Identification of Species Associated with a New Disease of Annual Bluegrass Putting Greens.

Identification of species associated with a new disease of annual bluegrass putting greens.

Rollo, P. and J.E. Kaminski

Between 2005 and 2017, a potentially new disease of annual bluegrass (Poa annua L.; ABG) has been observed on golf course putting greens in the northeastern United States. Symptoms to ABG include yellow to orange, circular patches ranging from 8 to 30 cm in diameter within mixed stands with creeping bentgrass (Agrostis stolonifera L.). Following incubation, coenocytic mycelium can be observed in the canopy of symptomatic leaves. The objectives of this study were to: 1) identify any pathogenic species associated with symptomatic ABG; 2) determine cardinal temperatures for growth of isolates obtained from symptomatic tissue; and 3) complete Koch’s postulates using collected isolates. A total of 14 isolates collected from 13 golf courses in five states in 2016 were subjected to DNA sequencing. Based on sequence analysis of the ITS region, isolates obtained from symptomatic ABG included Pythium aristosporum (n = 5), P. arrhenomanes (n = 3), P. aphanidermatum (n = 2), Pythium inflatum (n = 1) and Rhizopus oryzae (n = 3). Growth of all isolates was determined on potatoe dextrose agar across six temperatures ranging from 10 to 40C. Maximum growth occurred between 25 and 35C for all isolates with P. arrhenomanes, P. aristosporum, and P. inflatum growing the slowest among all isolates evaluated. Koch’s postulates were also perfomed on six representative isolates from the most commonly observed species including P. arrhenomanes, P. aristosporum, and R. oryzae. Creeping bentgrass and ABG were inoculated and incubated at 25C with a 12 h day/night cycle. The two species of Pythium evaluated caused disease symptoms. Although Pythium infected both turfgrass species, disease severity was greatest on annual bluegrass. Although more information is needed, this purported new disease appears to be caused by a complex of Pythium species and has been termed Pythium patch.