Diversity and efficiency of bradyrhizobium strains isolated from soil samples collected from around sesbania virgata roots using cowpea as trap species

Abstract

SUMMARYThe genetic diversity of ten Bradyrhizobium strains was evaluated for tolerance to high temperatures, to different salinity levels and for the efficiency of symbiosis with cowpea plants (Vigna unguiculata (L.) Walp.). Eight of these strains were isolated from nodules that appeared on cowpea after inoculation with suspensions of soil sampled from around the root system of Sesbania virgata (wand riverhemp) in ecosystems of South Minas Gerais. The other two strains used in our analyses as references, were from the Amazon and are currently recommended as cowpea inoculants. Genetic diversity was analyzed by amplifying repetitive DNA elements with the BOX primer, revealing high genetic diversity with each strain presenting a unique band profile. Leonard jar assays showed that the strains UFLA 03-30 and UFLA 03-38 had the highest N 2 -fixing potentials in symbiosis with cowpea. These strains had more shoot and nodule dry matter, more shoot N accumulation, and a higher relative efficiency than the strains recommended as inoculants. All strains grew in media of pH levels ranging from 4.0 to 9.0. The strains with the highest N 2 -fixing efficiencies in symbiosis with cowpea were also tolerant to the greatest number of antibiotics. However, these strains also had the lowest tolerance to high salt concentrations. All strains, with the exceptions of UFLA 03-84 and UFLA 03-37, tolerated temperatures of up to 40 ºC. The genetic and phenotypic characteristics of the eight strains isolated from soils of the same region were highly variable, as well as their symbiotic efficiencies, despite their

Phenotypic and molecular fingerprinting of fast growing rhizobia of field-grown pigeonpea from the eastern edge of the Brazilian Pantanal

“…Previous studies evaluating bacterial isolates of pigeonpea reported a generally low or intermediate resistance to chloramphenicol and a high susceptibility to kanamycin (Anand and Dogra, 1991;Fernandes et al, 2003;Fernandes Jr. et al, 2012). Other studies also showed that cowpea and common bean rhizobia also presented intermediate to low resistance to kanamycin, as was observed in the present study; however, these isolates presented a low resistance to chloramphenicol (Xavier et al, 1998;Souza et al, 2003;Zilli et al, 2004;Florentino et al, 2010). Souza et al (2003) reported that Rhizobium tropici and E. fredii showed low resistance to chloramphenicol and to kanamycin, indicating that the majority of the bacterial isolates obtained in the present study should not belong to these species or to related groups.…”

“…Evaluations of the diversity of rhizobial strains using phenotypic characterization combined with molecular fingerprinting have revealed the great diversity in strains isolated from different Brazilian regions from cowpea (Zilli et al, 2004;Leite et al, 2009;Florentino et al, 2010), yam bean (Freitas et al, 2007), and common bean (Stocco et al, 2008). In the Brazilian Pantanal, studies evaluating the diversity of nodule-forming bacteria with phenotypic and molecular methods remain scarce in spite of the great diversity of the plant cover in the region.…”

Legume Crops, Importance and Use of Bacterial Inoculation to Increase Production

“…The occurrence of a wide diversity of microorganisms in a particular soil increases the opportunity for a legume host to find compatible rhizobia. The principle of specific legumerhizobia association is commonly used for the isolation of well adapted and efficient rhizobial strains (Castro-Sowinski et al, 2002;Florentino et al, 2010). Usually trap-plants are used to catch the rhizobial strain with highest performance and the strain is used for the design of new inoculants.…”

Phenotypic diversity and amylolytic activity of fast growing rhizobia from pigeonpea [Cajanus cajan (L.) Millsp.]

“…: 56302-970, Petrolina-PE, Brasil. ; E-mail: paulo.ivan@embrapa.br metabolism, high temperature and salt tolerance (11,12,17,29).…”