A Comprehensive Characterization of Ecological and Epidemiological Factors Driving Perennation of Podosphaera macularis Chasmothecia on Hop (Humulus lupulus)

Abstract

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.

Temporal population structure of rubber tree powdery mildew pathogen Erysiphe quercicola in Hainan, China

“…Sexual reproduction is also thought to contribute to the temporal maintenance of some other powdery mildew pathogens such as Erysiphe necator (Pearson & Gadoury, 1987), Podosphaera clandestina (Grove & Boal, 1991), Podosphaera aphanis (Jin et al, 2013), B. graminis f. sp. tritici (Jankovics et al, 2015) and Podosphaera macularis (Weldon et al, 2021). Some recent studies considered that rubber tree is the host of anamorphic E. quercicola (Liyanage et al, 2017;Wu et al, 2019).…”