Molecular Pathogens, 2025, Vol.16, No.4, 182-192 http://microbescipublisher.com/index.php/mp 184 Further analysis showed that the difference in pathogenicity of strains in the same region was not directly related to their geographical origin, and the disease resistance background of the host variety is the main factor affecting the disease index. This result emphasizes the need to consider the pathogenic dynamics of the pathogenic population when promoting disease-resistant varieties. A study conducted by another team compared the pathogenicity of downy mildew bacteria in Jiangsu and Zhejiang. They collected monosporous strains of pathogenicity from multiple production areas of Jiangsu and Zhejiang provinces, and used leaf disc inoculation method to determine the pathogenicity. They found that the strains in both places can be divided into three pathogenicity types: strong, medium and weak (Li et al., 2016). The strong pathogenic strains account for a relatively high proportion in Jiangsu samples, while in Zhejiang, the moderate pathogenic strains are the main ones. In the same province, the average pathogenicity of strains from different production areas also varies: for example, the pathogenicity of isolates in Shushan, Jiangsu and Yongfu production areas in Zhejiang is significantly higher than that of other production areas in this province. Figure 1 Histochemical observation of LJ-Pv18001 in grapevines. Histochemical staining was performed to detect cell death and Hypha growth at 0 hpi, 12 hpi, 24 hpi, 48 hpi, and 96 hpi, with trypan blue and aniline blue staining (Adopted from Wu et al., 2025) 3 The Genetic Basis of Grape Downy Mildew Resistance 3.1 Distribution and identification of resistance genes (Rgenes) in grapes Grapes have a clear genetic basis for resistance to downy mildew. Some wild grape species (especially North American and Asian species) have developed genetic properties that resist downy mildew in long-term evolution, which is closely related to the resistance genes carried therein. Most known disease-resistant genes belong to the nucleotide-binding-leucine-rich repeat sequence (NBS-LRR) R gene family, which can specifically recognize pathogenic effector proteins and initiate immune responses. In grapes, multiple downy mildew-resistant R genes or R gene homologous sequences have been isolated and identified from different species. For example, a CC-NBS-LRR type R gene VqCN was cloned from disease-resistant Chinese wild grape thick skin grape (V. quinquangularis), whose expression level was significantly upregulated with bacterial infestation in the disease-resistant context. In the disease-resistant mountain grape (V. amurensis), researchers identified a series of disease-resistant related genes (commonly known as RGA): For example, the VaRGA1 gene is believed to be closely related to downy mildew resistance, and overexpression can increase the resistance of pattern plants to bacteria. In addition, there is the VpRPW8 gene family from wild hair grapes (V. pseudoreticulata). RPW8 is a broad-spectrum disease-resistant gene. Lai Yanhong and others from Xinjiang Agricultural University found through molecular cloning and functional analysis that overexpression of VpRPW8s can enhance the resistance of tobacco to oomycosis pathogens. These studies show that wild grapes contain rich disease-resistant R gene resources, and the identified R genes are distributed on multiple chromosomes.
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