A new approach to modelling the dynamics of oospore germination in Plasmopara viticola

Abstract

Oospores, the only overwintering structures of Plasmopara viticola, the causal agent of grapevine downy mildew, are the unique source of inoculum for primary infections in vineyards. We show that their germination dynamics depend on both climatic and endogenous factors. In particular, overwintering in controlled conditions suggests that low temperatures prolong the oospore germinability, while constant or gradually alternating water availability increases germination rates. However, wide fluctuations in germination percentage, observed both in naturally overwintered oospores, and under controlled conditions, indicate an important role for endogenous factors in the germination frequency. Ad hoc experimental assays and microscopic observations highlight an important role for calcium in the germination process. However, for a profound understanding of the biological mechanisms underlying oospore germination, mathematical models of the germination dynamics are needed. But, classical differential models of germination dynamics are, with current knowledge, prohibitive due both to the complexity of the underlying processes and knowledge incompleteness. Then, we propose a hybrid method derived from the integration of qualitative differential models and fuzzy systems.

Modeling climate impact on an emerging disease, thePhytophthora alni‐induced alder decline

“…Indeed, P. alni does not produce chlamydospores, and because it is a triploid homoploid hybrid, it produces nonviable oospores (Delc an & Brasier, 2001;Husson, unpublished results). Chlamydospores are mitotic spores produced by many Phytophthora species, while oospores are the result of sexual reproduction; both are the thick-walled spores that enable Phytophthora to survive harsh conditions (Vercesi et al, 2010;Zhang et al, 2012). As a consequence of this lack of resistant spores, P. alni has been demonstrated to persist in soil for only few months in the absence of host (Jung & Blaschke, 2004;Elegbede et al, 2010), and therefore inoculum levels may be strongly affected by harsh climatic conditions.…”

A bioeconomic model of downy mildew damage on grapevine for evaluation of control strategies

“…For example, Rossi et al (2009) proposed a more detailed model for primary infections (Caffi et al, , 2011Vercesi et al (2010) suggested a modeling approach to P. viticola oospore germination dynamics that demonstrated showing the importance of both climatic and endogenous factors and Calonnec et al (2008Calonnec et al ( , 2009 precisely quantified hostepathogen relations in the case of grapevine powdery mildew. Sporulation and its decline over time can also be described in a more detailed manner than in our model; for example, Hill (1989) related the sporulation of individual lesions to the temperature over 2e3 months, and Kennelly et al (2007a) found that spore production decline was more accurately related to the number of repeated cycles of sporulation.…”

“…This last parameter characterizes the newly infected leaf area at each favorable occurrence and can be considered as an indicator of the primary infection pressure by downy mildew under given weather and crop conditions. Therefore, all primary infections produced equal areas of infected leaf, and they can occur throughout the season, as stated by Kennelly et al (2007a) and Vercesi et al (2010). At the end of latency, the hyphae grow outside the leaf surface, and produce spore-bearing organs; the spores are released into the environment and extend the infected area through secondary infections.…”

A time‐course investigation of resistance to the carboxylic acid amide mandipropamid in field populations of Plasmopara viticola treated with anti‐resistance strategies

“…In October, leaves showing downy mildew mosaic symptoms were randomly collected in the vineyards. Three samples, consisting of 50 leaf fragments rich in oospores excised under a microscope (Zeiss Primo Vert; Carl Zeiss, Milan, Italy), were prepared per plot . The samples were stored at 5 °C on a sandy substrate kept regularly watered with 300 mL of water.…”