Isolation and identification of nitrogen-fixing bacteria associated with Dioscorea alata L. and Dioscorea esculenta L.

Abstract

Yams are important tuber crops in the tropics. Nitrogen is one of the limiting factors in yam production. Yam accessions that can rely on biological nitrogen fixation must be identified if we are to achieve efficient and sustainable yam production. The aim of this study was to isolate and identify the endophytic diazotrophic bacteria of 19 accessions of two yam species. Forty-one endophytic bacteria were isolated from surface-sterilized roots, stems and leaves of yam accessions grown in nutrient-poor subsoil for 160 days. The 16S rRNA gene sequencing showed that the 41 isolates were grouped into 18 genera including Bacillus, Bradyrhizobium, Devosia, Ensifer, Mycobacterium, Neorhizobium, Paenibacillus, Pseudoxanthomonas, Rhizobium and Xanthomonas. Most endophytes showed a positive response to nitrogenase activity and were found in the stems (21) and the roots (14), while only six were found in the leaves. In Dioscorea esculenta, the acetylene reduction assay (ARA) values ranged from 4.1 to 57.4 nmol tube/24 h and from 4.1 to 164 nmol tube/24 h in Dioscorea alata. In addition, the endophyte species were different among yam species and among yam accessions and were affected by fertilization. These results indicate that the endophytic diazotrophic bacteria of yams are diverse.