A comparison of Bradyrhizobium strains using molecular, cultural and fieldstudies

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 Bradyrhizobi um and Rhizobium obtained from A. mangium plantations in Sabah, Malaysia, w ere characterised by PCR amplification of ribosomal DNA and RFLP analysis, host spectrum and antibiotic resistance. The Sabah isolates were also compa red with isolates collected from Singapore, Australia, and Africa. The resu lts distinguished two main groups of Bradyrhizobium. Group I strains were p revalent, 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 f ield inoculation trials with A. mangium seedlings showed that the Group I s trains were more effective in enhancing plant growth than Group II strains. (C) 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.