Occurrence of endophytic bacteria in Vietnamese Robusta coffee roots and their effects on plant parasitic nematodes

Several plant parasitic nematode genera were identified in the Robusta coffee (Coffea canephora Pierre ex A. Froehn) tree roots and surrounding soil samples from three different coffee groups: coffee planted at 5 years (CYG), 18 years (CBG) and 40 years (COG) in Central Highland, Vietnam. They included Meloidogyne spp., Pratylenchus spp., Apratylenchus spp., Criconemella spp., Xiphinema spp. and Rotylenchulus spp. Meloidogyne spp. was the most abundant genus, at 77% across all three groups. Endophytic bacteria were isolated from healthy tissues of roots of the same Robusta coffee trees. In total, 77 bacterial strains were isolated and determined to be Bacillus spp., Serratia spp., Paenibacillus spp., Enterobacter spp. and Streptomyces spp. based on colony morphological and 16S rRNA gene sequence analysis. Overall, Streptomyces was the dominant genus and accounted for 49.35% of total isolated strains. Using statistical methods, we found a tendency in the abundance of endophytic bacterial isolates with the elevation or decrease of several nematode populations, indicating a relation between endophytic bacteria occurrence and nematode distribution. In in vitro anti nematode screening test, a Streptomyces sp. strain named CBG9 showed significant nematicidal activities against Meloidogyne incognita, inhibiting egg hatching (85.8%) and causing mortality of secondary stage juveniles (85%). This study explored the anti-nematode potency of endophytic bacteria isolated from coffee trees, which could provide a future application in suppression and management of pathogenic nematodes without the use of chemical pesticides.