Nair Dahmer

Cytogenetic data for Paspalum notatum Flügge accessions

Several species of the genus Paspalum L. are important forages, due to quality, productivity and tolerance to environmental stresses. Chromosome numbers, meiotic configurations and pollen fertility were evaluated in a collection of 85 accessions of Paspalum notatum Flugge and in seven accessions of Pensacola (P. notatum var saurae). All P. notatum accessions were tetraploid, with 2n = 4x = 40, except one diploid accession, considered as an escape of Pensacola. All Pensacola plants had 2n = 2x = 20. Meiotic configurations at diakinesis and metaphase I varied among tetraploid accessions, from plants with only bivalents to plants with high frequency of quadrivalents. Pollen fertility varied from 82.5 to 95.9% among diploid accessions and from 72.4 to 97.9% among the tetraploid. Due to the apomictic mode of reproduction of tetraploid P. notatum, meiotic irregularities can be maintained by the plants without harming their propagation. At the same time, pollen fertility should be high enough to assure endosperm development, since the species is pseudogamous. Wild diploid P. notatum populations, apart from the endemic P. notatum var saurae are very rare. From a plant breeding point of view, all the examined tetraploid accessions are potentially male-fertile and could be used as males in crosses.

Genetic diversity assessed by microsatellite markers in the amphicarpic species Trifolium polymorphum Poir.

Trifolium polymorphum Poir. is an amphicarpic forage legume from southern Brazil, Uruguay, Argentina, Paraguay and Chile. Information on the genetic diversity of natural populations in natural grasslands in southern Brazil is limited. In order to increase the knowledge about this species, an analysis of the genetic diversity was carried out in 10 natural populations of T. polymorphum with the use of 20 microsatellite markers. The expected heterozygosity in T. polymorphum populations ranged from 0.40 to 0.43, with a mean of 0.42. A total of 193 alleles were detected with a mean of 9.3 alleles per locus and polymorphic information content (PIC) for these markers of 0.62 to 0.89 with a mean of 0.84.The grouping based on the Jaccards coefficient of similarity classified populations, regardless of their regions of origin, into two groups with a mean similarity coefficient of 0.32, reflecting the high genetic variability of the populations, especially those located in the Campanha phytogeographic region. This information on diversity can be used to plan future germplasm collection strategies for conservation purposes and also for the breeding of the species.

Occurrence and significance of polysomaty in species of Mimosa L.

Polysomaty is the occurrence of cells with different ploidy levels in the same organ or tissue and there are records of this in root-tip cells of some Mimosa species. The objective of the present work was to verify the occurrence, possible cause and significance of polysomaty in a range of species of this genus. In root-tip cells of 68 accessions of 43 diploid and tetraploid Mimosa species, the percentage of polysomatic cells ranged from 5% to 87%. Pretreatment with the antimitotic paradichlorobenzene did not cause polysomaty but increased it in some accessions. When relating seedling root size and percentage of polysomatic cells, for most of the species a higher percentage of polysomatic cells was found in roots from 6 to 10 cm length. For M. scabrella (“bracatinga”), a comparative analysis of seedling root-tip cells and root-tip cells from well-developed plants kept in pots in a greenhouse showed that polysomaty occurred only in the seedling root-tips. The data suggest that, in Mimosa, polysomaty occurs only for a short period of the seedling development, probably as a natural mechanism to accelerate its development and establishment.