnormalities. The studies have revealed three types of abnormalities, with a relatively high frequency, namely: the presence of monovalent, divalent and tetravalent, the irregular presence of anaphase I, the presence of supernumerary microspores. It was shown that the irregular distribution of anaphase leads to the finding that approximately 50% of infertility is due to this cause. It was noted that unviable pollen grains are the result of meiotic abnormalities, without being able to explain that this phenomenon singularly influences the low fertility of polyploids. If abnormalities occur in the case of macrosporogenesis, they are undoubtedly the cause of a decrease in fertility due to the abortion of non-equivalent embryos (table 6.4, table 6.5). 12
<strong>Marioara</strong> 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 presence of triploid plants can also contribute to the diminishing of the general fertility of a tetraploid population. It may be suggested that the chromosomal abnormalities which lead to the formation of embryos of viable or aborting aneuploids are responsible for part of the impairment of fertility and viability of autotetraploid populations and that the viability of triploid embryos has adverse consequences upon yield (table 6.8). One of the causes that may interfere with the formation of tetraploid red clover seed may be due to causes independent of the genetic base, being caused by the disturbing influence of the haploid pollen and the influence of environmental conditions. The presence of haploid and diploid pollen can cause anomalies in the seed production process. Countering this situation is facilitated by implementing appropriate isolation distances between di-and tetraploid seed lots or by providing a “washing strip” between them. A particularly disturbing effect was found when tetraploid seed plants were pollinated with haploid pollen from the diploid genotypes. The obvious disturbing influence on the average number of seeds in tetraploid genotypes flower heads occurred in the immediately adjacent rows of diploid red clover, the effect being visible on a 7 m distance from the haploid pollen source (table 7.4). The negative influence of the diploid pollen on the number of seeds in seed heads, in diploid forms, is insignificant and not statistically assured. In the case of intercalation of an insulation strip (sainfoin) between red clover seed lots with different degree of ploidy, there is an increase in the number of of seeds / flower head in tetraploid forms, as a result of “washing out” the insects on the isolation strip (table 7.6 ). The decrease in productive capacity of the tetraploid red clover when placed near the diploid onecan be explained by the fact that haploid pollen tubes, as 13
Page 1 and 2: UNIVERSITY OF AGRICULTURAL SCIENCES
Page 3 and 4: Marioara GREBENIŞAN Summary of the
Page 11: Marioara GREBENIŞAN Summary of the

Marioara Urda _Grebenisan_ rezumat_teza_engleza - USAMV Cluj ...

Create successful ePaper yourself

Delete template?

Save as template?