Pathogenic variation among isolates ofPyricularia oryzaeaffecting rice, wheat, and grasses in Brazil

Rice blast caused by Pyricularia oryzae occurs on wheat under natural field conditions in Brazil. Isolates of P. oryzae collected from rice, wheat and grass weeds Digitaria sanguinalis, Rhynchelytrum roseum, Pennisetum setosum and Eleusine indica were tested for virulence to 30 rice, five wheat and one barley cultivars. All isolates from rice, wheat and grass weeds were pathogenic to the wheat cultivars and barley. However, none of the 10 wheat and seven grass isolates infected any of the 30 rice cultivars.