Abstract
BackgroundThe high susceptibility of European grapevine cultivars (Vitis vinifera) to downy mildew (Plasmopara viticola) leads to the intensive use of fungicides in viticulture. To reduce this input, breeding programs have introgressed resistance loci from wild Vitis species into V. vinifera, resulting in new fungus-resistant grapevine cultivars (FRC). However, little is known about how these different resistance loci confer resistance and what the potential reduction in fungicide applications are likely to be if these FRCs are deployed. To ensure a durable and sustainable resistance management and breeding, detailed knowledge about the different defense mechanisms mediated by the respective Rpv (Resistance to P. viticola) resistance loci is essential.ResultsA comparison of the resistance mechanisms mediated by the Rpv3–1, Rpv10 and/or Rpv12-loci revealed an early onset of programmed cell death (PCD) at 8 hours post infection (hpi) in Rpv12-cultivars and 12 hpi in Rpv10-cultivars, whereas cell death was delayed in Rpv3-cultivars and was not observed until 28 hpi. These temporal differences correlated with an increase in the trans-resveratrol level and the formation of hydrogen peroxide shortly before onset of PCD. The differences in timing of onset of Rpv-loci specific defense reactions following downy mildew infection could be responsible for the observed differences in hyphal growth, sporulation and cultivar-specific susceptibility to this pathogen in the vineyard. Hereby, Rpv3- and Rpv12/Rpv3-cultivars showed a potential for a significant reduction of fungicide applications, depending on the annual P. viticola infection pressure and the Rpv-loci. Furthermore, we report on the discovery of a new P. viticola isolate that is able to overcome both Rpv3- and Rpv12-mediated resistance.ConclusionThis study reveals that differences in the timing of the defense reaction mediated by the Rpv3-, Rpv10- and Rpv12-loci, result in different degrees of natural resistance to downy mildew in field. Vineyard trials demonstrate that Rpv12/Rpv3- and Rpv3-cultivars are a powerful tool to reduce the dependence of grape production on fungicide applications. Furthermore, this study indicates the importance of sustainable breeding and plant protection strategies based on resistant grapevine cultivars to reduce the risk of new P. viticola isolates that are able to overcome the respective resistance mechanism.
Highlights
The high susceptibility of European grapevine cultivars (Vitis vinifera) to downy mildew (Plasmopara viticola) leads to the intensive use of fungicides in viticulture
Evaluation of downy mildew resistance conferred by different Resistance to Plasmopara viticola (Rpv)‐loci To compare the level of resistance conferred by different Rpv-loci against P. viticola, susceptible grapevine cultivars i.e. ‘Müller-Thurgau’ and ‘Riesling’ and grapevine cultivars with different Rpv-loci i.e. ‘Cabernet Blanc’ and ‘Regent’ (Rpv3), ‘Merlot Khorus’ and ‘Fleurtai’ (Rpv12), ‘Soreli’ and ‘Sauvignac’ (Rpv12/Rpv3) and ‘Muscaris’ (Rpv10) were inoculated with the P. viticola
Even though P. viticola sporulation was strongly reduced in all resistant cultivars, significant differences in the degree of resistance were observed with the Rpv3-cultivars showing sporulation levels of ~ 2500–4000 sporangia ml− 1 compared to cultivars, containing Rpv10, Rpv12- or Rpv12/Rpv3-loci showing sporulation levels of less than 1000 sporangia ml− 1 (Fig. 1A; B)
Summary
The high susceptibility of European grapevine cultivars (Vitis vinifera) to downy mildew (Plasmopara viticola) leads to the intensive use of fungicides in viticulture To reduce this input, breeding programs have introgressed resistance loci from wild Vitis species into V. vinifera, resulting in new fungus-resistant grapevine cultivars (FRC). Viticulture is heavily dependent on the use of fungicides to prevention yield and quality losses, as demonstrated by the fact that more than 70% of the total quantity of fungicides used in Europe are applied in viticulture [4] To reduce these ecological and economic burdens on wine production, several breeding programs have successfully introgressed resistance loci from wild North American and Asian Vitis species into V. vinifera resulting in new fungus-resistant grapevine cultivars (FRC) [5, 6]. Whereas development of ETI has been linked to co-evolution of mildew strains with wild American grapevine species, the co-evolutionary history of Asian wild grapevine species and mildew pathogens is still not completely understood [24,25,26]
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