## 3 Elicitors and Their Classifications
### Elicitors Commonly Used on Grapevines  
Different classes of pathogens infect grapevines, reducing grape yield and quality. Fungi (_Botrytis cinerea_) and oomycetes (_Erysiphe necator_ and _Plasmopara viticola_) are the most persistent classes causing gray mold, powdery mildew, and downy mildew in grapes, respectively. These and several other diseases were initially treated and prevented with fungicides. Nevertheless, due to the negative impact of fungicides on the environment and the resistance of causative agents to fungicides [8; 92], elicitors are currently used as alternative preventive measures. However, the impact of elicitors on grapes is beyond the protection function. They also influence the volatile composition and sensory characteristics of grapes and wines. Several studies have reported the effective resistance induced by grapevine elicitors against diseases (Table 1) and their impact on the metabolites of elicited grapes (Table 2). Subsequent subsections of this review focus on some of the commonly used grapevine elicitors.  
Figure 3: Factors influencing the production of secondary metabolites in plant-elicitor interactions.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Elicitor** & **Grape** & **Defense Response** & **Reference** \\ \hline BTH, Laminarin (Lam), Potassium phosphonate (K-Pho) & Moscato, Nebbiolo & All products reduced disease incidence; significantly reduced disease severity; Moscato was less susceptible to the disease than Nebbiolo & [95] \\ \hline Nano-Methyl Jasmonate & Monastrell & Increased phytoaleoxins synthesis and lower cytotoxicity than MeJ & [96] \\ \hline Ozonated water & Bobal & limited grapevine infection by _Phaeocarcinomaium aleophilium_ & [97] \\ \hline COS-OGA & Carignan & Induced 78\% protection of grapes against powdery mildew in France and 76\% in Spain & [98] \\ \hline Flagellin and harpin & Pinot norir & ROS production; accumulation of _P_hotalexins; induction of defense genes; blocked extracellular alkalinization & [99, 100] \\ \hline Rhamnolipids & Gamay and Chardonnay & Inhibited spore germination and mycelium growth of _Botrytis cinerea_; SA synthesis; phytoaleoxin accumulation & [101] \\ \hline Sulfated laminarin (PS3) & Marselan & PS3 induced resistance against downy mildew under greenhouse conditions; elicited the emission of Volatile organic compounds; increased antimicrobial activity & [102, 103] \\ \hline Cellodext (CD) & Chardonnay & H\({}_{2}\)O\({}_{2}\) generation; increased calcium flux; ROS production; stimulation of chitinase and \(\beta\)-1,3 glucanase activities & [104] \\ \hline Chitosan & Chardonnay & Increased PAL and chitinase activities; reduced gray mold and downy mildew infections; increased stilbenes and phytoaleoxins accumulations & [105, 106, 107] \\ \hline Cyclodextrins & Gamay & Accumulation of phytoalexin; peroxidase activity induction & [108] \\ \hline Ergosterol & Ugni Blanc & Enhanced protection against _Botrytis cinerea_ & [109] \\ \hline Benzothiadiazole (BTH) & Merlot & Enhanced trans-resveratrol content, anthocyanin synthesis; induced SAR; decreased _Botrytis cinerea_ infection; increased total polyphenols & [110, 111] \\ \hline \(\beta\)-aminobutyric acid (BABA), Jasmonic acid (JA) & Chasselas and Solaris & Callose and lignin deposition; increased resistance against downy mildew; expression of LOX-9 and PR-4 genes & [112] \\ \hline Methyl Jasmonate (MeJ) & Cabernet Sauvignon & Induction of peroxidase, chitinase, and, glucanase activities; phytoplankton accumulation & [113] \\ \hline Ethephon & Cabernet Sauvignon & Increased number of PR-proteins; enhanced phytoalexin biosynthesis; induced protection against _Eryspine reactor_ & [114] \\ \hline Soybean and casein & Marselan & Enhanced grapevine immunity against _Plasmoparan vitticola_ attack & [115] \\ \hline Methyl Jasmonate (MeJ) & Barbera & Increased berry resveratrol and _E_-vriniferin production & [116] \\ \hline \end{tabular}
\end{table}
Table 1: List of Some Elicitors and their Defense Impact on Different Grape Cultivars.