Assessment of Resistance Components for Improved Phenotyping of Grapevine Varieties Resistant to Downy Mildew.

Federica Bove,Luigi Bavaresco,Tito Caffi,Vittorio Rossi

doi:10.3389/fpls.2019.01559

Federica Bove, Luigi Bavaresco + Show 2 more

Open Access

https://doi.org/10.3389/fpls.2019.01559

Copy DOI

Abstract

Grapevine varieties showing partial resistance to downy mildew, caused by Plasmopara viticola, are a promising alternative to fungicides for disease control. Resistant varieties are obtained through breeding programs aimed at incorporating Rpv loci controlling the quantitative resistance into genotypes characterized by valuable agronomic and wine quality traits by mean of crossing. Traditional phenotyping methods used in these breeding programs are mostly based on the assessment of the resistance level after artificial inoculation of leaf discs in bioassays, by using the visual score proposed in the 2nd Edition of the International Organization of Vine and Wine (OIV) Descriptor List for Grape Varieties and Vitis species (2009). In this work, the OIV score was compared with an alternative approach, not used for the grapevine-downy mildew pathosystem so far, based on the measurement of components of resistance (RCs); 15 grapevine resistant varieties were used in comparison with the susceptible variety ‘Merlot’. OIV scores were significantly correlated with P. viticola infection frequency (IFR), the latent period for the downy mildew (DM) lesions to appear (LP50), and the number of sporangia produced per lesion (SPOR), so that when the OIV score increased (i.e., the resistance level increases), IFR and SPOR decreased, while LP50 increased. The relationship was linear for LP50, monomolecular for IFR and hyperbolic for SPOR. No significant correlation was found between OIV score and DM lesion size, sporangia produced per unit area of lesion, length of infectious period, and infection efficiency of the sporangia produced on DM lesions. The correlation between OIV score and area under the disease progress curve (AUDPC) calculated by using the RCs and a simulation model was significant and fit an inverse exponential function. Based on the results of this study, the measurement of the RCs to P. viticola in grapevine varieties by means of monocyclic, leaf disc bioassays, as well as their incorporation into a model able to simulate their effect on the polycyclic development of DM epidemics in vineyards, represents an improved method for phenotyping resistance level.

Highlights

The ooomycete Plasmopara viticola originates from North America (Millardet, 1881) and is the causal agent of downy mildew (DM), one of the major diseases of Vitis vinifera L. worldwide
This paper shows a comparison between two phenotypic methods used to assess partial resistance to P. viticola in grapevine trough an in vitro bioassay with artificial inoculation of leaf discs
Leaf disc inoculation is a well-established method to obtain reliable data for assessing grape resistance to P. viticola and many studies have revealed its strong correlation with data from naturally or artificially infected plants in the field or in pots (Stein et al, 1985; Eibach et al, 1989; Staudt and Kassemeyer, 1995; Brown et al, 1999; Boso et al, 2006; Boso and Kassemeyer, 2008; Bellin et al, 2009)

Summary

Introduction

The ooomycete Plasmopara viticola originates from North America (Millardet, 1881) and is the causal agent of downy mildew (DM), one of the major diseases of Vitis vinifera L. worldwide. The use of grapevine varieties showing partial resistance to DM represents an important tool for disease control (Töpfer et al, 2011) because it is compatible with other management options and does not have negative environmental impacts. Wild grapevine species from North America and Asia, pertaining to the genera Vitis and Muscadinia, developed different mechanisms of resistance against P. viticola because of their coevolution with the pathogen (Kortekamp et al, 1997; Bellin et al, 2009; Casagrande et al, 2011; Gessler et al, 2011; Yu et al, 2012). Depending on the Rpv locus and on the host genotype (Foria et al, 2018), the resistance responses to P. viticola infection involve different mechanisms, such as a hypersensitive response (Bellin et al, 2009; Venuti et al, 2013; Zyprian et al, 2016), callose and lignin accumulation (Dai et al, 1995; Kortekamp et al, 1997; Gindro et al, 2003), synthesis of stilbene phytoalexins (Pezet et al, 2004; Gindro et al, 2006), cell necrosis (Boso and Kassemeyer, 2008; Bellin et al, 2009; Zini et al, 2015), induction of peroxidase activity (Kortekamp et al, 1998; Toffolatti et al, 2012), and accumulation of phenolic compounds in the plant tissues surrounding the infection sites (Langcake, 1981; AlonsoVillaverde et al, 2011)

Methods

Results

Conclusion