Reactive Oxygen Species Production and Alternative Hosts of Spring Dead Spot–Causing Fungi

Three fungi in the genus Ophiosphaerella ,— O. herpotricha, O. korrae , and O. narmari —are the causal agents of spring dead spot of bermudagrass. The extent to which Ophiosphaerella spp. can colonize and infect other plant hosts and the mechanism by which they render host cells necrotic remain unknown. In other plant–pathogen interactions, it has been shown that the hypersensitive response (HR), initiated by the formation of reactive oxygen species (ROS) in the host, can promote the infection of necrotrophic fungi. The objectives of these studies were to investigate the formation of ROS during infection of plant cells and to characterize the host range of Ophiosphaerella spp. To assess ROS production, roots of three bermudagrass cultivars—Tifway 419, Midlawn, and U3—were each inoculated with an isolate of either O. herpotricha or O. korrae. The roots were stained with 2′,7′‐dichlorofluorescein diacetate at 4 to 74 h after inoculation. Staining of root cells indicated formation of ROS in response to fungal infection. The cultivar U3, which is tolerant to spring dead spot, is more likely to form high levels of ROS than the interspecific hybrid cultivars Midlawn and Tifway 419. To determine the potential host range of O. herpotricha and O. korrae , several warm‐season grasses, cool‐season grasses, and dicotyledonous plants were evaluated for colonization at 2 to 14 d after inoculation. The colonization process was similar for O. herpotricha and O. korrae on most plant species tested. Grass plant roots were readily colonized, and some showed symptoms of necrosis. The dicot plants evaluated were nonhosts. Significantly higher ROS production by the tolerant bermudagrass cultivar U3 suggests that root necrosis caused by Ophiosphaerella spp. is independent of HR associated with plant‐generated ROS. Colonization studies show that these fungi have a broad monocotyledonous host range.