Detection of Leptosphaeria Korrae, The Causal Agent of Necrotic Ring Spot, and its Occurrence in Southern Ontario

Isolations from 122 suspected necrotic ring spot (NRS) samples collected throughout southern Ontario, were used to confirm the presence of the disease in the province. Based on morphology of the sexual structures, Leptosphaeria korrae, the causal agent of NRS, was confirmed in 17 Ontario counties. To increase the efficiency of pathogen detection, an assay based on the polymerase chain reaction (PCR), was tested using the primer pair, LK17S/5.8SC, selected from the internal transcribed spacer region 1 of L. korrae ribosomal DNA. Specific amplification of L. korrae DNA was obtained, while no amplification occurred with DNA isolated from 15 other fungal species or healthy Kentucky bluegrass, the major host of NRS. The use of PCR with RAPD (random amplified polymorphic DNA) primers, allowed detection of genetic variability in L. korrae single spore siblings and isolates collected from a single field site. The distribution pattern of polymorphic isolates at the field site suggests both mycelial growth and released ascospores were involved in the spread of NRS.