Field Crop 2025, Vol.8, No.2, 93-101 http://cropscipublisher.com/index.php/fc 97 6 Successful Case Studies 6.1 Breeding of powdery mildew-resistant varieties Due to the severe economic impact of powdery mildew (caused by Erysiphe necator), the development of powdery mildew resistant grape varieties has been an important research direction in the field of grape cultivation. The defense capabilities of grape varieties such as ‘Crimson Seedless’ were significantly enhanced through the stacking breeding strategy of resistance genes such as Run1 and REN1. These hybrids exhibited strong resistance mechanisms, including reactive oxygen species (ROS) production and gene activation, which effectively prevented the establishment and growth of pathogens (Agurto et al., 2017). In addition, Wan et al. (2020) showed that the editing of the susceptible gene VvMLO3 using CRISPR/Cas9 technology changed the growth characteristics of grape plants and their response to pathogen infection. Obvious trypan blue staining and H2O2 accumulation were observed in the mutant lines, indicating an enhanced cellular response to infection (Figure 3). The VvMLO3 gene can play an important role in disease defense by regulating disease resistance-related signaling pathways in leaf cells, providing a new gene target for improving grape disease resistance, thereby obtaining grape lines with stronger resistance to powdery mildew, further demonstrating the potential of genetic engineering in breeding programs. The market performance of these hybrids is promising, as they provide long-lasting resistance without compromising grape quality and are an important resource for sustainable grape cultivation (Yu et al., 2024). 6.2 Development of grape phylloxera-resistant varieties Grape phylloxera is a pest that damages grape roots and has traditionally been managed by using resistant rootstocks. Breeding programs have successfully utilized resistance genes naturally present in the American Vitis species to develop phylloxera-resistant grape varieties. These efforts have played a key role in maintaining grape production in areas severely infested with grape phylloxera. Integrating phylloxera-resistant genes into Vitis vinifera cultivars not only maintains the production of high-quality grapes, but also reduces dependence on chemical treatments. 6.3 Multi-resistant grape varieties The development of grape varieties resistant to multiple diseases, such as powdery and downy mildew, requires the strategic stacking of resistance genes. For example, the PIWI grape variety was developed through traditional breeding methods with resistance to Erysiphe necator and Plasmopara viticola. These varieties are often bred by crossing with American or Asian grape varieties that carry natural resistance. Transcriptional analysis of these varieties revealed specific gene expression patterns that contribute to their disease resistance, providing important insights into the molecular mechanisms of multi-disease resistance (Scariolo et al., 2024). Such multi-resistant varieties are essential for sustainable grape cultivation as they reduce the need for chemical fungicides and improve the environmental and economic sustainability of grape production (Merdinoglu et al., 2018). 7 Current Challenges and Future Directions 7.1 Complexity of gene-environment interactions When it comes to disease resistance in grapes, environmental factors are often a headache. Wang et al. (2023) found that rootstocks perform very differently in different places-some places can resist phylloxera, but in other places they may not even be able to resist nematodes. Of course, there are exceptions. For example, the Santos et al. (2020) noticed that some varieties have a relatively stable response to the Plasmopara viticola pathogen. In general, resistance genes are really difficult to control in a changing climate. 7.2 Limitations of germplasm resources There are a lot of good things hidden in wild grape germplasm, as Ricciardi et al. (2024)’s recent studies have confirmed. But the reality is that the germplasm banks we have are really limited. Although in theory, protecting more genetic diversity can provide more options for breeding, such as the resistance traits discovered by Sargolzaei et al. (2020). But the problem is that it is not easy to collect and preserve so many resources in practice. 7.3 Technical challenges in biotic stress research Nowadays, GWAS and transcriptome technologies have really helped a lot in grape disease resistance research. Fröbel et al. (2019) used these methods to find key resistance sites. But then again, these high-end technologies
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