Genetic Variability and Symbiotic Efficiency of Erythrina velutina Willd. Root Nodule Bacteria from the Semi-Arid Region in Northeastern Brazil

Abstract

Legume-rhizobia symbiosis is a cross-kingdom association that results in large amounts of nitrogen incorporated in food webs. For the Brazilian semi-arid region, data on genetic variability and symbiotic efficiency of Papilionoidae rhizobial communities are very scarce. The aim of this study was to evaluate the genetic variability and the symbiotic efficiency of eight rhizobial isolates obtained from "mulungu" (Erythrina velutina Willd.) nodules. For 16S rRNA gene sequencing, the genomic DNA was extracted using a commercial kit, amplified with universal primers, and subjected to sequencing reactions. For the isolate ESA 71, PCR amplifications for nodC and nodA genes were attempted. Rhizobial efficiency was assessed by two greenhouse experiments. The first assay was carried out under gnotobiotic conditions, with sterile sand as a substrate; the second experiment was conducted in a non-sterile soil. For both experiments, the inoculation treatments consisted of a single inoculation of each isolate, in addition to a treatment with Bradyrhizobium elkanii BR 5609 as a reference strain. Furthermore, two non-inoculated control treatments, supplied and not supplied with mineral N, were also evaluated. Bacterial identification indicated that both α and β-rhizobia could be found in "mulungu" root nodules. Three isolates where classified within the Rhizobium genus, four bacteria belonged to Bradyrhizobium and one isolate clustered with Burkholderia. Positive amplification of an intragenic fragment of the nodA gene using a primer set to β-rhizobia could be found for ESA 71 (Burkholderia). All bacterial isolates were effective in colonizing "mulungu" roots. In the first experiment, all inoculated treatments and N fertilization increased the N concentration in "mulungu" shoot tissues. For total N in the shoots, the isolates ESA 70, ESA 72, and ESA 75 stood out. In the non-sterile substrate experiment, the isolates ESA 70, ESA 71, ESA 72, and ESA 75, together with the reference strains, induced increases in the shoot N concentration and total accumulation compared to the absolute control. The results indicate that "mulungu" is able to establish associations with efficient α and β-rhizobia in Brazilian semi-arid soils.

Symbiotic efficiency of native rhizobia in legume tree Leucaena leucocephala derived from several soil classes of Brazilian Northeast region

“…The best performance of native isolates compared with the recommended strains and the commercial inoculants has been reported in the literature (Calheiros et al, 2015) with calopogonium species, using isolates native to Northeast Brazil (84 to 131%). Menezes et al (2017) reported the the highest competitive potential among several rhizobia isolates by Erythrina velutina, which is native to Brazilian semiarid regions compared to the recommended strain. They observed a very positive effectiveness of the native rhizobia.…”

“…The height and diameter of plants have been recently used for evaluation of symbiotic efficiency of rhizobia in tree legumes (Ceccon et al, 2012;Ramos et al, 2013;Primieri et al, 2016;Menezes et al, 2017). These parameters indicate the quality of the seedlings, the potential of survival and growth after transplanting.…”

“…Ten days after sowing only one seedling were left in each pot. The inoculation was performed according to Menezes et al (2017), pipetting 1 ml (10 9 cfu/ml) of the respective rhizobia isolates for seed. The growth of L. leucocephala was evaluated by measuring the height and the diameter of the shoots, using a ruler and a digital caliper, respectively.…”

“…However, few studies were conducted to evaluate the effectiveness of native isolates in nodulation of tree legume (Erythrina velutina Willd.) (Menezes et al, 2017).…”

Phenotypic, genetic and symbiotic characterization of Erythrina velutina rhizobia from Caatinga dry forest

“…Recent studies showed that Erythrina velutina Willd., commonly known as “mulungu”, is able to establish symbiotic association with rhizobia in soils from the Brazilian Semi-Arid. 16 , 17 E. velutina , classified within the Papilionoidae clade and Phaseoleae tribe, is a naturally inhabiting tree from the Northeast region of Brazil. This species is used as wood, timber, ornamental applications and sources of bioactive compounds with pharmacological applications.…”