Isolation, identification, and pathogenicity determination of fungal pathogens causing root rot of Stipa bungeana in Inner Mongolia, China.

Stipa bungeana Trin. is a dominant grass species in the warm temperate steppes of northern China; however, its root rot diseases have not been systematically investigated. In this study, 100 root samples of S. bungeana showing typical root rot symptoms were collected from the Sha'erqin Research Base in Tumd Left Banner, Hohhot City, Inner Mongolia, China. A total of 76 fungal isolates, were recovered and identified based on morphological characteristics and multi-locus sequence analysis of the internal transcribed spacer (ITS) region, translation elongation factor 1-alpha (TEF1-α), and the second largest subunit of RNA polymerase II (RPB2) gene. Eight species were identified, of which Curvularia spicifera (25 isolates, 32.89%) and Microdochium bolleyi (24 isolates, 31.58%) were the predominant species. Pathogenicity tests conducted on healthy S. bungeana seedlings under greenhouse conditions demonstrated that all 8 species induced root rot symptoms, thereby, fulfilling Koch's postulates. Notably, C. spicifera and M. bolleyi exhibited significantly greater virulence than the Fusarium species and the other recovered fungi, resulting in higher disease incidence and plant mortality. This study represents the first comprehensive report of the fungal pathogens associated with root rot of S. bungeana in China and provides the first evidence that C. spicifera and M. bolleyi are the predominant and most virulent pathogens associated with root rot of Stipa species. These findings fill an important critical knowledge gap in grassland plant pathology and provide a scientific foundation for disease management in natural steppe ecosystems.