Registration of seven powdery mildew-resistant wild hop germplasm lines

Cultivation of common hop (Humulus lupulus L.) has increased dramatically during the past decade, with the primary growth occurring in the Pacific Northwest of the United States. A major limitation to hop production is hop powdery mildew [caused by Podosphaera macularis (Wallr.) Braun & Takam]. To date, a comprehensive evaluation of wild hop germplasm resources for resistance to hop powdery mildew has yet to be conducted. Herein, we report the first extensive powdery mildew resistance screening of 244 wild H. lupulus populations (6,732 individuals) collected from North America and Eurasia. We used an elimination screening approach by sequentially inoculating four P. macularis isolates containing virulence on all previously described R genes. We detected the presence of powdery mildew resistance to isolates representing extant pathogenic diversity in seven germplasms (UMN-PMR-002 Male [Reg. no. GP-38, PI 699936], UMN-PMR-005 [Reg. no. GP-39, PI 699937], UMN-PMR-006 Female [GP-40, PI 699938], UMN-PMR-007 Male [Reg. no. GP-41, PI 699939], UMN-PMR-008 [Reg. no. GP-042, PI 699940], UMN-PMR-010 Male [Reg. no. GP-43, OU 699941], UMN-PMR-013 Female [Reg. no. GP-44, PI 699942]). Based upon genotypic profiling, the seven germplasms were identified in H. lupulus var. lupulus originating from Eurasia. These accessions could be used to introgress broad-spectrum powdery mildew resistance in hop breeding programs worldwide.