Ribosomal ITS sequence-directed selection for endophytic Myrothecium strains antagonistic to Ralstonia solanacearum to control patchouli bacterial wilt.

Ralstonia solanacearum (RS) wilt is a soil-borne devastating disease that causes enormous loss to patchouli in tropical and subtropical areas of Asia. The aim of this study was to develop a feasible method to isolate antagonistic fungal endophytes against RS from patchouli and to investigate their effects on biocontrol of patchouli RS wilt. Diversity of endophytic fungi in roots, stems and leaves of healthy patchouli was estimated with Illumina-based sequencing strategies. The number of fungal operational taxonomic units (OTUs) at 97% similarity level was 465, 542 and 298 in roots, stems and leaves, respectively. The most detected genus in patchouli stems and leaves was Aspergillus, while the most dominant genera in roots were Athelia (11.1%) and Myrothecium (10.1%). Due to wide applications of Myrothecium species for biocontrol, 40 isolates of Myrothecium were isolated from patchouli roots using the selection medium for Myrothecium. At the species level, the strain (SWG1) with the most potent activity against RS in vitro was further identified and used to control patchouli RS wilt in vivo. The results of pot experiments showed that fresh weight, dry weight and height of patchouli seedlings inoculated with SWG1 increased by 58.2%, 65.5% and 11.9%, respectively, compared to seedlings without inoculation. The inoculation of SWG1 reduced the disease incidence and disease index of patchouli RS wilt by 66.7% and 71.0%, respectively. The results indicated the directed isolation of antagonistic endophytic fungi based on Illumina sequencing analysis of the ribosomal fungal ITS should be valuable to screen biological agents to control plant diseases. [ABSTRACT FROM AUTHOR]