DETERMINATION OF AN ETIOLOGIC AGENT OF BERMUDAGRASS DECLINE

Gaeumannomyces graminis var. graminis, G. incrustans and Phialophora spp. have been isolated in Florida from bermudagrass putting greens with bermudagrass decline symptoms. Using a containerized test system, G. g. graminis isolates, but not G. incrustans or Phialophora spp. isolates, were pathogenic to hybrid bermudagrass. A Magnaporthe poae isolate, obtained from bentgrass turf grown in Florida, also was pathogenic to bermudagrass. However, M. poae has not been identified from bermudagrass in nature. For both G. g. graminis and M. poae, the plant growth conditions and turfgrass host and geographic location of the isolates did not affect pathogenicity. Wheat pathogenicity assays also were conducted for all the isolates to develop a quick assay for determining pathogenicity. Results from the wheat and bermudagrass pathogenicity assays correlated well for G. g. graminis, M. poae, and Phialophora spp. but not for G. incrustans. This wheat assay also permitted tentative identification of the fungi. Preliminary results indicate that these ectotrophic fungi are introduced into new putting greens on the bermudagrass sprigs used for green establishment.