c Among the leguminous trees native to Uruguay, Parapiptadenia rigida (Angico), a Mimosoideae legume, is one of the most promising species for agroforestry. Like many other legumes, it is able to establish symbiotic associations with rhizobia and belongs to the group known as nitrogen-fixing trees, which are major components of agroforestry systems. Information about rhizobial symbionts for this genus is scarce, and thus, the aim of this work was to identify and characterize rhizobia associated with P. rigida. A collection of Angico-nodulating isolates was obtained, and 47 isolates were selected for genetic studies. According to enterobacterial repetitive intergenic consensus PCR patterns and restriction fragment length polymorphism analysis of their nifH and 16S rRNA genes, the isolates could be grouped into seven genotypes, including the genera Burkholderia, Cupriavidus, and Rhizobium, among which the Burkholderia genotypes were the predominant group. Phylogenetic studies of nifH, nodA, and nodC sequences from the Burkholderia and the Cupriavidus isolates indicated a close relationship of these genes with those from betaproteobacterial rhizobia (beta-rhizobia) rather than from alphaproteobacterial rhizobia (alpha-rhizobia). In addition, nodulation assays with representative isolates showed that while the Cupriavidus isolates were able to effectively nodulate Mimosa pudica, the Burkholderia isolates produced white and ineffective nodules on this host.
Parapiptadenia rigida (Benth.) Brenan, which is also known by its vernacular names Angico, Angico vermelho, and Gurucaia, belongs to the tribe Mimoseae within the Mimosoideae subfamily of the Fabaceae (Leguminosae) (5,26,27,38). It is native to southern South America (south Brazil, Argentina, Paraguay, and Uruguay), where it can be found as one of the tallest species in the canopy of riverside forests, where it can reach heights of approximately 30 m and breast height diameters of from 30 to 120 cm. The wild tree is currently exploited by the locals owing to its economic value, although commercial cultivation of P. rigida has never been developed in Uruguay. Its main economic value is based on the excellence of its timber, which is appreciated for its high density (0.74 to 0.98 g/cm 3 ) and natural durability (26). It is mostly used for high-quality furniture, house construction, carpentry, and fire wood, and the reddish brown parquet floors built with its timber are deeply valued. Other reported uses are as a source of gums, tannins, and essential oils as well as for medicinal purposes (14, 37). Indeed, it is much appreciated by people in Brazil for its medicinal qualities and is duly included in the Brazilian Pharmacopeia.This heliophyte species is part of the forest succession during the first steps of recovery of degraded areas, as it can grow under adverse and low-soil-fertility conditions. Its ability to establish a nitrogen-fixing association with rhizobia is well documented (18)(19)(20)32), but information about the rhizobia associated with this leguminous...
