Rhizobitoxine production and symbiotic compatibility of Bradyrhizobium from Asian and North American lineages of amphicarpaea.

Reciprocal inoculations with Bradyrhizobium sp. isolates from the North American legume Amphicarpaea bracteata (L.) Fern. (Phaseoleae-Glycininae) and from a Japanese population of its close relative Amphicarpaea edgeworthii (Benth.) var. japonica were performed to analyze relative symbiotic compatibility. Amphicarpaea edgeworthii plants formed few or no nodules with any North American bradyrhizobial strains isolated from A. bracteata, but all A. bracteata lineages formed effective nitrogen-fixing nodules with Japanese Bradyrhizobium isolates from A. edgeworthii. However, one group of A. bracteata plants (lineage Ia) when inoculated with Japanese bradyrhizobia developed a striking leaf chlorosis similar to that known to be caused by rhizobitoxine. The β-cystathionase inhibition assay demonstrated that significant amounts of rhizobitoxine were present in nodules formed by these Japanese bradyrhizobia. No North American bradyrhizobial isolate from A. bracteata induced chlorosis on any plants, and the β-cysta...