Diversity in genetic and downy mildew resistance among wild and mutagenized hops as revealed by single nucleotide polymorphisms and disease rating

Studies on wild and landrace hops from the Canadian Maritimes are scarce. This study was undertaken to broaden the genetic base of hops and to assess the reaction of the generated variants to downy mildew (DM) disease. A landrace hop (PE Royalty (P-RL)) and a commercial cultivar (Alpharoma) were mutagenized using ethylmethane sulphonate (EMS), and single nucleotide polymorphism (SNP) variations were determined using an amplicon sequencing genetic diversity study. A subset of wild types and a subset of mutagenized hops were inoculated with DM spores and rated for disease symptoms in a controlled environment. The data showed large EMS-induced genetic diversity in the target genes along with natural variations in the wild types. A diversity in DM resistance within the studied collection was also observed. The study showed DM tolerance in some P-RL landrace seedlings, suggesting that these P-RL landraces must have acquired and developed adaptation mechanisms to co-evolve with DM disease in the environment. Further, EMS-induced mutagenesis increased allelic variations that contributed to increased DM resistance in some seedlings. The data recommend the use of true hop seeds for increased genetic variability in breeding programs.