Unveiling dominant fungal pathogens associated with root rot of hybrid bermudagrass based on culture dependent and independent method

Hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) is widely used as turf in southern and transition zones of China. From June to September in 2022, an unknown disease was consistently observed on hybrid bermudagrass in different regions of Nanjing China, exhibiting distinct symptoms of leaf necrosis, severe root rot and circular or irregular necrotic patches with 20-300 cm in diameter. In this study, culture -independent and dependent methods were used to elucidate the dominant fungal pathogens associated with the disease. Basidiomycota and Marasmiellus were shown to be the dominant phyla (51.96%-70.60%) and genera (50.09%-69.84%) in the symptomatic samples. A total of 128 fungal strains were isolated from symptomatic root tissues, and 40 strains representing the largest proportion (31.25%), were identified as Marasmiellus mesosporus, based on the morphological characteristics, phylogenetic analysis of ITS and LSU rDNA region, and pathogenicity testing. Temperature sensitivity tests revealed that M. mesosporus grew well at high temperature (growth rate of 13.74 mm/d at 36 ℃). To our knowledge, this is the first report of M. mesosporus causing root rot disease on hybrid bermudagrass during hot summer months. The study will have important implications for the management of the disease.