Three Types of Elicitors Induce Grapevine Resistance against Downy Mildew via Common and Specific Immune Responses.

Three recognized plant defense stimulators (PDS), methyl jasmonate (MeJA), benzothiadiazole (BTH) and phosphonates (PHOS), were sprayed on grapevine Vitis vinifera cuttings and conferred resistance to the biotrophic pathogen Plasmopara viticola. The effects on molecular defense-related genes and polyphenol content (stilbenes and flavanols) were revealed at 6 and 8 days post-elicitation. The transcript accumulation was consistent with the signaling pathway specific to the elicitor, salicylic acid for BTH, and jasmonic acid for MeJA, with some cross-talks. PHOS tended to modulate the defense responses like BTH. Moreover, in response to a downy mildew inoculation, the leaves pre-treated with PHOS and BTH overproduced pterostilbene, and after MeJA treatment, piceids and ε-viniferin, compared to uninoculated elicitor-treated leaves. These results provide evidence of the different modes of action of PDS and their role in sustainable viticulture.

Grapevine Stimulation: A Multidisciplinary Approach to Investigate the Effects of Biostimulants and a Plant Defense Stimulator.

The increasing use of plant defense stimulators (PDS) and biostimulants (BS) to make agriculture more sustainable has led to questions about their action on plants. A new PhysBioGen approach is proposed with complementary tools: PHYSiological (root weight); BIOchemical and BIOlogical (secondary metabolite quantification and Plasmopara viticola development) and expressions of 161 GENes involved in metabolic plant functions. The proposed approach investigated the effects of three phytostimulants on Vitis vinifera: one PDS (ASM) and one BS chelated (CH) and another enriched with seaweed (SW). Distinct responses were obtained between the PDS and the two BS. In particular, we observed the persistence of anti-mildew efficacy over time, correlated with differentiated expressions of defense genes (VvROMT, VvSAMT, VvPR8). As expected, the two BS displayed more similarities to each other than to the PDS (flavonols, anthocyanins, free salicylic acid). However, the two BS revealed differences in the modulation of genes involved in defense and primary metabolism and some genes were identified as potential markers of their action (VvWRKY1, VvLOX9, VvPOD, VvPDV1, VvXIP1, VVDnaJ). Our results highlight the common and the specific effects of the two BS and the PDS. These new tools could help in understanding the mode of action of phytostimulants in order to achieve better quality and production yield and/or as a way to limit chemical inputs in the vineyard.

Impact of different elicitors on grapevine leaf metabolism monitored by 1H NMR spectroscopy.

INTRODUCTION: Grapevine protection is an important issue in viticulture. To reduce pesticide use, sustainable disease control strategies are proposed, including a promising alternative method based on the elicitor-triggered stimulation of the grapevine natural defense responses. However, detailed investigations are necessary to characterize the impact of such defense induction on the primary metabolism. OBJECTIVES: Our aim was to use a metabolomics approach to assess the impact on grapevine of different elicitors dependent on the salicylic acid (SA) and/or jasmonic acid (JA) pathway. For this purpose, leaves of grapevine foliar cuttings were treated with methyl jasmonate, acibenzolar-S-methyl or phosphonates. METHODS: According to the elicitor, common and discriminating metabolites were elucidated using 1H NMR measurements and principal component analysis. RESULTS: A wide range of compounds including carbohydrates, amino acids, organic acids, phenolics and amines were identified. The score plots obtained by combining PC1 versus PC2 and PC1 versus PC3 allowed a clear separation of samples, so metabolite fingerprinting showed an extensive reprogramming of primary metabolic pathways after elicitation. CONCLUSION: The methods applied were found to be accurate for the rapid determination and differential characterization of plant samples based on their metabolic composition. These investigations can be very useful because the application of plant defense stimulators is gaining greater importance as an alternative strategy to pesticides in the vineyard.

Comparison of the Impact of Two Molecules on Plant Defense and on Efficacy against Botrytis cinerea in the Vineyard: A Plant Defense Inducer (Benzothiadiazole) and a Fungicide (Pyrimethanil).

Grapevine is subject to diseases that affect yield and wine quality caused by various pathogens including Botrytis cinerea. To limit the use of fungicides, an alternative is to use plant elicitors such as benzothiadiazole (BTH). We investigated the effect of a fungicide (Pyrimethanil) and an elicitor (benzothiadiazole) on plant defenses. Applications for two consecutive years in the vineyard significantly reduced gray mold. Two and seven days after treatments, the expressions of 48 genes involved in defenses showed differential modulation (up- or down-regulation) depending on treatment. Some genes were identified as potential markers of protection and were linked to an increase in total polyphenols (TP) in leaves. Surprisingly, the fungicide also induced the expression of defense genes and increased the polyphenol content. This suggests that BTH acts as an efficient elicitor in the vineyard and that Pyrimethanil may act, in part, as a defense-inducing agent on the vine.