Field Crop 2025, Vol.8, No.2, 93-101 http://cropscipublisher.com/index.php/fc 95 3.3 Biochemical defense The phenolic substances in grape skins are not just for show. Maia et al. (2020) confirmed that these things can both strengthen cell walls and directly kill pathogens. Flavonoids are even more powerful. Ferrandino et al. (2023) found that it is not only antioxidant, but also "tip" other defense systems. What is particularly interesting is that gray mold and downy mildew actually trigger different chemical defenses-the former stimulates anthocyanin synthesis, while the latter mainly activates chalcone enzymes (Figure 2). Figure 2 A schematic representation of the networks of hormonal and molecular signals regulating the secondary metabolism in the grapevine berry in response to Botrytis cinerea (Adopted from Ferrandino et al., 2023) Image caption: (A) A grape bunch of Vitis vinifera cv Chardonnay showing very initial symptoms of Botrytis cinerea infection. (B) At the berry level, both NR (Noble Rot) and BR (Bunch Rot) infection induce an increase in DPA (dihydrophaseic acid) and ABA (abscisic acid) concentrations (Adopted from Ferrandino et al., 2023) When it comes to enzymes, we have to mention two "model workers": peroxidase is responsible for cleaning up toxic oxides (Castro et al., 2023), and PAL enzyme is the "chief engineer" for synthesizing phenolic substances (Gauthier et al., 2014). They are like switches for the defense system, which can directly kill the enemy and activate systemic immunity. 3.4 Physical barriers The wax on the surface of grapes is not just for looks. Ferrandino et al. (2014) pointed out that this layer of cuticle can both prevent bacteria and lock in moisture. If the bacteria force their way through, the grapes will urgently thicken the cell wall at the wound-the electron microscope photos taken by Santos et al. (2020) show that lignin will accumulate quickly at the infected site, just like cementing a city wall. However, this defense consumes a lot of energy, so it will only be activated when the bacteria are detected (Castro et al., 2023). 4 Strategies for Breeding Grapes Resistant to Biotic Stresses 4.1 Traditional breeding methods You may not believe it, although molecular breeding is very popular now, traditional hybrid breeding is still very effective in the field of grape disease resistance. Take powdery mildew as an example. Researchers found that the Run1 gene in wild grape Muscadinia rotundifolia and the REN1 gene in cultivated grape Vitis vinifera are particularly effective. Putting these two genes together, the new varieties bred are extremely resistant to powdery mildew fungus Erysiphe necator (Agurto et al., 2017). However, it should be noted that this kind of gene stacking is not a simple matter, and it has to be done little by little through hybrid breeding. Merdinoglu et al. (2018) found that the reason why these new varieties are so powerful is that they can quickly produce disease-resistant substances and activate defense genes.
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