RESUMEN
The high susceptibility of European grapevine cultivars to downy mildew (DM) and powdery mildew (PM) causes the intensive use of fungicides. Fungus-resistant cultivars (FRCs) with different resistance (R) loci have been bred and could play an important role in reducing plant protection treatments (PPTs). However, little information is available about the extent to which PPTs can be reduced in the field through the use of FRCs and the associated economic advantages. In this study, different strategies with reduced PPTs on FRCs were tested in field experiments. The results demonstrated that the number of PPTs can be reduced by 60 to 90%, resulting in reductions in applied copper and sulfur by 52 to 79% through the use of FRCs compared with susceptible cultivars, without affecting grape or plant health. The saving potential varied among years, depending on the type of R loci and climatic conditions. Furthermore, this study highlights that completely omitting PPTs in the cultivation of FRCs can result in PM or DM infections and possible loss of yield and fruit quality. In addition to the field experiments, a two-year observation of the performance of FRCs in commercial vineyards was undertaken, which highlighted not only the significant reduction in PPTs but also the financial savings that can be achieved through the use of FRCs.
RESUMEN
BACKGROUND: 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). 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. RESULTS: A 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. CONCLUSION: This 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.