Phylogenetic evaluation of Bipolaris and Curvularia species collected from turfgrasses

Abstract

The dothideomycete genera Bipolaris and Curvularia are important pathogens of grasses (Poaceae) and can associate with host tissues without disease symptoms. Species of both genera are responsible for leaf spot epidemics that commonly occur on turfgrass throughout the United States transition zone and southern regions. Recent species typifications with DNA sequences have made a broad examination of Bipolaris and Curvularia species obtained from turfgrass possible. Isolates for analysis were obtained from culture collections or isolated from symptomatic turfgrass samples. Phylogenies based on ITS, GPD , and TEF gene sequences were constructed using maximum likelihood and Bayesian analyses and used to determine intraspecific and intrageneric relationships among Bipolaris and Curvularia species isolated from turfgrasses. Similar to previous studies, Bipolaris and Curvularia species formed separate, well‐supported clades. Morphological identifications of genera and species based on published host‐based keys often disagreed with molecular groupings. For example, C. hawaiiensis (= B. hawaiiensis ) could not be differentiated from B. cynodontis while C. australiensis (= B. australiensis ) could not be differentiated from C. spicifera (= B. spicifera ). Additionally, phylogenies suggest B. coffeana and B. cynodontis are synonymous. However, the number of pseudosepta per conidium was the only consistent morphological character. The delineation of species causing leaf spot diseases of warm‐season turfgrasses should improve disease management decisions and help identify potential pathogens in asymptomatic tissues.