Presença e eficiência de Rhizobium Japonicum em solos cultivados ou não com soja, no estado deSão Paulo

Abstract

ELI SIDNEY LOPES e ANTÔNIO ROBERTO GIARDINI, Seção de Microbiologia doSolo, e ROMEU A. S. KIIHL ( 2 ), Seção de Leguminosas, Instituto Agronô-mico SINOPSEFoi conduzido um ensaio em solução nutritiva sem nitrogênio, com condições assépticas, usando-se como inoculantes para as plantas amostras de solos LR e LB coletadas em locais já cultivados e não com soja, com o objetivo de verificar a presença de Rhizobium capaz de nodular o cultivar santa-rosa.Verificou-se que solos ainda não cultivados com a leguminosa são desprovidos de Rhizobium japonicum, e também que essa bactéria é encontrada em solos previamente cultivados, fixando nitrogênio em quantidades equivalentes à de uma estirpe selecionada.

Genetic diversity of indigenous tropical fast-growing rhizobia isolated from soybean nodules

“…Brazilian soils are originally void of rhizobia able to effectively nodule soybean (e.g., Lopes et al 1976;Peres 1979;Vargas and Suhet 1980;Ferreira and Hungria 2002;Hungria et al 2006), therefore inoculants carrying Bradyrhizobium were brought mainly from the USA; S. fredii has never been used in Brazilian inoculants . The presence of fast-growing rhizobial strains in soybean nodules in Brazil had never been reported, until in a survey carried out using one modern and six Asian soybean genotypes as trap hosts, thirty fastgrowing isolates were obtained from twelve soils throughout Brazil; those strains were preliminary characterized in relation to morphological, physiological (Hungria et al 2001b), and symbiotic (Hungria et al 2001a) properties.…”

Characterization of soybean Bradyrhizobium strains adapted to the Brazilian savannas

“…Brazilian soils are usually very poor in N and are originally free of soybean bradyrhizobia [8,13,15,16,29,30]. Therefore, with the introduction of the soybean crop to the country, inoculants containing foreign strains were used.…”

“…Until now, the identification of strains by the Brazilian laboratories has been based exclusively on the serological properties and well defined groups with different serological reactions have been established. It is possible that foreign inoculants used in Brazil during the first years of the crop's introduction carried contaminant strains, but for years the serological analysis of nodules collected in the field showed that the known strains occupied most of the nodules [8,10–13,16–20,29–32]. To be able to establish in the soil in such high proportions, these contaminant strains should be extremely competitive and dissemination from other producing areas would have occurred.…”

“…Soybean was introduced into Brazil in the last century, but large‐scale commercial crop production started in the early 1960s. As Brazilian soils are originally free from soybean bradyrhizobia [8,13,15,16,29,30], during the establishment of the crop, the seeds had to be inoculated with strains. The inoculant strains were initially brought from the USA, but a search for strains adapted to Brazilian conditions started concomitantly with the expansion of commercial soybean crop production [6,8,15,16,18,19].…”

“…As Brazilian soils are originally free from soybean bradyrhizobia [8,13,15,16,29,30], during the establishment of the crop, the seeds had to be inoculated with strains. The inoculant strains were initially brought from the USA, but a search for strains adapted to Brazilian conditions started concomitantly with the expansion of commercial soybean crop production [6,8,15,16,18,19]. The selection of adapted strains usually consisted of inoculation of an area, followed, after a short period of time, by reisolation of bacteria from nodules of soybean trap plants.…”