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Background
Climate change will increase the occurrence of plants simultaneously suffering drought and pathogen stress. Although it is well-known that drought can alter the way plants respond to pathogens, knowledge about the effect of concurrent drought and biotic stress in grapevine is scarce. This is especially true for Plasmopara viticola, the causal agent of grapevine downy mildew. This research addresses how vines with different drought tolerance respond to the challenge with P. viticola, drought stress or their combination, and how one stress affects the other.
Results
Artificial inoculation was performed on two cultivars, exposed to full or deficit irrigation, in the Mediterranean climate of Cyprus. In parallel, leaf disks from these plants were inoculated in controlled conditions. Leaves were sampled at an early infection stage to determine the influence of the single and combined stresses on oxidative parameters, chlorophyll, and phytohormones. Under irrigation, the local Cypriot cultivar Xynisteri was more susceptible to P. viticola than the drought-sensitive Chardonnay. The successful infection by P. viticola at 1.5 days post inoculation was associated with high levels of indole-3-acetic acid (IAA), salicylic acid (SA), jasmonic acid (JA), and proline and strong decreases in antioxidant enzyme activity. Drought, on the other hand, triggered the accumulation of IAA and abscisic acid (ABA), which antagonized JA and SA. Exposure to drought stress increased the susceptibility to P. viticola of the leaves inoculated in controlled conditions. Conversely, both cultivars showed resistance against P. viticola when inoculated in planta under continued deficit irrigation. Despite their resistance, the pathogen-associated responses in IAA, antioxidant enzyme activity, and proline still occurred in these drought-stressed plants. Surprisingly, abscisic acid, rather than the generally implicated jasmonic and salicylic acid, seemed to play a prominent role in this resistance.
Conclusions
Drought exposure increased the susceptibility of in vitro inoculated leaves. Conversely, deficit irrigation induced resistance to P. viticola in both Chardonnay and Xynisteri when inoculated in planta. ABA, rather than JA and SA, was implicated in this resistance. The irrigation-dependent susceptibility highlights that the changing climate and the practices used to mitigate its effects, may have a profound impact on plant pathogens.
Keywords
Climate change, irrigation, drought stress, biotic stress, grapevine, downy mildew, Plasmopara viticola, phytohormones, oxidative stress, abscisic acid
Figure 1
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Figure 7
This is a list of supplementary files associated with this preprint. Click to download.
- Additionalfile1.xlsx
Additional file 1 (.xls): Table S1 P-values for the single drought stress and single pathogen stress. Significant differences (p<0.05) are highlighted in green. This analysis was performed on subsets of the data, in order to exclude interactions. For the effect of single drought stress, fully irrigated and deficit irrigated, water-inoculated plants were compared (control treatments of the continued exposure to full/deficit irrigation – see Fig. 1). For the effect of single pathogen stress, water-inoculated and pathogen-inoculated, fully irrigated plants were compared (continued exposure to full irrigation – see Fig. 1).
- Additionalfile21.tif
Additional file 2 (.tif): Fig. S1 Effect of drought stress on the dynamics of the plants’ physiological parameters. Stomatal conductance, SPAD, and chlorophyll fluorescence were measured in Xynisteri (XYN) and Chardonnay (CHAR) plants subjected to full (FI) or deficit (DI) irrigation without pathogen treatment (previous or continued exposure to full/deficit irrigation, before inoculation – see Fig. 1). The bars and error bars show the mean and the standard deviation, respectively. No significant differences were observed between cultivars. The significant differences between the irrigation regimes are indicated with an asterisk at the corresponding time point (Mann-Whitney U-test; p<0.05). No statistics were performed on the stomatal conductance at 14 dot since this was, exceptionally, measured for only two deficit irrigated plants.
- Additionalfile3.xlsx
Additional file 3 (.xls): Table S2 P-values for the different factors and interactions, retained in the models after model selection. Interaction terms that were not important for the models, were removed based on the AIC. The linear regression analyzes the interactions between the predictor variables: cultivar (Chardonnay or Xynisteri), irrigation (full or deficit), duration (of the irrigation treatment; 9 or 16 dot), and pathogen (P. viticola or water inoculation). Highlighted cells have p-value < 5% (dark green); 5%< p-value <10% (light green); 10%<p-value<15% (grey).
- Additionalfile4.xlsx
Additional file 4 (.xls): Table S3 Coefficient estimates for the different factors and interactions, retained in the models after model selection. Interaction terms that were not important for the models, were removed based on the AIC. The linear regression analyzes the interactions between the predictor variables: cultivar (Chardonnay or Xynisteri), irrigation (full or deficit), duration (of the irrigation treatment; 9 or 16 dot), and pathogen (P. viticola or water inoculation). Coefficients with p-value < 15% are highlighted, in a darker shade if p-value<5%. The colors indicate a positive (blue) or negative (red) correlation.
- Additionalfile51.tif
Additional file 5 (.tif): Fig. S2 Relative humidity and temperature during the experiment. Data were recorded every 20 minutes with an on-site data logger in sheltered conditions.
- Additionalfile61.tif
Additional file 6 (.tif): Fig. S3 Volumetric water content (VWC) of the soil during the experiment. The deficit irrigation (DI) was maintained at 40% of the full irrigation (FI) based on the volumetric pot soil water content. The VWC was measured daily following the water application. The full line indicates the average VWC of 8 pots at each time point. The bands illustrate the 95% confidence intervals.
- Additionalfile7.xlsx
Additional file 7 (.xls): Table S4 Main data supporting the results of this article
- ESM1.pdf
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This is a preprint, a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Research article
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This manuscript passed our Prescreen assessment
Complete author information
Appropriate declaration statements
Potential risks to human health
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History
CURRENT STATUS: Posted
The most recent version of this article is available here.
