A comparison of Bradyrhizobium strains using molecular, cultural and field studies

Abstract

Acacia mangium is a leguminous tree used in industrial plantations for the production of pulp wood, and for the rehabilitation of degraded soils. Its ability to grow in very poor soils is due to its symbiotic association with nitrogen-fixing Bradyrhizobium. In this study, 33 isolates of Bradyrhizobium and Rhizobium obtained from A. mangium plantations in Sabah, Malaysia, were characterised by PCR amplification of ribosomal DNA and RFLP analysis, host spectrum and antibiotic resistance. The Sabah isolates were also compared with isolates collected from Singapore, Australia, and Africa. The results distinguished two main groups of Bradyrhizobium. Group I strains were prevalent, widely dispersed but genetically closely related. They were also closely related to the Singapore and Australian strains. Strains from Group II were less widely dispersed and more distantly related. Greenhouse and field inoculation trials with A. mangium seedlings showed that the Group I strains were more effective in enhancing plant growth than Group II strains.