Yellow Ring on Poa pratensis Caused by Trechispora alnicola. H. T. Wilkinson, Assistant Professor of Plant Pathology, Department of Plant Pathology, University of Illinois, Urbana-Champaign 61801. Plant Dis. 71:1141-1143. Accepted for publication 15 July 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-1141.

Trechispora alnicola was identified as the causal agent of yellow ring disease of Poa pratensis. The fungus was isolated from surface-sterilized roots and crown tissues of naturally infected sod. Mycelium and conidia were effective forms of inoculum when placed adjacent to the grass crowns or roots or drenched into sod. Kentucky bluegrass seedlings developed yellowed leaves, typical of yellow ring disease, 6–8 wk after inoculation. Inoculated sod required 16 wk to develop yellowed leaves. Disease severity was greatest at 20 and 25 C, and no disease symptoms developed at 30 C. Bluegrass susceptibility was not affected by maturation; both 3-wk-old and 2-yr-old sod were susceptible. The fungus was capable of saprophytic colonization of naturally produced thatch. The fungus was readily recovered from inoculated grass roots after surface sterilization but not from crown tissue. In culture, the fungus grew most rapidly on thatch agar medium at 20–25 C and was capable of growth at 15 and 32 C.