Grapevine is subject to a number of diseases that affect yield and wine quality. To limit the excessive use of phytochemicals in the vineyard, alternative strategies have to be developed. Plant treatment with signaling molecules like elicitors stimulates their natural defense mechanisms. To improve grapevine tolerance against fungal pathogens, Vitis vinifera plants were treated with a natural exogenous elicitor, methyl jasmonate (MeJA). MeJA-treated leaves (Cabernet Sauvignon foliar cuttings) reacted by increasing transcript levels coding pathogenesis-related proteins (acidic class IV chitinase, serine protease inhibitor, polygalacturonase-inhibiting protein, and beta-1,3-glucanase) and coding enzymes involved in phytoalexin biosynthesis (one phenylalanine ammonia lyase and one stilbene synthase). This was correlated with the accumulation of stilbenes (antimicrobial compounds). The eliciting activity of MeJA was confirmed by enhanced tolerance of grapevine foliar cuttings and vineyard against powdery mildew (75% and 73%, respectively). On the basis of these original results, MeJA can therefore act as an efficient elicitor in an alternative strategy of grapevine protection.

Benzothiadiazole (BTH), a salicylic acid analogue, strengthens plant defence mechanisms against a broad spectrum of pathogens. The role of pre-treatment with BTH in enhancing resistance against infection with various isolates of downy and powdery mildews (Plasmopara viticola and Erysiphe necator) was investigated in grapevine leaves. Tools were developed to better assess the defence status of the plant. In compatible interactions amongst a set of 19 genes, more than 57AE2% of differentiated transcripts from P. viticola infected-leaves (Pv-infected leaves) and 90% from E. necator-infected leaves (En-infected leaves) were down-regulated at 24 h post-inoculation (hpi), indicating a manipulation of host responses by the pathogens. BTH treatment enhanced grapevine defences, with pathogen growth inhibited by 61-98%, depending on the pathogen isolate. Treatment also triggered up-regulation of pathogenesis-related protein genes such as PR-1, PR-2, PR-3, PR-8 and PR-10 in Pv-infected leaves, and PR-3, PR-6 and PR-10 in En-infected leaves. Treatment with BTH also led to regulation of indole pathway transcripts; in particular, anthranilate synthase was down-regulated at 24 hpi in all infected leaves, then strongly up-regulated afterwards according to the rate of pathogen development. Quantitation of polyphenols and stilbenes showed that pterostilbene was specifically accumulated in pre-treated leaves and associated with biological efficacy and significant increases in PR protein gene transcripts. The temporal evolution of defence-related genes in pre-treated infected leaves suggests that grapevine responses vary depending on the inter-or intra-species variability of pathogens.

The grapevine (Vitis vinifera) is susceptible to many pathogens such as Botrytis cinerea, Plasmopara viticola, Erysiphe necator, and Eutypa lata. Phytochemicals are used extensively in vineyards to reduce pathogen infections, but the appearance of pesticide-resistant pathogen strains and the need for environmental protection require the use of alternative strategies. The phytohormone ethylene is assumed to play a role in the development of disease resistance. In the present study, we have treated grapevine foliar cuttings (Cabernet Sauvignon) with ethylene-releasing ethephon. This resulted in an increase in the number of pathogenesis-related protein (CHIT4c, PIN, PGIP, and GLU) gene copies and in an enhancement of phytoalexin biosynthesis by inducing the PAL and STS genes that correlated with the accumulation of stilbenes (antimicrobial compounds). Moreover, ethephon treatment triggered the protection of grapevine detached leaves and grapevine foliar cuttings against Erysiphe necator, the causal agent of powdery mildew (64% and 70%, respectively). These studies emphasize the major role of ethylene in grapevine defense.

The biotrophic fungus, Erysiphe necator the causal agent of the grape powdery mildew, has two genetic groups A and B in European and Australian vineyards. A strain of group A was used to isolate a DNA sequence that exhibits high sequence homology to RNaseH of a non-LTR (long tandem repeat) retrotransposon of Glomerella cingulata. PCR primers were designed and tested for their specificity to genetic group A of E. necator. This molecular tool is more efficient and sensitive than nested PCR based on polymorphism in the CYP 51 and b-tubulin genes.