No community comments so far
Version 2
Posted 12 Nov, 2020
No comments provided
No comments provided
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License:
This work is licensed under a CC BY 4.0 License. Read Full License
The most recent version of this article is available here.
Background
Climate change will increase the occurrence of plants simultaneously suffering drought and pathogen stress. Although it is well-known that drought can alter the way plants respond to pathogens, knowledge about the effect of concurrent drought and biotic stress in grapevine is scarce. This is especially true for Plasmopara viticola, the causal agent of grapevine downy mildew. This research addresses how vines with different drought tolerance respond to the challenge with P. viticola, drought stress or their combination, and how one stress affects the other.
Results
Artificial inoculation was performed on two cultivars, exposed to full or deficit irrigation, in the Mediterranean climate of Cyprus. In parallel, leaf disks from these plants were inoculated in controlled conditions. Leaves were sampled at an early infection stage to determine the influence of the single and combined stresses on oxidative parameters, chlorophyll, and phytohormones. Under irrigation, the local Cypriot cultivar Xynisteri was more susceptible to P. viticola than the drought-sensitive Chardonnay. The successful infection by P. viticola at 1.5 days post inoculation was associated with high levels of indole-3-acetic acid (IAA), salicylic acid (SA), jasmonic acid (JA), and proline and strong decreases in antioxidant enzyme activity. Drought, on the other hand, triggered the accumulation of IAA and abscisic acid (ABA), which antagonized JA and SA. Exposure to drought stress increased the susceptibility to P. viticola of the leaves inoculated in controlled conditions. Conversely, both cultivars showed resistance against P. viticola when inoculated in planta under continued deficit irrigation. Despite their resistance, the pathogen-associated responses in IAA, antioxidant enzyme activity, and proline still occurred in these drought-stressed plants. Surprisingly, abscisic acid, rather than the generally implicated jasmonic and salicylic acid, seemed to play a prominent role in this resistance.
Conclusions
Drought exposure increased the susceptibility of in vitro inoculated leaves. Conversely, deficit irrigation induced resistance to P. viticola in both Chardonnay and Xynisteri when inoculated in planta. ABA, rather than JA and SA, was implicated in this resistance. The irrigation-dependent susceptibility highlights that the changing climate and the practices used to mitigate its effects, may have a profound impact on plant pathogens.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
This is a list of supplementary files associated with this preprint. Click to download.
- Additionalfile1.xlsx
Additional file 1 (.xls): Table S1 P-values for the single drought stress and single pathogen stress. Significant differences (p<0.05) are highlighted in green. This analysis was performed on subsets of the data, in order to exclude interactions. For the effect of single drought stress, fully irrigated and deficit irrigated, water-inoculated plants were compared (control treatments of the continued exposure to full/deficit irrigation – see Fig. 1). For the effect of single pathogen stress, water-inoculated and pathogen-inoculated, fully irrigated plants were compared (continued exposure to full irrigation – see Fig. 1).
- Additionalfile21.tif
Additional file 2 (.tif): Fig. S1 Effect of drought stress on the dynamics of the plants’ physiological parameters. Stomatal conductance, SPAD, and chlorophyll fluorescence were measured in Xynisteri (XYN) and Chardonnay (CHAR) plants subjected to full (FI) or deficit (DI) irrigation without pathogen treatment (previous or continued exposure to full/deficit irrigation, before inoculation – see Fig. 1). The bars and error bars show the mean and the standard deviation, respectively. No significant differences were observed between cultivars. The significant differences between the irrigation regimes are indicated with an asterisk at the corresponding time point (Mann-Whitney U-test; p<0.05). No statistics were performed on the stomatal conductance at 14 dot since this was, exceptionally, measured for only two deficit irrigated plants.
- Additionalfile3.xlsx
Additional file 3 (.xls): Table S2 P-values for the different factors and interactions, retained in the models after model selection. Interaction terms that were not important for the models, were removed based on the AIC. The linear regression analyzes the interactions between the predictor variables: cultivar (Chardonnay or Xynisteri), irrigation (full or deficit), duration (of the irrigation treatment; 9 or 16 dot), and pathogen (P. viticola or water inoculation). Highlighted cells have p-value < 5% (dark green); 5%< p-value <10% (light green); 10%<p-value<15% (grey).
- Additionalfile4.xlsx
Additional file 4 (.xls): Table S3 Coefficient estimates for the different factors and interactions, retained in the models after model selection. Interaction terms that were not important for the models, were removed based on the AIC. The linear regression analyzes the interactions between the predictor variables: cultivar (Chardonnay or Xynisteri), irrigation (full or deficit), duration (of the irrigation treatment; 9 or 16 dot), and pathogen (P. viticola or water inoculation). Coefficients with p-value < 15% are highlighted, in a darker shade if p-value<5%. The colors indicate a positive (blue) or negative (red) correlation.
- Additionalfile51.tif
Additional file 5 (.tif): Fig. S2 Relative humidity and temperature during the experiment. Data were recorded every 20 minutes with an on-site data logger in sheltered conditions.
- Additionalfile61.tif
Additional file 6 (.tif): Fig. S3 Volumetric water content (VWC) of the soil during the experiment. The deficit irrigation (DI) was maintained at 40% of the full irrigation (FI) based on the volumetric pot soil water content. The VWC was measured daily following the water application. The full line indicates the average VWC of 8 pots at each time point. The bands illustrate the 95% confidence intervals.
- Additionalfile7.xlsx
Additional file 7 (.xls): Table S4 Main data supporting the results of this article
- ESM1.pdf
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