Open Access
Issue
BIO Web Conf.
Volume 13, 2019
CO.NA.VI. 2018 - 7° Convegno Nazionale di Viticoltura
Article Number 01002
Number of page(s) 4
Section Genetic Improvements and “Omic” Analyses
DOI https://doi.org/10.1051/bioconf/20191301002
Published online 01 April 2019

© The Authors, published by EDP Sciences, 2019

Licence Creative Commons
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1 Introduction

Downy mildew (DM) and powdery mildew (PM) are the two most important plagues affecting viticulture. The first disease is caused by the oomycete Plasmopara viticola (Berl. & De Toni), while the second one by the ascomycete Erysiphe necator (Schwein.). Both reduce fruit quality and yield, either by direct infection of berries or as a negative result caused by leaf infections [1,2]. Their control is based on the massive use of fungicides, leading to problems such as environmental pollution and pathogen resistance development. The use of grapevine varieties showing durable resistance to DM and PM is a promising strategy. Unlike in almost all of Vitis vinifera varieties, sources of genetic resistance against P. viticola and E. necator were identified in a range of American and Asian wild Vitis species and used in inter-specific breeding programs through back-crossing to obtain resistant genotypes with acceptable quality features and considerable mildew resistance characteristics [3]. In an Old World country such as Italy, the demand for innovation has historically been addressed to increase the complexity of wines. However, during the last decade the need for new varieties with vinifera-like qualitative content and (mid-)resistance to pathogens has emerged among grapevine growers, nursery workers, and end-users. In order to accelerate the process of selection of resistant genotypes, one must consider genetics and genomics. In particular, given parent lines of the donors of resistance sources, the Marker-Assisted Selection (MAS) approach is based on the tracking of resistance loci (R-loci) that contain genes associated with the resistance to pathogens [4].

The program of genetic improvement for resistance to biotic stresses, which began at the Edmund Mach Foundation (FEM) in 2010, has two objectives: the first is to develop new pathogen resistant varieties, with a high level of quality, that are ready for placing on the market, while the second is to develop resistance super-donors that then act as more efficient parents for future breeding programs, releasing the resistance trait(s) to all the progeny. Hereafter, the second FEM optimized Marker-Assisted Breeding (MAB) strategy is described.

2 Materials and methods

2.1 Genetic material

Parental lines. A total of 264 grapevine accessions were studied. They included 220 non-vinifera accessions acquired from (non-)European breeding programs, an Italian private breeding platform, wild-collected samples in north-eastern America during 2011, and 44 V. vinifera varieties. Most were phenotyped for DM and PM resistance, while all were genetically characterized. Progenies. During the last 6 years a total of 86 different crossing combinations (V. hybrid × V. hybrid) were performed aiming at pyramiding R-loci. A total of 8793 progeny individuals were submitted to the MAS workflow, namely first by disease resistance screening and second by R-loci characterization.

2.2 Phenotypic screening

Parental lines. Within the experimental genetic material, 100 accessions physically available at FEM were evaluated for their degree of resistance against DM and PM, through in vitro leaf disc bioassays and in vivo pathogen inoculation on potted plants respectively. DM symptom annotation was performed based on three parameters: Severity (percentage of the disc area showing symptoms of sporulation), Incidence (number of discs with sporulation/total number of discs), according to OEPP/EPPO [5], and the OIV 452-1 descriptor [8]. PM symptoms were evaluated based on the foliar OIV 455 descriptor. Progenies. All progeny individuals were evaluated for their degree of resistance against downy and powdery mildew. Firstly, P. viticola spores were inoculated on potted seedlings following a well-established protocol [6]; secondly, prior to plant treatment and recovery, E. necator artificial infection was caused by naturally infected plants adjacent to the potted seedlings. The assessments were recorded respectively at 7 and 14 days post-inoculation (dpi) based on the OIV 452 and 455 descriptors.

