Interactions with Rhizobia in the Species of Lespedeza Section Juncea (Fabaceae) in Japan

Abstract

Legume species are typically associated with specific rhizobial symbionts. Section Juncea of genus Lespedeza (Fabaceae) is a suitable system for the study of the levels of specificity in interactions between legumes and rhizobia because various levels of specificity have been seen among species in China and species within this section sometimes co-occur geographically. We examined the rhizobial compositions of four taxa of Lespedeza sect. Juncea, namely L. cuneata var. cuneata, L. cuneata var. serpens, L. pilosa, and L. tomentosa. We isolated rhizobia from nodules of wild-grown plants and identified them through partial sequencing and/or PCR-RFLP pattern of 16S rRNA gene. In total, 815 strains were identified as rhizobia to the genus or species group level; 96.2% of them are identified as Bradyrhizobium (where 44.9% were identified as B. japonicum group and 51.3% were identified as B. elkanii group). The compositions of those Bradyrhizobium groups differed among Lespedeza taxa. Strains of the B. japonicum group were isolated more frequently than those of the B. elkanii group from L. cuneata var. cuneata. In contrast, strains of the B. elkanii group were isolated more frequently than those of the B. japonicum group from L. tomentosa and L. cuneata var. serpens. Lespedeza pilosa showed the most conspicuous interaction with rhizobia, where 90.9% of isolates were identified as B. elkanii group. Although the factors controlling the specificity to certain rhizobia remain unknown, characteristic rhizobial compositions were detected in all of the Lespedeza taxa examined in this study.