Ionara Fatima Conterato

Amphicarpy in Trifolium argentinense: morphological characterisation, seed production, reproductive behaviour and life strategy

Trifolium argentinense Speg. is an amphicarpic species that occurs naturally in native pastures of Rio Grande do Sul, southern Brazil. Amphicarpy is a rare mode of reproduction in which aerial and subterranean seeds are produced by the same individual. In the present paper, we compare morphology, anther number, pollen viability, seed production and mode of reproduction of T. argentinense flowers, and comment on the life strategy of the species. Plants grown from aerial seeds and from the regrowth of storage roots of aerial plants had longer stolons and a larger plant diameter than did those grown from subterranean plants. Plants grown from seeds were also taller than plants grown from storage roots. More resources were allocated to subterranean reproduction in plants of subterranean origin than in those of aerial origin. Aerial flowers produced more seeds, presented more anthers and produced more pollen grains than did the subterranean ones. T. argentinense is a versatile species, self- and cross-pollinated, consistent with the values of high polymorphism information content. T. argentinense adopts the ‘pessimistic strategy’ (early allocation of energy to large subterranean propagules), common in amphicarpic species when growing in disturbed habitats, such as the native pastures of Rio Grande do Sul, where intense grazing and trampling, as well as long seasonal dry spells, may periodically destroy the aerial plants, thus assuring survival by germination of subterranean seeds and regrowth of storage roots.

Morphoagronomic variation in natural populations of Trifolium riograndense (Burkart)

Several species of Trifolium are widely cultivated as forage for animals and green manure. This work aimed to characterize and estimate through morphological and agronomic traits the genetic diversity of natural populations of T. riograndense, an important forage legume from native pastures of the state of Rio Grande do Sul, Brazil. Plant height and diameter, number of primary and secondary stolons, stolon length, number of nodes per primary stolon, internode length, primary stolon diameter, leaf area, petiole length and dry matter production were analyzed in 29 accessions. The first five attributes and dry matter production were evaluated twice. A broad phenotypic variability was observed for almost all characteristics. Positive correlations occurred between petiole length and leaf area (r = 0.68), petiole length and plant height in the first evaluation (0.63), stolon length and plant height (0.58), total dry matter and plant diameter (0.61), and total dry matter and plant height in the second evaluation (0.55). The two most divergent accessions were collected in the same physiographic region and the two less divergent ones in different regions. A dissimilarity dendrogram separated four groups. Accessions collected in a region where T. riograndense is abundant were found to belong to different groups outlining the great variability of this native forage legume. Dry matter production in the first cut was the characteristic that most contributed (20.80%) to accessions divergence followed by number of secondary stolons (12.30%), leaf area (11.07%), and number of nodes per primary stolon (10.93%).

Microsatellite diversity and chromosome number in natural populations of Trifolium riograndense Burkart

Twenty eight natural populations of Trifolium riograndense Burkart, an important forage legume from native pastures of the state of Rio Grande do Sul, Brazil, were evaluated for genetic diversity with eight Simple Sequences Repeats (SSR) markers. Chromosome numbers were also determined. The eight markers were polymorphic, with 35 alleles and an average of 4.37 alleles per locus, and Polymorphism Information Content (PIC) between 0.48 and 0.80. Group analysis based on Jaccard´s similarity coefficient separated the 28 accessions in nine groups, with an average genetic similarity of 0.44, indicating a high genetic variability among the populations. No evident relation between genetic distance and geographical origin was detected. The chromosome number of 2n=2x=16 was found in all populations, indicating lack of intraspecific variability for chromosome number in the species. This information on diversity can be used in conservation strategies as well as in genetic breeding programs of this species.

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.