Johnsongrass, yellow foxtail, and broadleaf signalgrass as new hosts for six species of Bipolaris, Curvularia, and Exserohilum pathogenic to bermudagrass.
Since 1999, necrosis and dieback of leaves, stems, and root stunting and plant death were observed on Johnsongrass (Sorghum halepense), broadleaf signalgrass (Brachiaria platyphylla [Urochloa platyphylla]), yellow foxtail (Setaria glauca [Setaria pumila]) in bermudagrass (Cynodon dactylon) pastures in north Mississippi, USA. Symptomatic tissues were surface-sterilized, plated on agar and examined for sporulation. Pathogens were identified by specific morphological features of spores and sporulation as on bermudagrass, and axenic cultures were established by spore transfers to maize meal agar. Bipolaris cynodontis [Cochliobolus cynodontis], Curvularia lunata [Cochliobolus lunatus], Curvularia geniculata [Cochliobolus geniculatus] and Exserohilum rostratum [Setosphaeria rostrata] were isolated from symptomatic leaves of all three grasses and frequently also observed on stems and roots. Bipolaris stenospila was observed only on broadleaf signalgrass and Bipolaris spicifera [Cochliobolus spicifer] on Johnsongrass and yellow foxtail. This is thought to be the first report of the occurrence and pathogenicity for B. cynodontis, C. geniculata and C. lunata on all three grasses, B. stenospila and E. rostratum on broadleaf signalgrass and B. spicifera on Johnsongrass and yellow foxtail.