The resistance of barley to Pyricularia oryzae isolates is controlled by the Rmo2 locus irrespective of their original hosts. The resistance of barley cultivar H.E.S.4 to isolate tO-7 of P. pennisetigena (a cryptic species in the P. oryzae/grisea species complex) cosegregated with the resistance to P. oryzae isolate GFSI-1-7-2 controlled by Rmo2.a. On the other hand, its resistance to isolate NI919, belonging to another cryptic species of Pyricularia, was controlled by another gene inherited independently from Rmo2.a. These results suggest that gene-for-gene interactions underlie the resistance of barley to cryptic species of Pyricularia.