Ocorrência de Mimosa micropteris (Benthan) nodulíferas nativas nos Campos Gerais (Paraná-Brasil) e diversidade genética de seus microssimbiontes

Abstract

Fabaceae is one of the major botanical families, recognized by its species diversity and wide geographical distribution. Floristic surveys performed in the State Park of Vila Velha (Ponta Grossa-PR) pointed out the occurrence of several species of the subfamily Mimosoidae, including Mimosa micropteris Bentham. This study presents the first description of root nodules in M. micropteris and describes the diversity of their rhizobia. Soils of the sample areas were characterized as sandy, acid and low in organic matter. Eighteen strains were obtained from nodules of native plants; all of them are acid-producing in YMA medium, intermediate growers with viscous colonies. Considering a 70% of similarity cutoff, BOX-PCR fingerprint analysis divided the strains in four groups. Group A was the most representative, with six strains, followed by group D, with five strains. Phylogenetic analysis of partial 16S rDNA sequences revealed the relation of strains of all BOX-PCR groups with Paraburkholderia nodosa, indicating intraspecific variability between M. micropteris symbionts. Only one strain was classified as Rhizobium sp. This data corroborates the recent findings that beta-rhizobia are the preferential symbionts of Mimosa in South America. The nodC phylogeny grouped all the strains, including the one classified as Rhizobium sp., into a well-supported clade that not grouped any known strain of the Paraburkholderia genus. Our results demonstrate that M. micropteris can be nodulated both by alpha- and beta-rhizobia, probably due to lateral gene transfer of symbiotic genes. Also, the prevalence of beta-rhizobia corroborates the statement that their superior competitiveness abilities under particular edaphic conditions, as acid pH and low nutrient content.