Influence of flooding and soil properties on the genetic diversity and distribution of indigenous soybean-nodulating bradyrhizobia in the Philippines.

One of the strategies that is commonly used in the Philippines to improve the production of soybean is by inoculation. However, this technique often fails mainly due to the lack of information about the indigenous soybean rhizobia in the Philippines soil. In this study, the diversity of indigenous bradyrhizobia collected from the non-flooded and flooded soil conditions at 11 locations in the country was investigated using a local soybean cultivar as the host plant. The genetic variation among the 424 isolates was detected through Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) treatment and sequence analysis for 16S rRNA gene, 16S-23S rRNA internal transcribed spacer (ITS) region and housekeeping gene. All the isolates were classified under the species namely , , , and a considerable proportion of the isolates were clustered under sp. The isolates which were classified under sp. were thought to be endemic to Philippines soil as evidenced by their nucleotide divergence against the known rhizobia and the historical absence of rhizobia inoculation in the collection sites. The major influence on the distribution and diversity of soybean bradyrhizobia is attributed to the difference in the flooding period, followed by soil properties such as pH, soil type, and nutrient content. As determined, it is proposed that the major micro-symbiont of soybean in the Philippines are for non-flooded soils, then and for flooded soils.