Due to its reproducibility and sensitivity, real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) has become the method of choice for quantifying gene expression. However, the accuracy of RT-qPCR is prone to bias if proper precautions are not taken, e.g. starting with intact, non-degraded RNA, considering the PCR efficiency and using the right reference gene(s) for normalization. It has been reported that some of the well-known reference genes are differentially regulated under certain experimental conditions suggesting that there is no gene that could be used as a universal reference. This paper aims at selecting the most suitable reference gene(s) out of six putative genes to be used as normalizer(s) for quantification of gene expression in the grapevine-downy mildew interaction as well as upon induced resistance with chemical elicitors. Moreover, the paper aims at determining the optimal number of reference genes to be used in normalization, since it has been emphasized in the literature that using multiple reference genes increases accuracy. Two different software tools, geNorm and Normfinder, were used to identify the most stable reference genes in grapevine under the aforementioned conditions. The importance of the choice of adequate reference genes is highlighted by studying chitinase expression.

Inducing host plant-based systemic resistance is one of the modes of action involved in tri-trophic interactions between host plants, pests and mutualistic microorganisms. Two different types of systemic resistance – systemic acquired resistance (SAR) and induced systemic resistance (ISR) – were found to be functional against pathogens and plant-parasitic nematodes. In this study, the ability of Trichoderma harzianum isolate T10 and insecticidal active neem powder (NP) to induce systemic resistance in tomato against the root-knot nematode Meloidogyne javanica was compared with salicylic acid (SA) and jasmonic acid (JA) as standard elicitors for SAR and ISR, respectively. Results showed that, when the biotic and abiotic elicitors were applied to the inducer side of a split root plant system, a significant reduction in nematode infection was observed on the responder side. Physiological changes in the tomato plant due to the induction of SAR or ISA by these biotic and abiotic elicitors were further investigated using HPLC. Results demonstrated that T10 significantly increased the accumulation of different metabolites in the shoot of the tomato over the NP, JA and SA elicitors. Furthermore, the results demonstrated that several metabolic, physical and biochemical changes occurred in the shoots of the treated plants with both the biotic and abiotic elicitors. The percentage of membrane leakage (Ml) at nematode-infected tomato roots was significantly high, but the differences in percentage leakage were not significant in other treatments compared to the non-infested control. The best results were recorded with SA, T10 and NP, which gave the lowest MI% compared to the infested plants.

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Atmospheric carbon dioxide (CO 2 ) concentrations are among the chief factors shaping the mode and magnitude of interactions between plants and herbivorous insects. Here, we describe the first global analysis of systemic transcriptomic responses of grapevine Vitis vinifera plants to feeding of European grapevine moth Lobesia botrana larvae at future elevated CO 2 concentrations. The study was conducted on mature, fruit-bearing grapevine plants under ambient and elevated CO 2 concentrations in a grapevine free-air carbon dioxide enrichment (FACE) facility. Grapevine transcriptional response to herbivory was clearly dependent on phenological stage, with a higher number of differentially expressed genes identified at fruit development compared to berry ripening. At fruit development, more transcripts were differentially expressed as a response to herbivory under elevated compared to ambient CO 2 concentrations. Classification of the respective transcripts revealed that in particular genes involved in metabolic pathways, biosynthesis of secondary metabolites and plant-pathogen interactions were significantly enriched. Most of these genes had similar expression patterns under both CO 2 concentrations, with a higher fold-change under elevated CO 2 concentrations. Differences in expression levels of a subset of herbivory responsive genes were further validated by RT-qPCR. Our study indicates that future elevated CO 2 concentrations will affect interactions between grapevine plants and one of its key insect pests, with consequences for future relevance of L. botrana in worldwide viticulture.

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Esca is an increasing threat to global viticulture causing significant losses by reducing yields, declining or wilting vines, and shortening the productive life of vineyards. Recent findings indicate that the disease may also affect the quality of grapes and the chemical composition of musts and wines. However, more research in this field is needed. Esca seems to affect the ripening process of grapes resulting in lower sugar content, higher acidity, and increased nitrogen concentrations. Regarding polyphenolic compounds, reduction on the concentrations of (+)-catechin, (−)-epicatechin, anthocyanins, and tannins has been observed due to the alteration of flavonoid metabolism. Esca is a complex-chronic disease, where several fungal pathogens act simultaneously or successively, to cause necrosis to the vascular tissues of grapevines by blocking the xylem vessels and by producing enzymes and phytotoxic metabolites. As genotype affects stress response, specific Vitis vinifera cultivars present higher levels of resistance to the disease than others. There is evidence that varieties such as Merlot, Grenache Rouge, and Roussanne are relatively resistant, compared with more susceptible Cabernet Sauvignon, Mourvèdre, Sauvignon Blanc, and Semillon. Another main objective of the current work was to investigate the possible effects of climate change on Esca development and propose appropriate control strategies.

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