ABSTRACT
Legume root symbiotic bacteria, now collectively known as rhizobia, were fi rst described by Beijerinck in 1888, and later isolated from the root nodules of many legumes. With the introduction of soybean in the U.S.A., it was demonstrated that the culture only succeeded if their root nodule symbiotic bacteria were also introduced. Although then known as Rhizobium japonicum, these bacteria were quite different from other rhizobia: they were larger, grew slowly and did not acidify sugar-containing media. Similar bacteria were later isolated from other legumes, such as lupines, cowpeas, and many tropical trees and shrubs, and were eventually grouped into a separate genus, Bradyrhizobium. Despite its large diversity (see below), most
1Centre for Plant Biotechnology and Genomics (CBGP), Universidad Politécnica de Madrid and INIA, Campus de Montegancedo, Ctra. M-40, km 38, 28223 Pozuelo de Alarcón, Madrid (Spain). 2 C.S.I.C *Corresponding author: t.ruizargueso@upm.es
studies have been performed on B. japonicum, undoubtedly because of the importance of soybean as a crop.
