Funded by state funds and co-financed by the European Regional Development Fund (ERDF) as part of the INTERREG V Oberrhein Vitifutur program.
This project was carried out as part of a doctoral thesis by Birgit Eisenmann from October 2015 to February 2019.
The biotrophic pathogen Plasmopara viticola causes grapevine downy mildew, one of the most prevalent grapevine diseases worldwide, leading to significant reductions in berry yield and quality. Due to the lack of genetic resistance of Vitis vinifera species to downy mildew infection, wine production is heavily dependent on the use of fungicides to control this disease. To reduce the dependence of viticulture on chemical inputs, and thereby reduce the ecological and economic burden of wine production, a number of breeding programs have introgressed resistance loci from wild North American and Asian Vitis species into V. vinifera resulting in new downy mildew resistant grapevine cultivars. Despite economic and ecological advantages of fungus-resistant cultivars, they only account for around 2.4 % of the German vineyard area. A major problem, responsible for this limited use is the lack of information regarding the adapted plant protection of these new cultivars. In order to provide better information on the necessary crop protection and the fungicide saving potential of two fungus-resistant cultivars (an Rpv3 and an Rpv3/12 cultivar), field experiments were conducted. Results obtained from these experiments show that a fungicide reduction of 50 % to 75 % without negative effects on quality or quantity is possible, depending on weather conditions, grapevine development and resistance loci. Moreover, it was demonstrated that the abandonment of plant protection treatments can have severe effects on yield, quality and plant health.
Understanding the resistance mechanisms mediated by different resistance loci is essential for modern breeding strategies, as the combination of different resistance mechanisms in new grapevine cultivars could reduce the likelihood of the breakdown of resistance by the pathogen. To gain more information about the Rpv3 and Rpv12-mediated resistance mechanisms, comparative microscopic, metabolomic and transcriptomic analyses were conducted. The Rpv3-mediated defense was analyzed in more detail with a new approach that was applied in this study. It consisted of the examination of a successful and unsuccessful defense response in an Rpv3-genotype by inoculation with an Rpv3 avirulent or virulent P. viticola isolate, respectively (Fig. 1). Since there is no fast and routine way to create grapevine mutants, this approach provided a new way to gain further insight into Rpv3-mediated grapevine defense against P. viticola.
Result obtained during this work indicate that Rpv3- and Rpv12-mediated resistance is achieved by two different mechanisms. Rpv12-mediated defense seems to act faster and more effectively compared to Rpv3-mediated defense, resulting in an earlier cell death detected 8 hours post inoculation (hpi), and a strong growth inhibition that mainly arrest pathogen development within 24 hpi. The successful defense in an Rpv3 genotype is associated with cell death detected 24-32 hpi and the synthesis of fungi-toxic stilbenes, resulting in a partial resistance with reduced but not completely suppressed P. viticola growth and development.
To date, only two resistance genes are described in grapevine which are involved in recognizing pathogenic structures. To identify new genes involved in Rpv3-mediated resistance, an RNA-sequencing experiment was performed. Functional annotation of the encoded protein sequence of genes significantly upregulated during the Rpv3-mediated defense response revealed putative roles in downstream Rpv3-resistance mechanism after pathogen recognition.
Figure 1. Sporulation of virulent and avirulent Plasmopara viticola isolates on susceptible and fungus-resistant genotypes. Leaf discs of the Rpv3-1 locus containing grapevine genotypes (A, F) Cabernet Blanc and (B, G) Regent, the Rpv3-1 and Rpv3-2 loci containing grapevine genotype (C, H) Calardis Blanc, the Rpv3/12 genotype (D, I) VB Cal6-04 and the susceptible grapevine genotype (E, J) Müller-Thurgau were inoculated with the avirulent (avrRpv3+) (top) and virulent (avrRpv3¯) (bottom) P. viticola isolates. Pictures of representative leaf discs were taken at 6 days post inoculation (dpi). (K) Sporulation of P. viticola isolates on leaf discs. Sporangia were counted 6 dpi. Bars represent the average of three independent experiments with four replicates (plants) and 40 evaluated leaf discs each. Error bars show standard deviation. Means with different letters (a, b, c) are significantly different (p< 0.05).
Eisenmann et al. (2019): Rpv3–1 mediated resistance to grapevine downy mildew is associated with specific host transcriptional responses and the accumulation of stilbenes. In: BMC Plant Biology 19
Eisenmann Birgit (2019): Grapevine defense responses in Rpv3- and Rpv12-dependent resistance against Plasmopara viticola and their implication for crop protection management. Dissertation
Eisenmann (2018): Fungizide einsparen. In: Der Deutsche Weinbau
Eisenmann, Kortekamp und Bogs (2017): Widerstandskämpfer gegen Mehltau.