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. 2019 Jul 18;20(14):3526.
doi: 10.3390/ijms20143526.

R-Loci Arrangement Versus Downy and Powdery Mildew Resistance Level: A Vitis Hybrid Survey

Elena Zini  1 , Chiara Dolzani  2 , Marco Stefanini  2 , Verena Gratl  3 , Paola Bettinelli  1 , Daniela Nicolini  2 , Giulia Betta  2 , Cinzia Dorigatti  2 , Riccardo Velasco  2   4 , Thomas Letschka  5 , Silvia Vezzulli  6
Affiliations

R-Loci Arrangement Versus Downy and Powdery Mildew Resistance Level: A Vitis Hybrid Survey

Elena Zini et al. Int J Mol Sci. .

Abstract

For the viticulture of the future, it will be an essential prerequisite to manage grapevine diseases with fewer chemical inputs. The development and the deployment of novel mildew resistant varieties are considered one of the most promising strategies towards a sustainable viticulture. In this regard, a collection of 102 accessions derived from crossing Vitis hybrids with V. vinifera varieties was studied. In addition to the true-to-type analysis, an exhaustive genetic characterization was carried out at the 11 reliable mildew resistance (R) loci available in the literature to date. Our findings highlight the pyramiding of R-loci against downy mildew in 15.7% and against powdery mildew in 39.2% of the total accessions. The genetic analysis was coupled with a three-year evaluation of disease symptoms in an untreated field in order to assess the impact of the R-loci arrangement on the disease resistance degree at leaf and bunch level. Overall, our results strongly suggest that R-loci pyramiding does not necessarily mean to increase the overall disease resistance, but it guarantees the presence of further barriers in case of pathogens overcoming the first. Moreover, our survey allows the discovery of new mildew resistance sources useful for novel QTL identifications towards marker-assisted breeding.

Keywords: Erysiphe necator; Plasmopara viticola; disease resistance loci; grapevine; marker-assisted breeding; pyramiding.

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Conflict of interest statement

All authors declared no conflicts of interest.

Figures

Figure 1
Figure 1
Dendrogram showing the genetic distance based on cluster analysis (Neighbour Joining clustering; Euclidean similarity).
Figure 2
Figure 2
Grouped bar chart showing the percentual of accessions with single resistance locus, combination of two, three and four resistance (R) loci and absence of any studied R-locus. Rpv: Resistance to Plasmopara viticola; Run: Resistance to Uncinula necator (from Muscadinia spp.); Ren: Resistance to Erysiphe necator (from Vitis spp.).
Figure 3
Figure 3
Box plots comparing OIV scores of resistance level in years 2016, 2017 and 2018 for downy (A) and powdery (B) mildew on leaves (green) and bunches (violet). Per each year, the lowest score between evaluations was chosen.
Figure 3
Figure 3
Box plots comparing OIV scores of resistance level in years 2016, 2017 and 2018 for downy (A) and powdery (B) mildew on leaves (green) and bunches (violet). Per each year, the lowest score between evaluations was chosen.
Figure 4
Figure 4
Evaluation of field resistance to downy (A) and powdery (B) mildew on leaves (green) and bunches (violet) on clustered accessions according to the presence of resistance (R) loci. Per each accession, OIV scores were averaged by 3-years. Per each year, the lowest score between evaluations was chosen. Box plots show medians by middle line and means by x. *: p < 0.05; **: p < 0.01.
Figure 4
Figure 4
Evaluation of field resistance to downy (A) and powdery (B) mildew on leaves (green) and bunches (violet) on clustered accessions according to the presence of resistance (R) loci. Per each accession, OIV scores were averaged by 3-years. Per each year, the lowest score between evaluations was chosen. Box plots show medians by middle line and means by x. *: p < 0.05; **: p < 0.01.
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