A comprehensive characterization of ecological and epidemiological factors driving perennation of Podosphaera macularis chasmothecia on hop (Humulus lupulus)

2021 ◽  
Author(s):  
William A Weldon ◽  
Michelle Marks ◽  
Amanda J Gevens ◽  
Kimberly Nicole D'Arcangelo ◽  
Lina Quesada-Ocampo ◽  
...  
Keyword(s):  
Disease Management ◽  
Powdery Mildew ◽  
Reproductive Strategies ◽  
Management Practices ◽  
Epidemiological Models ◽  
Early Season ◽  
Rain Events ◽  
Comprehensive Characterization ◽  
Podosphaera Macularis

Hop powdery mildew, caused by the ascomycete fungus Podosphaera macularis is a consistent threat to sustainable hop production. The pathogen utilizes two reproductive strategies for overwintering and perennation: (i) asexual vegetative hyphae on dormant buds that emerge the following season as infected shoots; and (ii) sexual ascocarps (chasmothecia), which are presumed to discharge ascospores during spring rain events. We demonstrate that P. macularis chasmothecia, in the absence of any asexual P. macularis growth forms, are a viable overwintering source capable of causing early season infection two to three orders of magnitude greater than that reported for perennation via asexual growth. Two epidemiological models were defined that describe (i) temperature-driven maturation of P. macularis chasmothecia; and (ii) ascosporic discharge in response to the duration of leaf wetness and prevailing temperatures. Podosphaera macularis ascospores were confirmed to be infectious at temperatures ranging from 5 to 20°C. The organism’s chasmothecia were also found to adhere tightly to the host tissue on which they formed, suggesting that these structures likely overwinter wherever hop tissue senesces within a hop yard. These observations suggest that existing early season disease management practices are especially crucial to controlling hop powdery mildew in the presence of P. macularis chasmothecia. Furthermore, these insights provide a baseline for the validation of weather driven models describing maturation and release of P. macularis ascospores that can eventually be incorporated into hop disease management programs.

Responding to an Introduced Pathogen: Podosphaera macularis (Hop Powdery Mildew) in the Pacific Northwest

2003 ◽  
Vol 4 (1) ◽  
pp. 21 ◽  
Author(s):  
Walter F. Mahaffee ◽  
Carla S. Thomas ◽  
William W. Turechek ◽  
Cynthia M. Ocamb ◽  
Mark E. Nelson ◽  
...  
Keyword(s):  
Powdery Mildew ◽  
Pacific Northwest ◽  
Management Practices ◽  
Risk Index ◽  
Lessons Learned ◽  
Infection Model ◽  
The Pacific ◽  
Sphaerotheca Macularis ◽  
The Cost ◽  
Podosphaera Macularis

Powdery mildew of hop (Humulus lupus L.), which is caused by Podosphaera macularis (formerly Sphaerotheca macularis) was found in the Yakima Valley, WA in 1996 and subsequently spread to the growing regions in Oregon and northern and southern Idaho. To rapidly assist growers in reducing the cost associated with the preventive fungicide program, the Gubler/Thomas grape powdery mildew risk infection model was adapted for hops. In addition, field surveys were utilized to identify other management practices that impacted disease development. Weather networks were established and utilized to deliver daily regional maps indicating the risk index. These maps were posted to the web for daily access. Lessons learned from this experience will be useful in addressing future pathogen introductions. Accepted for publication 28 March 2003. Published 13 November 2003.

Management of hop powdery mildew in the context of recent advances in pathogen ecology and population genetics

2021 ◽  
Author(s):  
William A Weldon ◽  
David H Gent ◽  
David Mark Gadoury
Keyword(s):  
Disease Management ◽  
Powdery Mildew ◽  
Pacific Northwest ◽  
Production Systems ◽  
Research Progress ◽  
Eastern United States ◽  
Epidemiological Models ◽  
Molecular Tools ◽  
The Pacific ◽  
Major Pathogens

The recent surge in the craft brewing market has renewed hop production throughout much of the Midwestern and Eastern United States (US), adding an element of locally sourced hops for use by regional breweries. All the while the Pacific Northwest US remains the stronghold of US hop production, supplying hops for breweries worldwide. As the industry has evolved, so too have the challenges associated with managing the major pathogens of hop (Humulus lupulus), especially with respect to Podosphaera macularis, the causal agent of hop powdery mildew. Uniquely virulent stains have evolved that can overcome widely deployed host resistance genotypes. Throughout the Midwestern and Eastern US, sexually reproducing populations of P. macularis reside on non-cultivated hop and threaten introduction into commercial hop yards. The disease was recently reported in Brazil, a first for hop production systems of the Southern Hemisphere. And as is the case for many pathosystems, the acceptance and availability of efficacious chemical control products is constantly changing. All of these factors combine to require disease management programs be as efficient, thorough, and precise as possible. Herein, this review aims to summarize research progress within the P. macularis pathosystem and synthesize major findings as they relate to disease management, placing special emphasis on recent work that has expanded the molecular tools available to study P. macularis population structure, epidemiological models that describe aspects of pathogen overwintering, and improvements in our understanding of basic pathogen ecology.

