Molecular Pathogens, 2025, Vol.16, No.4, 182-192 http://microbescipublisher.com/index.php/mp 189 European and American hybrids. There are basically no downy mildew spots in the fields and are considered to have immune resistance. Analysis found that it may carry the Rpv10 and Rpv12 resistance genes derived from Shanxi Grape. 6.3 Molecular marker development and breeding application of resistant varieties To apply the above-mentioned genetic characteristics of downy mildew resistance to actual breeding, it is necessary to achieve effective selection of target genes with the help of molecular markers. Since the discovery of the first downy mildew-resistant QTL (Rpv1), researchers have begun developing DNA markers closely linked to these QTLs for assisted breeding screening. After years of hard work, a series of molecular marker systems that resist downy mildew genes have been established. For example, for Rpv1, the specific SSR marker UDP-Perf can distinguish plants carrying resistant fragments of round leaf grapes (Goyal et al., 2021); for Rpv3, multiple markers have been widely used in European disease-resistant breeding programs to screen whether hybrid seedlings carry this resistance site. With the development of high-throughput sequencing technology, genome-wide selection (GS) has also begun to be tried in grape breeding. GS analyzes a large number of markers in the entire genome to construct a predictive model of disease-resistant traits, which can consider the role of multiple micro-effect genes at the same time, making it more effective in selecting complex traits (Possamai et al., 2024). This technology is expected to further accelerate the cultivation of disease-resistant varieties. In the practice of downy mildew-resistant breeding, the value of marker-assisted selection (MAS) has been proven. In China, the Northeast region has shortened the hybrid breeding cycle of mountain grapes and Eurasian species through MAS selection, and has cultivated new disease-resistant wine grape varieties such as ‘Beifang No. 14’, which are currently under regional trials. 7 Resistance Molecular Labeling and Molecular Breeding 7.1 Application of molecular markers such as SSR and SNP in resistance identification Molecular markers are an important tool for identifying disease-resistant genes in modern breeding. In the field of grape downy mildew resistance research, simple repeat markers (SSR) and single nucleotide polymorphism markers (SNPs) are widely used in resistance gene localization and vector material screening. Due to its co-dominant and high polymorphism, SSR markers are suitable for genotyping of highly hybrid substances such as grapes. In China, Ma Lixian and others used the enrichment SSR method to develop hundreds of grape SSR markers and used some of these markers to genotype resources such as mountain grapes to prepare for disease-resistant gene location. In the past decade, the rise of second-generation sequencing has promoted the large-scale application of SNP markers. SNP markers have the advantages of a huge number and covering the entire genome, and can meet the needs of high-density linkage mapping and genome-wide association analysis. In actual resistance identification, SNP markers are often used in the form of KASP or chips for high-throughput screening (Wairich et al., 2021). There are already commercial 9K and 18K grape SNP chips abroad that can detect tens of thousands of SNPs at a time, providing convenience for the whole genome scanning and auxiliary selection of resistance genes. In addition to SSR and SNP, amplified fragment length polymorphisms (AFLP), insertion deletion markers (InDel), etc. are also used, but are less used due to stability and flux reasons. 7.2 Advances in application of marker-assisted selection (MAS) and genome selection (GS) Marker-assisted selection (MAS) is an important technical means to apply the above-mentioned molecular markers to actual breeding processes. MAS has shown significant results in grape downy mildew resistance breeding. Traditional grape breeding takes many years to identify disease-resistant plants morphically. With the help of MAS, we can identify individuals carrying disease-resistant genes in advance through DNA testing during the seedling stage, which greatly saves manpower and time. In the selection and breeding of new disease-resistant varieties in France, hybrid offspring were tested for Rpv1 and Rpv3, and only double-label positive plants were retained and the number of candidates was successfully reduced by more than 70%, but the target disease-resistant plants were almost not missed (Schneider et al., 2019). The successful application of MAS is also reflected in the optimization of parental selection. In the disease-resistant polymer breeding of seedless grapes in Xinjiang,
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