First report of Fusarium thapsinum Klittick affecting switchgrass inflorescences in state of Yaracuy, Venezuela

Abstract

Fusarium  thapsinum  is reported  for the first time affecting  Brachiaria  humidicola  inflorescences at Manuel  Monge  municipality,  Yaracuy state, Venezuela.  The disease is characterized by the presence of a grayish powdery mildew covering spikelets, which turn reddish and fail to produce seeds due to malformation of their internal structures. On PDA, the isolates presented characteristic concentric dark yellow pigmentation. Observations of sporulated mycelium from isolated colonies allowed to evidence the presence of hyaline septate mycelium and some hyaline macroconidia with a characteristic basal foot, generally with five well-defined septa, between 31-50 μm in length and 2,5-3,5 μm width. Microconidia in chains, in abundance,  hyaline and oval-shaped without septation. A total absence of chlamydospores and formation of yellow-pigmented concentric colonies in the potato-dextrose-agar medium (PDA). It was also evaluated flower stem diameter, inflorescence length, spikelet length and a number of spikelets/inflorescence, finding significant differences among groups of plants for the first three variables, which supports the systemic nature of the pathogen detected. It was concluded that the presence of this fungus in inflorescences of switchgrass prevents the formation of seeds for natural regeneration of pasture and possible mycotoxin production could represent a threat to animal health.