scholarly journals Hop Powdery Mildew Control Through Alteration of Spring Pruning Practices

Plant Disease ◽  
2016 ◽  
Vol 100 (8) ◽  
pp. 1599-1605 ◽  
Author(s):  
Claudia Probst ◽  
Mark E. Nelson ◽  
Gary G. Grove ◽  
Megan C. Twomey ◽  
David H. Gent
Keyword(s):  
Powdery Mildew ◽  
Pacific Northwest ◽  
Low Cost ◽  
Specific Effect ◽  
Disease Development ◽  
Quality Factors ◽  
Early Season ◽  
Yield And Quality ◽  
The Pacific ◽  
Podosphaera Macularis

Podosphaera macularis, the causal agent of hop powdery mildew, is a recurrent threat to hops in the Pacific Northwest because of the potential to reduce cone yield and quality. Early-season pruning is a common practice in hop production for horticultural reasons. Studies were conducted over a 3-year period in a commercial hop yard to quantify the effect of pruning method and timing on disease development, yield, and cone quality factors. A 4-week delay in pruning reduced the incidence of leaves with powdery mildew from 46 to 10% and cones from 9 to 1%, with the specific effect being season dependent. Pruning using chemical desiccants rather than by mechanical means had similar effects on disease levels on leaves. On cones, though, chemical pruning had a small but significant reduction in the incidence of powdery mildew compared with mechanical pruning. Cone yield, levels of bittering-acids, and color were not negatively affected in any individual year or cumulatively over three seasons when pruning treatments were applied repeatedly to the same plots during the study period. Delayed pruning may offer a low-cost means of reducing both the incidence of powdery mildew and early-season fungicide inputs in certain cultivars.

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

2014 ◽  
Vol 15 (2) ◽  
pp. 55-56 ◽  
Author(s):  
Sierra N. Wolfenbarger ◽  
Emily B. Eck ◽  
David H. Gent
Keyword(s):  
Powdery Mildew ◽  
Pacific Northwest ◽  
Host Resistance ◽  
Resistant Cultivars ◽  
Virulent Strains ◽  
The Pacific ◽  
Potential Sources ◽  
Important Disease ◽  
Podosphaera Macularis

Hop powdery mildew, caused by Podosphaera macularis, is an important disease in the Pacific Northwest. Resistant cultivars of hop have been developed and have provided field immunity to the disease until virulent strains of P. macularis emerged. Due to the increase of powdery mildew on formerly resistant cultivars, studies were conducted to characterize potential sources of host resistance. Accepted for publication 5 February 2014. Published 27 March 2014.

Characterization of Podosphaera macularis Derived from the Hop Cultivar ‘Strata’ and Strata’s Resistance to Powdery Mildew in Oregon

2021 ◽  
Author(s):  
Mary Block ◽  
Michele S. Wiseman ◽  
David H. Gent
Keyword(s):  
Powdery Mildew ◽  
Disease Risk ◽  
Severe Disease ◽  
Patent Application ◽  
State University ◽  
Single Chain ◽  
Differential Cultivars ◽  
Oregon State University ◽  
Podosphaera Macularis

Powdery mildew is one of the most destructive diseases of hop. Host resistance is a most efficient means of managing the disease, but resistance may not be durable. The cultivar Strata was developed by Oregon State University, and the patent application stated the plant was resistant to powdery mildew based on initial greenhouse screening and 8 years of observations at three locations in western Oregon. In 2019, powdery mildew colonies were reported in a commercial yard of Strata near Woodburn, Oregon. Two clonal isolates of Podosphaera macularis were isolated via single-chain transfers from colonies and characterized by inoculating each of seven differential cultivars. Cultivars with Rb, R3, and R5 were susceptible to the isolates. The susceptibility of Strata to powdery mildew was characterized by inoculating seven isolates of P. macularis with known virulences onto leaves of Strata. Sporulation appeared on Strata leaves with all of the differential isolates independent of their specific virulence, but only at trace levels with isolates possessing V6-virulence. Strata-derived isolates were phenotypically indistinguishable from Cascade-adapted isolates when inoculated onto the cultivars Cascade, Strata, and Symphony, as only Strata-derived and Cascade-adapted isolates could cause severe disease on Cascade and Strata. Like Cascade-adapted isolates, Strata-derived isolates also lack virulence on hop plants possessing the R-gene R6. These findings should inform both disease risk assessment in the field and future breeding tactics and strategies involving Strata. Further characterization of Strata is warranted to determine if its resistance is under the same genetic control as Cascade.

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