First report of leaf spot caused by Bipolaris oryzae on switchgrass in Tennessee.
In December 2007, dark brown to black irregularly shaped foliar spots were observed on switchgrass (Panicum virgatum) cv. Alamo at the campus of the University of Tennessee, USA. A sparsely sporulating, dematiaceous mitosporic fungus was observed. Conidia were ovate, oblong, mostly straight to slightly curved, and light to olive-brown with 3-10 septa. Conidiophores were light brown, single, multiseptate, and geniculate. Morphological characteristics and disease symptoms were similar to those described for B. oryzae [Cochliobolus miyabeanus]. The original fungal isolate and the pathogen recovered in the disease assay were identified using internal transcribed spacer (ITS) region sequences. The ITS region of rDNA was amplified with PCR and primer pairs ITS4 and ITS5. PCR amplicons of 553 bp were sequenced, and sequences from the original isolate and the reisolated pathogen were identical (GenBank accession no. JQ237248). The nucleotide sequence was 100% identical to that of B. oryzae from switchgrass in Mississippi (GU222690, GU222691, GU222692 and GU222693) and New York (JF693908). This is thought to be the first report of B. oryzae from switchgrass in Tennessee.