Management of Hop Powdery Mildew in the Context of Recent Advances in Pathogen Ecology and Population Genetics

Abstract

The recent surge in the craft brewing market has renewed hop production throughout much of the Midwestern and Eastern United States, adding an element of locally sourced hops for use by regional breweries. All the while, the U.S. Pacific Northwest remains the stronghold of U.S. 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, 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 United States, sexually reproducing populations of P. macularis reside on noncultivated 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. Also, 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.