Characterization of Resistance to Powdery Mildew in the Hop Cultivars Newport and Comet

Wolfenbarger, Sierra N; Eck, Emily B; Gent, David H.

doi:10.1094/php-br-13-0129

Cited by 12 publications

(7 citation statements)

References 3 publications

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“…R6-virulent isolates of the fungus are now broadly established in the U.S. Pacific Northwest but were not confirmed in isolates derived from the Upper Midwest or eastern United States. Although diseased leaves of cultivars identified as Newport and Nugget were received from outside of the Pacific Northwest, both of which are reported to possess R6 (Wolfenbarger et al 2014a), R6 virulence was unable to be confirmed in this work. The lack of R6 virulence in these isolates may reflect the presence of susceptible, off-type cultivars (i.e., cultivars other than Nugget or Newport) in the yards where the samples were collected because it is common for contamination of rootstock to occur in hop yards due to the crop being vegetatively propagated.…”

Section: Discussionmentioning

confidence: 61%

Distribution and Characterization of Podosphaera macularis Virulent on Hop Cultivars Possessing R6-Based Resistance to Powdery Mildew

et al. 2016

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Host resistance, both quantitative and qualitative, is the preferred long-term approach for disease management in many pathosystems, including powdery mildew of hop (Podosphaera macularis). In 2012, an epidemic of powdery mildew occurred in Washington and Idaho on previously resistant cultivars whose resistance was putatively based on the gene designated R6. In 2013, isolates capable of causing severe disease on cultivars with R6-based resistance were confirmed in Oregon and became widespread during 2014. Surveys of commercial hop yards during 2012 to 2014 documented that powdery mildew is now widespread on cultivars possessing R6 resistance in Washington and Oregon, and the incidence of disease is progressively increasing. Pathogenic fitness, race, and mating type of R6-virulent isolates were compared with isolates of P. macularis lacking R6 virulence. All isolates were positive for the mating type idiomorph MAT1-1 and were able to overcome resistance genes Rb, R3, and R5 but not R1 or R2. In addition, R6-virulent isolates were shown to infect differential cultivars reported to possess the R6 gene and also the R4 gene, although R4 has not yet been broadly deployed in the United States. R6-virulent isolates were not detected from the eastern United States during 2012 to 2015. In growth chamber studies, R6-virulent isolates of P. macularis had a significantly longer latent period and produced fewer lesions on plants with R6 as compared with plants lacking R6, indicating a fitness cost to the fungus. R6-virulent isolates also produced fewer conidia when compared with isolates lacking R6 virulence, independent of whether the isolates were grown on a plant with or without R6. Thus, it is possible that the fitness cost of R6 virulence occurs regardless of host genotype. In field studies, powdery mildew was suppressed by at least 50% on plants possessing R6 as compared with those without R6 when coinoculated with R6-virulent and avirulent isolates. R6 virulence in P. macularis appears to be race specific and, at this time, imposes a measurable fitness penalty on the fungus. Resistance genes R1 and R2 appear to remain effective against R6-virulent isolates of P. macularis in the U.S. Pacific Northwest.

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Section: Discussionmentioning

confidence: 61%

Distribution and Characterization of Podosphaera macularis Virulent on Hop Cultivars Possessing R6-Based Resistance to Powdery Mildew

et al. 2016

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“…Before 2012, PM races present in the US Pacific Northwest possessed non‐v4/v6 virulence genes, and USDA 21087M was resistant to PM (Wolfenbarger et al, 2014). Since 2012, v4/v6 PM races have prevailed, thus ensuring susceptibility of 21087M.…”

Section: Discussionmentioning

confidence: 99%

Registration of Downy Mildew–Resistant Male Hop Germplasm USDA 21087M

Henning¹,

Gent²,

Townsend

et al. 2018

J of Plant Registrations

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USDA 21087M (Reg. No. GP-36, PI 558607) male hop (Humulus lupulus L. var. lupulus) germplasm was released to the public on 6 Dec. 2011. This germplasm has been used by the USDA-ARS for hop cultivar development for several decades. Nonagency interest in this germplasm was expressed, and release of this material is considered beneicial for the US public. USDA 21087M was obtained from the former Yugoslavia by the USDA-ARS in 1974 as Selection 3/3. The deining characteristics of USDA 21087M are its high resistance to downy mildew in the US Paciic Northwest, potential resistance to non-v4/v6 strains of powdery mildew, and potential good storage ability in hop ofspring. It is expected that hop breeders will use this germplasm as a parent for development of downy mildewresistant hop cultivars. The release of USDA 21087M will give both public and private breeders new germplasm for cultivar and germplasm development.

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“…Unfortunately, the question concerning whether or not two R-genes are working in conjunction for resistance to PM is confounded by the presence of two potential R-genes (R4 and R6) loci in the same resistant parent genotype. The female parent of this cross, USDA Newport, appears to possess both R4 and R6 genes (Wolfenbarger et al 2014) for resistance to PM. Later work by Wolfenbarger et al (2016) suggests that R4 and R6 may be misclassified, the same gene, or so tightly linked that they segregate as a single group.…”

Section: Gene Identificationmentioning

confidence: 99%

Genomic analysis of powdery mildew resistance in a hop (Humulus lupulus L.) bi-parental population segregating for “R6-locus”

2019

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Genetic response in hop to fungal pathogen infection has been evaluated at the chromosomal level through QTL analyses but very little information exists on the expression of genes during infection periods. Raw GBS reads and phenotypic data from a previously published QTL analysis along with a newly assembled PacBio-derived hop reference genome were used to re-evaluate resistance to races v4/v6 of powdery mildew (PM; Podosphaera humuli). QTL analyses revealed two tightly linked regions of association on a single linkage group. The three SNP markers most tightly linked to PM resistance (found on contig 000559F) were observed downstream from a putative R-gene locus for powdery mildew resistance. This 230 kb region contained a series of seven putative R-genes surrounded by seven putative peroxidase-3 genes downstream and seven putative glucan endo-1,3-beta-glucosidase upstream and an expressed F-box domain protein. RNAseq data showed all putative R-genes along with all putative glucan endo-1,3-beta-glucosidase genes were expressed under diseased conditions, while none of the peroxidase genes were expressed. The second region contained three SNPs found on contig 002916F next to two putative R-genes. RNAseq data showed complex expression of exons contained in putative isoforms of R-genes. This preliminary information will prove valuable information for development of precise markers located either within or next to genes responsible for race v4/v6 PM resistance.

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Characterization of Resistance to Powdery Mildew in the Hop Cultivars Newport and Comet

Cited by 12 publications

References 3 publications

Distribution and Characterization of Podosphaera macularis Virulent on Hop Cultivars Possessing R6-Based Resistance to Powdery Mildew

Distribution and Characterization of Podosphaera macularis Virulent on Hop Cultivars Possessing R6-Based Resistance to Powdery Mildew

Registration of Downy Mildew–Resistant Male Hop Germplasm USDA 21087M

Genomic analysis of powdery mildew resistance in a hop (Humulus lupulus L.) bi-parental population segregating for “R6-locus”

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