Next-generation sequencing reveals phylogenetic context of a powdery mildew isolate infecting wild Hordeum species and North American prairie grasses

Blumeria is a genus of powdery mildew fungi that infects cereals and wild grasses. A recent taxonomic revision separated the formerly monotypic Blumeria graminis, comprised of distinct formae speciales, into distinct species due to their reproductive isolation. Each species is specialized for infecting a specific range of grass hosts. Here, we describe an isolate of Blumeria (22-MN-GH), originally isolated from Hordeum jubatum (foxtail barley), that infects 12 other members of the tertiary gene pool of Hordeum, but not those in the primary (H. vulgare subsp. vulgare and H. vulgare subsp. spontaneum) and secondary gene pools (H. bulbosum). Based on host range and internal transcribed spacer (18S-ITS1-5.8S-ITS2-28S) sequences, isolate 22-MN-GH was identified as Blumeria americana, reflecting its similarity to previously described isolates from wild grass species in North America. Its host range includes Canada wildrye (Elymus canadensis) and prairie cordgrass (Spartina pectinata) in addition to the 13 Hordeum species in the tertiary gene pool. Based on whole genome Illumina sequencing, isolate 22-MN-GH of B. americana is genetically distinct from B. graminis, B. dactylidis, B. hordei, B. avenae, and B. graminicola. This study demonstrates the power of next generation sequencing in defining and delineating species within complex fungal genera like Blumeria.