2.3 Genotypic characterization

Parental lines. Following a detailed literature search, 11 reliable R-loci were analyzed in the entire parental sample set: i) 6 associated to PM resistance, Run1, Run2, Ren1, Ren2, Ren3, Ren9; ii) 5 associated to DM resistance, Rpv1, Rpv3, Rpv10, Rpv12, Rpv14. The applied PCR conditions were those reported in the overall literature, with some modifications [9]. Progenies. The progeny individuals maintained downstream of the phenotypic screening which performed well were finally characterized at the expected R-loci based on the parent combinations.

3 Results and discussion

Parental lines. Within the 100 physically available accessions, the in vitro evaluation demonstrated a wide phenotypic variability in terms of DM resistance. In particular, 41 accessions resulted in highly resistant material (OIV scores 7-9) and will be employed as a direct source of resistance in breeding sub-programs with the objective of releasing novel sustainable grapevine cultivars presenting good fruit/wine quality (e.g. good yield, absence of off-flavours). Regarding PM, only 18 out of the 100 in vivo tested accessions resulted in resistant materials. This demonstrates that PM resistance is rarer than DM resistance and highlights the importance of discovering new genetic sources. Among these accessions, a deep phenotypic characterization has recently been reported for 28 resistant varieties [7].

The following genetic study allowed the identification of already pyramided parents obtained in the past by traditional breeding activities. Moreover, most genotypes were found with no presence of any of the 11 reliable and actually analysable R-loci, representing potentially novel and exclusive genetic resources (Fig. 1).

Progenies. Out of the total 8793 plants subjected to DM and PM resistance screening, 6182 were eliminate due to their high susceptibility level to both disease while 2611 (29.7%) were maintained in order to perform the R-loci characterization. Table 1 shows the specific classes, based on the OIV scores (1-9), into which the progeny individuals maintainedwere classified.

Out of the 2611 progeny individuals retained subsequent to the phenotypic screening, 963 plants showing the highest degree of resistance and the best agronomic performance were subjected to the genotyping analysis in order to define both the number and the typology of R-loci. Besides 11.1% of genotypes carrying a single R-locus associated to DM or PM resistance, our findings highlighted the pyramidization of R-loci against DM in 48.4% and against PM in 59.5% of the analysed progeny individuals. In particular, 30.3% of genotypes showed to be pyramided for R-loci to both mildews. Overall, the most abundant class (30.9%) was represented by genotypes carrying 3 R-loci, while a maximum level of pyramiding with 7 R-loci was reached in 0.3% of cases (Fig. 2).

thumbnail Fig. 1

Rpv (A) and Run/Ren (B) loci distribution in the overall parental genetic material.

Table 1

Efficiency of the phenotypic screening for DM and PM resistance in progenies derived from V. hybrid × V. hybrid during 2013, 2014, 2015 and 2017.

thumbnail Fig. 2

Level of R-loci pyramiding in the analyzed progeny individuals.

4 Conclusions

The present survey allowed the identification of already pyramided parents obtained in the past by traditional breeding activities; this supports the role that genetics, coupled with genomics, plays in assisting genetic improvement for resistance. Moreover, novel and exclusive genetic resources were identified, providing peculiar and preparatory information for ongoing and forthcoming Marker-Assisted (pre-)Breeding programs. Following a MAS workflow, nowadays a relevant level of Rpv and Run/Ren loci pyramiding has been reached in the obtained selections. In the next coming few years, FEM is going to launch eight new varieties − carrying from 1 to 3 R-loci − which are at least mid-resistant to DM and PM.

The authors are grateful to Erhard Tutzer (Innovitis, IT) for providing already known and recently developed grapevine genotypes. The authors also thank M. Stella Grando and S. Lorenzi for their initial contribution to the work.

References

All Tables

Table 1

Efficiency of the phenotypic screening for DM and PM resistance in progenies derived from V. hybrid × V. hybrid during 2013, 2014, 2015 and 2017.

All Figures

thumbnail Fig. 1

Rpv (A) and Run/Ren (B) loci distribution in the overall parental genetic material.

In the text
thumbnail Fig. 2

Level of R-loci pyramiding in the analyzed progeny individuals.

In the text

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