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Title: First report of infection of bermudagrass by Bipolaris sorokiniana in the southeastern USA

item Pratt, Robert

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2003
Publication Date: 10/1/2003
Citation: Pratt, R.G. 2003. Morphology and pathogenicity of Bipolaris sorokiniana from bermudagrass in Mississippi. Plant Disease. 87:1265.

Interpretive Summary: Animal waste application sites are fields where wastes (manure, urine) from large-scale animal feeding operations (swine, poultry) are applied for disposal. Maximal growth of forage grasses is required on these sites to absorb excess nutrients from wastes and prevent their movement into water to cause pollution. Fungal diseases that reduce growth of bermudagrass on waste-disposal sites prevent maximal forage production and pollution control. When new diseases are discovered on forage grasses in these situations, their identities and potentials for causing losses must be determined. In this study, a new disease-causing fungus was identified for the first time in eastern North America on bermudagrass on three swine waste application sites in Mississippi. This fungus was previously known to damage ryegrass, wheat, and other cool-season grasses in this region, but it was not known to attack bermudagrass. The new fungus was found on bermudagrass throughout the summer growing season. Strains of the fungus from bermudagrass were similar or identical to strains from ryegrass, and strains from both sources caused severe damage to bermudagrass when evaluated for disease-causing ability on excised leaves or whole plants. They also caused more damage than a related fungus that commonly occurs on bermudagrass. These results show that the same fungus that attacks cool-season grasses can also infect a warm-season grass, bermudagrass, throughout the summer growing season. This fungus might seriously reduce forage production by bermudagrass if it becomes widespread on account of its ability to cause severe symptoms in infected plants. It is now known that the same fungus also may spread between bermudagrass and ryegrass when growth periods of these warm- and cool-season species overlap.

Technical Abstract: Bipolaris sorokiniana, a major pathogen of small grains and cool-season grasses, was observed repeatedly on common bermudagrass [Cynodon dactylon (L.) Pers.], a warm-season perennial, on three swine waste application sites in Mississippi in 2002. This represents the first report of B. sorokiniana on bermudagrass in the eastern USA. Morphological features and pathogenicity of isolates from bermudagrass and ryegrass, a common cool-season host, were compared to determine whether the same strain of the pathogen infects both species. Single-spore isolates of B. sorokiniana from bermudagrass and ryegrass differed significantly in growth rate, sporulation, and length of conidia, but differences were not consistently related to hosts of origin. Individual isolates of B. sorokiniana from bermudagrass and ryegrass, and of B. cynodontis from bermudagrass, differed in severity of symptoms induced in excised bermudagrass leaves following mycelial inoculations on plates of agar, but differences were not consistently related to fungal species or host of origin. Isolates of B.sorokiniana from bermudagrass and ryegrass induced symptoms that were similar in severity, and significantly more severe than symptoms induced by B. cynodontis, in foliage of bermudagrass inoculated with spores at similar concentrations. Results indicate that the same strain of B. sorokiniana infects both ryegrass and bermudagrass in Mississippi; that virulence of B. sorokiniana on bermudagrass is greater than that of the common bermudagrass pathogen, B. cynodontis, with spore inoculations; and that a potential exists for epidemiological relationships between diseases caused by B. sorokiniana on bermudagrass and cool-season species overseeded upon it.