Identification and characterization of Pythium graminicola, causal agent of kikuyu yellows in Argentina

Kikuyu grass (Pennisetum clandestinum) is a perennial plant that belongs to the Poaceae family. In Argentina, it is used in warm areas as tropical pasture, forage and grass in gardens and sports fields. Species of Pythium have a cosmopolitan distribution and are important pathogens of a wide range of plant hosts. In the spring of 2009, a new disease affected areas cultivated with kikuyu grass in different parks located near the city of Buenos Aires. The symptoms were an evident chlorosis of leaves, which got circular as the affected area expanded, followed by severely rotten roots and blighting. The aim of this study was to identify the causal agent of kikuyu yellows in Argentina. An oomycete was consistently isolated from diseased tissues. The pathogen was identified as Pythium graminicola based on cultural characteristics and the morphology of vegetative and reproductive structures. Phylogenetic analyses were performed based on combined sequence datasets of the internal transcribed spacer of the nuclear rDNA and the beta tubulin gene. Pathogenicity tests were carried out and Koch’s postulates were fulfilled. This is the first report of P. graminicola causing kikuyu yellows in Argentina and in the world.