Red Rust of Neoregelia Bromeliads Caused by a Parasitic Alga Cephaleuros parasiticus in Florida

A newly emerging disease affecting proprietary hybrids of Neoregelia bromeliads was found in nursery production throughout south Florida. Initial symptoms appeared as small, reddish leaf spots with signs of fungal-like growth on the abaxial leaf surface closely resembling a rust. Closer examination of diseased tissue revealed the growth to be an alga with morphological and molecular characteristics of Cephaleuros parasiticus. This genus of plant parasitic thalloid green algae occurs worldwide in tropical and subtropical regions. Isolates of C. parasiticus collected from Neoregelia hybrid bromeliads were compared with two common Cephaleuros spp. (C. parasiticus and C. virescens) causing leaf spots on guava (Psidium guajava) in south Florida. Further, pathogenicity tests were conducted on healthy Neoregelia hybrids using C. parasiticus isolates collected from diseased leaves of bromeliads and guava. Isolates from both sources produced symptoms consistent with those originally described as “red rust” on Neoregelia hybrids. Florida has 165 plant species belonging to 53 families that have been reported as hosts of Cephaleuros spp., but this is the first report on Neoregelia hybrid bromeliads.