USTILAGO SPP PATHOGENIC ON AEGILOPS .3. USTILAGO-PHRYGICA, WITH A DESCRIPTIVE KEY TO ALL 3 USTILAGO SPP ON AEGILOPS

Examination of herbarium specimens, studies of biology and host range, and interspecific hybridization showed that Ustilago hordei-criniti, Ustilago tuberculata, and Ustilago mesatlantica are conspecific with Ustilago phrygica. Within this species there are strains that are specialized either on Taeniatherum caput-medusae or on one or more of the Aegilops species Aegilops cylindrica, Aegilops tauschii, and Aegilops triuncialis; on these hosts there is specialization on the species level. Other hosts are species of Agropyron, Elymus, and Hordeum. Optimum temperature for spore germination is approximately 30-degrees-C; ellipsoidal monokaryotic haploid sporidia are produced by each cell on the stout, four-celled promycelium. A brownish pink pigment diffuses into the medium if potato dextrose agar is used to culture sporidial isolates. The species has the same bipolar mating alleles as, and is thus compatible with, nine other graminicolous Ustilago spp. Infection of the host occurs through the coleoptiles of very young seedlings. The strains specialized on Aegilops pose no threat to cultivated wheat. To help identify future collections of any of the three Ustilago spp. on Aegilops, their key characteristics are summarized.