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Effect of Environmental Conditions and Phenology in the Dispersal of Secondary Erysiphe Necator Conidia in a Vineyard

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Effect of Environmental Conditions and Phenology in the Dispersal of Secondary Erysiphe Necator Conidia in a Vineyard Vitis 58 (Special Issue), 49–58 (2019) DOI: 10.5073/vitis.2019.58.special-issue.49-58 Effect of environmental conditions and phenology in the dispersal of secondary Erysiphe necator conidia in a vineyard E. GONZÁLEZ-FERNÁNDEZ1), A. PIÑA-REY1), M. FERNÁNDEZ-GONZÁLEZ1), 2) and F. J. RODRÍGUEZ-RAJO1) 1) CITACA, Agri-Food Research and Transfer Cluster, Sciences Faculty, University of Vigo, Ourense, Spain 2) Earth Sciences Institute (ICT), Pole of the Faculty of Sciences University of Porto, Porto, Portugal Summary ades, we are witnessing a huge agriculture mechanization and a rapid modernization of the European viticulture sector An integrated powdery mildew management strat- because of investments in this primary economical area. egy to identify the principal moments of secondary The biggest vineyard surface at world level was placed in Erysiphe necator conidia dispersal in a vineyard based Spain (13 %) been the third largest wine producer country on aerobiological, phenological and meteorological data (13 %) just below Italy (18 %) and France (17 %) (Mapama was developed. An adaptation of the physiological P-days 2016). Diseases and pests of crops affect potential yields and model was conducted to obtain a descriptive equation economic profits. A co-evolution of plants and their parasitic for the prediction of the advantageous meteorological fungi was detected, which explains their fitted adaptation conditions for Erysiphe necator conidia dispersal in the to the real changing conditions of the vineyard agrosystem. vineyards of the Ribeiro Designation of Origin area. The specific bioclimatological conditions of Northwest Moreover, a regression model was developed to predict Spain favour the development of fungal phytopathogenic the conidia concentration as a function of the weather diseases, which are responsible for remarkable annual yield and aerobiological variables with the highest influence loss. Powdery mildew, caused by Erysiphe necator is one of on airborne E. necator spores. Additionally, phenological the main harmful grapevine diseases in most growing areas observations were conducted during the vegetative cycle of the world (BOIS et al. 2017). of Vitis vinifera, with the aim to identify the most suscep- E. necator belongs to the Erysiphaceae family, being tible phenological stages to powdery mildew infection an obligate vine parasitic ascomycetous fungi with a bipo- by relating them with the detected atmospheric spore lar-heterothallic mating system (EVANS et al. 1997). The concentrations. The study was carried out from 2008 to disease cycle of this fungus is based on two main sources of 2018 in an experimental vineyard. The E. necator spores primary inoculum, which are the mycelium within dormant were trapped using a Lanzoni VPPS-2000 sampler and buds and the ascospores released by cleistothecia (HALLEEN the phenological observations were conducted following and HOLZ 2001). In areas with mild winters, dormant infected the BBCH standardized scale. The highest total fungal lateral buds cause flag shoots in the following spring (HILL spore amount per season in the atmosphere of the vine- 1990). But in colder viticultural regions flag shoots are not yard was detected in 2013 with 4828 spores m-3, while the produced, what had been attributed to the reduced winter lowest amount was recorded in 2009 with 883 spores m-3. hardiness of the infected lateral buds (GADOURY et al. 2012). In general, the highest daily airborne spore concentra- The weakening and mortality of hyphal tissues within the tions were detected during the Flowering (stage 6) or in active colonies under low temperatures was demonstrated the previous and next stages, whereas the maximum total for nascent colonies on leaves (MOYER et al. 2010). The spore amount by stage was recorded during Development overwintering cleistothecia are an additional source of of Fruits (stage 7). The proposed threshold of P-days for primary inoculum in the areas where the flag shoots are potential secondary infections in the Ribeiro D.O. ranges common (GADOURY et al. 2012). This resistance structure from 120 to 160 P-days. The combination of aerobiologi- is the result of the sexual part of the pathogen's life cycle, cal, phenological and meteorological data provides us and it implies the contact between two parent hyphae. In a useful tool for the knowledge of the Erysiphe necator very rainy areas, the emergence of the primary infection conidia dispersal behaviour bringing agricultural prac- from ascospores released by cleistothecia is the prevailing tices closer to a sustainable system. process (JARVIS et al. 2002). During late summer and autumn, mature cleistothecia are dispersed by rain to the bark of the Key words: Erysiphe necator; P-days, conidia dispersal; vine or to the soil (GADOURY and PEARSON 1988), where they grapevine; airborne spores forecast. overwinter. These structures can be dispersed as well by high winds (GROVE 