Estimating the germination dynamics of Plasmopara viticola oospores using hydro‐thermal time

Abstract

The effects of environmental conditions on the variability in germination dynamics of Plasmopara viticola oospores were studied from 1999 to 2003. The germination course was determined indirectly as the relative infection incidence (RII) occurring on grape leaf discs kept in contact with oospores sampled from a vineyard between March and July. The time elapsed between 1 January and the infection occurrence was expressed as physiological time, using four methods: (i) sums of daily temperatures > 8 ° C; (ii) hourly temperatures > 10 ° C; (iii) sums of hourly rates from a temperature-dependent function; or (iv) sums of these rates in hours with a rain or vapour pressure deficit ≤ 4·5 hPa (hydro-thermal time, HT). An equation of Gompertz in the form RII = exp[ − a · exp( − b · HT)] produced an accurate fit for both separate years ( R 2 = 0·97 to 0·99) and pooled data ( R 2 = 0·89), as well as a good accuracy in cross-estimating new data ( r between observed and cross-estimated data were between 0·93 and 0·99, P < 0·0001). It also accounted for a great part of the variability in oospore germination between years and both between and within sampling periods. Therefore, the equation of Gompertz (with a = 15·9 ± 2·63 and b = 0·653 ± 0·034) calculated over hydro-thermal time, a physiological time accounting for the effects of both temperature and moisture, produced a consistent modelling of the general relationships between the germination dynamics of a population of P. viticola oospores and weather conditions. It represents the relative density of the seasonal oospores that should have produced sporangia when they have experienced favourable conditions for germination.

Prediction of biological sensors appearance with ARIMA models as a tool for Integrated Pest Management protocols

“…In the case of P. viticola, the spore amount may be higher as a consequence of the larger drops generated by the impact of high raindrops during intense rainfall phenomena than in the case of small drops produced by less intense rainfall periods [23]. The optimum conditions for oospores germination occur in spring when rainfall is higher than 10mm for 1-2 consecutive days, accompanied by temperatures above 10-12 °C [12,24]. The temperature is very important for the duration of the ripening period and the germination rate, the optimum temperature range being from 20 °C -24 °C [24].…”

“…The majority are ineffective, despite the high quantity of fungicide applications performed with the aim of ensuring the quality of the grape bunches and harvest [11] without considering the environmental risks and economic losses for winegrowers [2]. In recent years, there have been many efforts to develop simulation models that enable pathogen development by mean regression models, mechanistic [12], neural networks. The aim of this study is to develop an accurate ARIMA (Autorregresive Integrated Model of Running Mean) time series model in order to forecast the U. necator and P. viticola risk period attacks in the Designation of Origin Ribeiro area which would allow a reduction in the number of pesticide treatments.…”

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

“…Studies based on DNA microsatellite analyses showed that new P. viticola genotypes continuously colonize host tissues from May until August, implying that oospore germination occurs from bud burst until the beginning of veraison (Gobbin et al 2005). Another indirect assessment of oospore germination, performed by determining their capacity to infect grape leaf discs in controlled optimal conditions (Hill 1998), revealed that oospores produce infectious macrosporangia until late June (Rossi et al 2008b). Numerous investigations, carried out by directly assessing oospore germination percentages on water agar at 20°C from November until July, suggested that macrosporangium formation persists from mid-end November until the end of May, less frequently until the middle of June and sporadically until the end of June (Toffolatti 2007).…”

Are plant pathogen populations adapted for encounter with their host? A case study of phenological synchrony between oak and an obligate fungal parasite along an altitudinal gradient

“…A better understanding of the ecological and evolutionary forces underlying host-pathogen phenological synchrony is of particular interest in the context of ongoing climate change, especially climate warming. Temperature has been shown to be a major driving factor for plant phenology (Cannell & Smith, 1983;Hanninen, 1995;Chuine & Cour, 1999) and is also likely to be important for fungal phenology (Desprez-Loustau et al, 1998;Scherm et al, 2001;Rossi et al, 2008). However, responses are likely to differ among species, which will affect phenological match between associated species (Memmott et al, 2007).…”