C. T. Karia

Variabilidade genética e ecológica de Stylosanthes macrocephala determinadas por RAPD e SIG

Stylosanthes macrocephala M. B. Ferr et S. Costa is a leguminous species used as forage, cover crop and as a pioneer plant to recover degraded areas. Inexistence of stable morphological descriptors and lack of ecogeographic information about collecting sites bring difficulties to the studies of this species. The objective of this work was to use the geographic information system (GIS) and RAPD markers to obtain ecological and molecular descriptors and to study the genetic variability of 87 S. macrocephala accessions. The accessions were collected from different ecogeographical areas in seven Brazilian States, five hydrographic regions, seven vegetation types and seven soil types. Collecting sites ranged from 1 to 1,298 m above sea level with annual rainfall from 550 to 2,870 mm. Accession distribution along those diverse ecosystems indicate high adaptive diversity. Using 161 RAPD markers, genetic distances between accessions ranged from 0.02 to 0.42. These genetic distances allowed the establishment of ten genetic groups. Accessions collected in specific hydrographic region tended to be grouped in the same genetic group. Accessions collected in Bahia and Minas Gerais States showed high genetic variability. The high genetic variability observed in the accessions showed the importance of this S. macrocephala collection for breeding programs.Stylosanthes macrocephala M. B. Ferr et S. Costa is a leguminous species used as forage, cover crop and as a pioneer plant to recover degraded areas. Inexistence of stable morphological descriptors and lack of ecogeographic information about collecting sites bring difficulties to the studies of this species. The objective of this work was to use the geographic information system (GIS) and RAPD markers to obtain ecological and molecular descriptors and to study the genetic variability of 87 S. macrocephala accessions. The accessions were collected from different ecogeographical areas in seven Brazilian States, five hydrographic regions, seven vegetation types and seven soil types. Collecting sites ranged from 1 to 1,298 m above sea level with annual rainfall from 550 to 2,870 mm. Accession distribution along those diverse ecosystems indicate high adaptive diversity. Using 161 RAPD markers, genetic distances between accessions ranged from 0.02 to 0.42. These genetic distances allowed the establishment of ten genetic groups. Accessions collected in specific hydrographic region tended to be grouped in the same genetic group. Accessions collected in Bahia and Minas Gerais States showed high genetic variability. The high genetic variability observed in the accessions showed the importance of this S. macrocephala collection for breeding programs.

Isolation and characterization of microsatellite loci in the tropical forage legume Stylosanthes guianensis (Aubl.) Sw.

Stylosanthes guianensis is an important tropical pasture legume. Knowledge of genetic diversity and structure of S. guianensis populations is of great importance for the conservation and germplasm management of this species. Thus, 20 microsatellite markers were developed from a S. guianensis enriched library. The microsatellites were characterized in 20 accessions from the germplasm collection of the Empresa Brasileira de Pesquisa Agropecuária (Embrapa). The average number of alleles per locus varied from 2 to 7, with an average of 4 alleles per locus. The observed and expected heterozygosities ranged from 0 to 0.60 and 0.10 to 0.85, respectively. This new set of microsatellites will contribute towards studies of genetic diversity and conservation of S. guianensis.

Identification of Stylosanthes guianensis varieties using molecular genetic analysis

Molecular genetic diversity and population structure analysis were used to clarify the controversial botanical classification of Stylosanthes guianensis. The accessions were clustered in nine groups, each of which was mainly composed of only one of the four botanical varieties.

Using genetic diversity information to establish core collections of Stylosanthes capitata and Stylosanthes macrocephala.

Stylosanthes species are important forage legumes in tropical and subtropical areas. S. macrocephala and S. capitata germplasm collections that consist of 134 and 192 accessions, respectively, are maintained at the Brazilian Agricultural Research Corporation Cerrados (Embrapa-Cerrados). Polymorphic microsatellite markers were used to assess genetic diversity and population structure with the aim to assemble a core collection. The mean values of HO and HE for S. macrocephala were 0.08 and 0.36, respectively, whereas the means for S. capitata were 0.48 and 0.50, respectively. Roger’s genetic distance varied from 0 to 0.83 for S. macrocephala and from 0 to 0.85 for S. capitata. Analysis with STRUCTURE software distinguished five groups among the S. macrocephala accessions and four groups among those of S. capitata. Nei’s genetic diversity was 27% in S. macrocephala and 11% in S. capitata. Core collections were assembled for both species. For S. macrocephala, all of the allelic diversity was represented by 23 accessions, whereas only 13 accessions were necessary to represent all allelic diversity for S. capitata. The data presented herein evidence the population structure present in the Embrapa-Cerrados germplasm collections of S. macrocephala and S. capitata, which may be useful for breeding programs and germplasm conservation.

Polymorphic microsatellite loci for Stylosanthes macrocephala Ferr. et Costa, a tropical forage legume

Microsatellites were developed for Stylosanthes macrocephala, aiming at developing tools for studying the genetic diversity of this species. A total of 13 polymorphic microsatellite markers were isolated from a S. macrocephala enriched genomic library. The isolated microsatellites were characterized in 20 accessions of the S. macrocephala germplasm collection belonging to the Empresa Brasileira de Pesquisa Agropecuária (Embrapa) Cerrados. The number of alleles per locus varied from 2 to 11, with an average of 4 alleles per locus. The observed and expected heterozygosities ranged from 0 to 0.25 and 0.05 to 0.90, respectively. Cross-amplification of the S. macrocephala polymorphic microsatellites was evaluated in three other Stylosanthes species. The microsatellites reported herein are the first set of microsatellite markers developed for S. macrocephala and are potentially useful for further studies on genetic diversity, conservation and breeding of this species.