Identification, frequency of occurrence, and inoculum density of select ectotrophic root-infecting fungi within ultradwarf hybrid bermudagrass greens in Mississippi

Gaeumannomyces graminis var. graminis (Sacc.) Arx & Oliver was described as a pathogen of bermudagrass decline [takeall root rot (TARR)]; however, recent studies have reported that multiple ectotrophic root-infecting (ERI) fungi are associated with root rot in ultradwarf hybrid bermudagrass (UDHB) [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy] putting greens. This study surveyed UDHB roots from a healthy and a TARR-symptomatic green. Real-time polymerase chain reaction multiplex assays facilitated the rapid identification and quantification of four ERI fungi: G. graminis, G. nanograminis P.L Vines & M. Tom.-Pet., Magnaporthiopsis cynodontis P.L Vines & M. Tom.-Pet., and Candidacolonium cynodontis P.L Vines & M. Tom.-Pet. Gaeumannomyces nanograminis was identified more frequently than G. graminis in roots from the healthy green and had the greatest inoculum density in 2018. In contrast, G. graminis was identified in 80% more root samples than G. nanograminis in the TARR-symptomatic green in 2017, and the inoculum density of G. graminis was >2 M DNA copies per 2-µl DNA sample. Magnaporthiopsis cynodontis was the predominant fungus in both greens throughout the study; however, its inoculum density was the lowest among all four ERI fungi. Two or more ERI fungi were frequently identified as co-colonizing UDHB roots. This study showed that multiple ERI pathogens were widely distributed throughout the roots of two UDHB greens regardless of symptom expression and confirmed that ERI complexes co-colonize UDHB roots. This is the first study documenting the widespread occurrence and inoculum density levels of multiple ERI fungi colonizing UDHB roots.