Characterization and monitoring of selected rhizobial strains isolated from tree legumes in Thailand

Abstract

Tree legume rhizobia were isolated from five tree legumes; Acacia auriculaformis Cunn., A. mangium Willd., Milletia leucantha Kurz., Pterocarpus indicus Willd., and Xylia xylocarpa Taub. grown in Thailand.
Forty four highly effective rhizobial strains were selected on the basis of nitrogenase activity, number of nodules and plant biomass. The selected strains were characterized in both terms of physiology and
genetics. Most of the strains are slow grower and able to nodulate cowpea rather than soybean. In addition, IAA production could be detected only from few strains. When almost complete 16S rRNA
sequences were analysed, the results indicated that most of the selected strains most likely belong to Bradyrhizobium elkanii and Bradyrhizobium sp. except strains AA67 and PT59 which most likely belong to B. japonicum. The nodule occupancy of selected strains in forest soil condition was investigated by using GUS reporter gene. The nodule occupancy is in the range of 63 - 100%. This suggests the
appropriate strains should be produced as inoculum for further application in reforestation programmes in Thailand.