Genetic diversity of rhizobia in a Brazilian oxisol nodulating Mesoamerican and Andean genotypes of common bean (Phaseolus vulgaris L.)

Abstract

Brazil is the largest producer and consumer of common bean worldwide, and the crop can benefit from its symbiosis with a variety of rhizobia by means of biological nitrogen fixation in root nodules. In this study, the role of Mesoamerican and Andean genotypes of common bean in trapping rhizobia directly from a Brazilian oxisol in the field or in pots in greenhouse conditions with unaltered or diluted soil solutions was investigated. Genetic diversity was evaluated by the profiles of BOX-PCR obtained, and by estimates of Shannon and Abundance-based Coverage Estimator (ACE) indices. Rhizobia trapped by Mesomaerican genotypes had greater diversity, reinforcing the hypothesis of an important and long-time contribution of this genetic center to the establishment of common bean in Brazil. Greater diversity was also seen in rhizobia trapped straight from the soil than from plants inoculated with diluted soil solutions, emphasizing a highly diverse and competitive rhizobial indigenous population. Studies on genetic diversity of common bean rhizobia are important not only for helping to understand the evolution of the legume-rhizobia symbiosis, but also to devise strategies to increase the contribution of the biological nitrogen-fixation process.

Common bean elite lines cultivated under nitrogen fertilization and inoculation with Rhizobium tropici

“…Results confirm the finding that the response to BNF in common beans is dependable upon environmental conditions and lines as well as upon the Rhizobium strains (OLIVEIRA et al, 2011;CARDOSO et al, 2012).…”

“…This fact has been attributed to the susceptibility of both symbiotic organisms to several environmental factors such as high temperatures and low soil humidity, among others (HUNGRIA et al, 2000b;OLIVEIRA et al, 2011). To overcome these limitations, several studies have been conducted to identify strains of Rhizobia more efficient to BNF (CARDOSO et al, 2012).…”

Genetic and phenotypic diversity of Rhizobium isolates from Southern Ecuador

“…Similar to this study, R. etli, R. leguminosarum and R. tropici have been previously isolated from common bean nodules (Martínez-Romero, 2003;Aguilar;Riva;Peltzer, 2004;Oliveira et al, 2011) and are considered to be the predominant occupant species of bean nodules in the Andean region (Junier et al, 2014;Ribeiro et al, 2015). Ecuador, north of Peru, Colombia and the Andean Region are currently considered to be the centers of domestication/diversity of the common bean (Oliveira et al, 2011). Thus, it is important to isolate native strains from this region to determine their ability to fix nitrogen, and stimulate bean plants to obtain inoculants that provide benefits to farmers.…”

“…Although few studies have reported on the genetic diversity of Rhizobium in Ecuador (Ribeiro et al, 2013), this is the first report of species diversity in the southern region of the country. Similar to this study, R. etli, R. leguminosarum and R. tropici have been previously isolated from common bean nodules (Martínez-Romero, 2003;Aguilar;Riva;Peltzer, 2004;Oliveira et al, 2011) and are considered to be the predominant occupant species of bean nodules in the Andean region (Junier et al, 2014;Ribeiro et al, 2015). Ecuador, north of Peru, Colombia and the Andean Region are currently considered to be the centers of domestication/diversity of the common bean (Oliveira et al, 2011).…”

Morphophysiological characterization of rhizobia isolated from wild genotypes of the common bean

“…Nevertheless, high morphological diversity was observed among the obtained isolates, whereas the isolates showed unusual characteristics for the genus Rhizobium, such as neutral pH, slow growth and small production of mucus (Figure 1). High morphological diversity among the common bean rhizobia isolates has been reported in Brazil (HUNGRIA et al 2000;MOSTASSO et al 2002;OLIVEIRA et al 2011), reinforcing reports about the promiscuity of the common bean to establish association with the rhizobia soil community (OLIVEIRA et al 2011). …”