Isolation, identification and phylogenetic analysis of endophytic nitrogen-fixing bacteria from sweet potato tuberous root

【Objective】 The purpose of the study was to molecularly identify and analyze the diversity of endophytic nitrogen-fixing bacteria in tuberous roots of sweet potato, and to analyze their flora structure, so as to provide theoretical reference for further research on the application of endophytic nitrogen-fixing bacteria in sweet potato.【Method】 Using Eshu 11 and Eshu 17 as experimental materials, the endophytic nitrogen-fixing bacteria obtained from the tuberous roots of two sweet potato varieties were screened by nitrogen free medium, and the isolated endophytic nitrogen-fixing bacteria were classified and identified according to 16S rDNA gene sequence analysis. The nifH gene fragment was further amplified to verify the nitrogen-fixing bacteria. According to Shannon diversity index, relative isolation rate and similarity index of strains, the distribution and diversity of endophytic nitrogen-fixing bacteria in sweet potato tuberous roots were analyzed, and the differences in endophytic nitrogen-fixing bacterial flora were compared.【Result】 A total of 80 endophytic nitrogenfixing bacteria were isolated from the tuberous roots of Eshu 11 and Eshu 17, which belonged to 1 phylum, 1 class, 1 order, 1 family and 2 genera, including Priestia and Bacillus, with relative isolation rates of 51.25% and 48.75% respectively. The relative isolation rates of Pristeria in tuberous roots of Eshu 11 and Eshu 17 were 51.11% and 51.43% respectively, and the relative isolation rates of Bacillus in tuberous roots of Eshu 11 and Eshu 17 were 48.89% and 48.57% respectively. There was small difference in the relative isolation rate of endophytic nitrogen-fixing bacteria in the tuberous roots of the two sweet potato varieties. The total Shannon index of endophytic nitrogen-fixing bacteria in the tuberous roots of the two sweet potato varieties was 0.6929, and the total evenness index was 0.4803. The similarity index between Eshu 11 and Eshu 17 was 1, and the endophytic nitrogen-fixing bacteria in the tuberous roots of the two sweet potato varieties were of the same genera. The phylogenetic tree showed that the genetic diversity of endophytic nitrogen-fixing bacteria isolated from Eshu 11 and Eshu 17 was low.【Conclusion】 Eighty strains of endophytic nitrogen-fixing bacteria are isolated and identified from Eshu 11 and Eshu 17. The obtained endophytic nitrogen-fixing bacteria belong to Priestia and Bacillus. There is no obvious difference in the composition of endophytic nitrogen-fixing bacteria between the two varieties.