The Study of the Germination Dynamics of Plasmopara viticola Oospores Highlights the Presence of Phenotypic Synchrony With the Host

Abstract

The plant disease onset is a complex event that occurs when the pathogen and the host encounter in a favorable environment. While the plant–pathogen interaction has been much investigated, little attention has been given to the phenological synchrony of the event, especially when both plant and pathogen overwinter, as in the case of grapevines and the downy mildew agent, the oomycete Plasmopara viticola. Oospores allow this obligate parasite to survive grapevine dormancy and, germinating, produce inoculum for primary infections. During overwintering, environmental factors influence the potential oospore germination. This study aimed at investigating the existence of synchrony between the pathogen and the host by identifying and quantifying the most important factors determining oospore maturation and germination and the relationship existing with grapevine phenology. Generalized linear models (GLM and GLMM) were used to analyze the germination dynamics of the oospores overwintered in controlled and field conditions and incubated in isothermal conditions, and oospore viability tests were carried out at different time points. Results showed that the most indicative parameter to describe the germination dynamics is the time spent by the oospores from the start of overwintering. The oospores overwintered in field showed phenological traits related to grapevine phenology not observed in controlled conditions. In particular, they completed the maturation period by the end of grapevine dormancy and germinated more rapidly at plant sprouting, when grapevine reaches susceptibility. Overall, the oospores proved to be able to modulate their behavior in close relationship with grapevine, showing a great adaptation to the host’s phenology.

Oospore germination dynamics and disease forecasting model: an integrated approach for downy mildew management

“…Interestingly, in correspondence with the infection risk indicated by the EPI model, the oospores showed a reduction in t (with minimum values ranging from two to five days). This confirms that t significantly decreases when the plant reaches susceptibility to P. viticola (Maddalena et al, 2021). It must be point out that, since the oospores are the only overwintering structures of the pathogen and the source of the vital inoculum for primary infection, obtaining real biological data on oospore germination is particularly important also from an epidemiological point of view since it provides information on the availability of inoculum for primary infections.…”

“…Relating the influence of environmental conditions to the germination dynamics could provide indication on inoculum availability for primary infections and the need for a fungicide treatment. A recent study demonstrated that the number of days required by the oospores to germinate (t) decreases when grapevine reaches susceptibility to P. viticola (Maddalena et al, 2021). The promising results obtained in the previous years led the authors to evaluate the effectiveness of EPI model extending its use in other viticultural area.…”

“…Grapevine leaves, showing downy mildew mosaic symptoms, were collected at the middle of October 2020. Twenty nylon bags containing leaf fragments rich in oospores were prepared(Maddalena et al, 2021). Germination assays were carried out once or twice a week starting from grapevine sprouting (second half of March 2021) until bunch closure (end of June 2021) as described by(Maddalena et al, 2021).…”

“…Twenty nylon bags containing leaf fragments rich in oospores were prepared(Maddalena et al, 2021). Germination assays were carried out once or twice a week starting from grapevine sprouting (second half of March 2021) until bunch closure (end of June 2021) as described by(Maddalena et al, 2021). For each nylon bag, three agar plates (technical replicates) were inoculated with four 10 l droplets of 100 oospores and incubated at the optimal temperature of 20°C.…”

Grapevine Downy Mildew Warning System Based on NB-IoT and Energy Harvesting Technology

“…The proposed model for primary infection warning starts when the grapevine shoots are in stage 13 of the BBCH scale (i.e., the shoots are at least 10 cm long, or a few unrolled leaves) at minimum [30]. Then, the average daily air temperature, precipitation, wind, and daytime/nighttime are monitored.…”