2004). The optimal temperature for infection by ascospores is 20 °C to 25 °C, being significantly reduced Introduction at 15 °C or below. The thermal thresholds for ascosporic infections are 5 °C and 31 °C (JAILLOUX et al. 1998). The The wine-making sector embraces important worldwide fastest mildew colony growth and sporulation occurs from socio-cultural and environment values. During the last dec- 23 °C to 30 °C, with an optimum temperature of 26 °C (DELP Correspondence to: Dr. E. GONZÁLEZ-FERNÁNDEZ, Department of Plant Biology and Soil Sciences University of Vigo, Circunvalación ao Campus Universitario, 36310 Vigo, Pontevedra, Spain. E-mail: [email protected] © The author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution Share-Alike License (http://creative-commons.org/licenses/by-sa/4.0/). 50 E. GONZÁLEZ-FERNÁNDEZ et al. 1954). For initiation of asexual sporulation, a previous pe- treatment decisions only consider meteorological variables riod of superficial vegetative growth of mildew colonies is as high temperature conditions after rainy days. But the necessary. GADOURY et al. (2012) found that the stimulation disease events are promoted by a combination of different of conidiation in the colony comes from a quorum-sensing favourable conditions. Only a treatment application should signal from the centre of the colony. They demonstrated be necessary when both, a real risk of infection and a po- that the removal of the colony centre before signalling tentially economic damage are identified. Excessive use of nearly doubled the latent period from hyphae development phytosanitary chemicals causes serious consequences for the to sporulation. This latent period can be increased as well environment and human health (GUBLER and THOmaS 2006). by the thermal conditions, from 5 d with constant optimal One of the most important is related with the crop ecosystem temperatures to a minimum of 25 d at 9 °C and under field damage by stimulating the appearance of resistances in the conditions. Dispersal of conidia is very important in polycy- fungus or the beneficial mycological flora reduction (GUBLER clic diseases with aerial spread, such as grape powdery mil- and THOmaS 2006). Most of the Integrated Pest Management dew. This factor determines the spatio-temporal extension strategies are based on a replacement or reduction of the of epidemics (AYLOR 1990). Conidia dispersal is a passive chemical protection techniques with a more eco-friendly process triggered by weather (WILLOCQUET et al. 1998) and purpose (BARZMAN et al. 2015). crop managing factors. High-pressure sprays against other As part of these control strategies, several models grape harmful pathogens (like insects or fungal diseases) can have been developed to achieve a better phytosanitary enhance powdery mildew epidemics by conidia dispersal, as control of grape powdery mildew (BENDEK et al. 2007, the high flow rates generated induce high turbulence in the FERNÁNDEZ-GONZÁLEZ et al. 2013, ARafaT 2015, ORIOLANI canopy with shaking of infected leaves and high air speeds at et al. 2015). The airborne spore concentration is a great the sporulating powdery colonies of lesion sites (WILLOCQUET indicator of the phytochemical treatment need, as the inoc- and CLERJEAU 1998). Wind causes instantaneous dispersal ulum presence can vary within the different development of E. necator conidia, although the minimum wind speed stages of polycyclic diseases (THIESSEN et al. 2017). Some for dispersal is 2.3 m·s-1 (WILLOCQUET et al. 1998, HALLEEN of the models are focussed on primary ascosporic infection and HOLZ 2001). processes (CAFFI et al. 2011, 2012), and most of them are All green organs are susceptible to powdery mildew based on weather related variables (ARafaT 2015, ORIO- infection: sprouts, leaves, inflorescences and immature LANI et al. 2015). Among the weather-based models, the berries (FERNÁNDEZ-GONZÁLEZ et al. 2013). Infection symp- Gubler-Thomas risk index (GUBLER et al. 1999, GUBLER and toms appears as grey-white dust on both sides of leaves or THOMAS 2006) is the most widely used as epidemiological fruits (represented by superficial mycelium and conidia) and model for grapevine powdery mildew as it works with tem- diffuse dark green spots in vine shoots (BENDEK et al. 2002). perature and leaf wetness duration to predict the ascospores Split berries indicate a typical signal of disease presence, release to initiate the risk index. This model, that predicts due to parasitized epidermic dead tissue in young berries both ascosporic and secondary conidial stages of the disease, when the fruit is still growing (CARISSE et al. 2006). Skin ranges from 0 to 100 acting as an advisory tool for growers, lesions represent an important penetration point for other who can use it to adjust the fungicide timing. Moreover, it phytopathogens, such as Botrytis cinerea (CARISSE et al. was originally developed to be used in California, and has 2006, FERNÁNDEZ-GONZÁLEZ et al. 2012), since the grape been successfully adapted to other bioclimatic areas (BENDEK skin acts as an effective barrier against conidia penetration et al. 2007, FERNÁNDEZ-GONZÁLEZ et al. 2013), and even to (COERTZE et al. 2001). other crops (GROVE et al.
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