Field: Vegetable genetics and breeding Traditional breeding relies on the selection of field traits and is susceptible to environmental and explicit and recessive influences, with large errors and low efficiency. Molecular breeding directly selects target traits at the genomic level through molecular markers, which can overcome the bottleneck of traditional breeding. Previously, research on cucumber molecular breeding was lagging behind and had not yet entered substantive application. With the support of 863 and other projects, the project team spent 18 years building a cucumber molecular marker breeding technology system, cultivating 4 new varieties and promoting them on a large scale. Important results have been achieved as follows: 1. It took the lead in creating the most saturated molecular marker genetic map of cucumber in the world, and located 172 QTL loci for 22 agronomic traits, with a selection efficiency of 86%, solving the problem of difficulty in selecting quantitative traits in traditional breeding. Problem. Many important characters in cucumber are quantitative characters, controlled by multiple genes and susceptible to environmental impacts. Molecular marker genetic maps help locate quantitative traits and significantly improve the selection accuracy of traits such as yield and quality. Among the 11 atlas published at home and abroad, the project team completed 7. The integrated genetic map covers North China, European, processed and wild cucumber resources, and contains 1369 SSR markers, with the highest accuracy and is suitable for all cultivated cucumbers. Based on the high-density map, a total of 22 traits and 172 QTL were mapped, accounting for 90% of the number of similar QTL at home and abroad, ranking at the international leading level. 2. For the first time, 8 quality trait genes related to yield, quality, and disease resistance were finely mapped, and the invented molecular markers were used to achieve a screening accuracy of more than 98%. For quality traits determined by a few genes, map cloning was used for fine mapping. The first to obtain the unisexual flower gene M, which provides a selection basis for realizing the all-female type of cucumber and the high-yield characteristics of fruit bearing per node; the first to obtain the gene related to cucumber fruit tumors and fruit thorns (Tu/Mrit/Tril/Ts) and the fruit dullness gene D and fruit color gene u, enabling the selection of fruit quality traits at seedling stages; the major powdery mildew resistance gene (mlo) in cucumber has been obtained for the first time in the world, achieving 100% screening accuracy of anti-powdery mildew genes. For the first time, molecular markers closely linked to traits such as holo-female type, fruit apparent traits, powdery mildew resistance, and virus disease ZYMV have been invented. The selection accuracy rate can reach more than 98%, breaking through the selection bottleneck of traditional breeding that is influenced by the environment and traits. 3. For the first time, a database of phenotypes and molecular markers of cucumber germplasm resources was created, the cucumber molecular breeding technology system was innovated, the technical problem of difficulty in aggregating high-quality and disease-resistant genes was overcome, breeding efficiency was increased by 5 times, and new high-quality disease-resistant varieties were cultivated. 4. Genetic diversity analysis was carried out on 177 representative cucumber materials using molecular markers. The group matching degree between molecular marker analysis and phenotypes reached more than 95%. The germplasm resource bank established using molecular markers and phenotypes laid the foundation for precise breeding. By applying the 195 molecular markers of qualitative and quantitative traits that have been invented, a technological breakthrough in determining target traits in prospect selection and retaining high-quality traits in background selection has been achieved, accelerating the breeding process and creating new varieties that aggregate high-quality traits and are resistant to disease. 4 varieties. Demonstration bases have been established in many provinces and cities, and seed companies have jointly promoted new cucumber varieties, with a total promotion area of 749,000 acres and an additional economic benefit of 2.8069 billion yuan. It has obtained 15 authorized invention patents, applied for 10 patents, approved 4 new varieties, published 69 related papers, and was cited a total of 2348 times, including 30 SCI papers, with a cumulative impact factor of 69.13, and was cited 1043 times. According to the novelty search certificate and peer review, the project's cucumber genetic map, QTL analysis, gene fine mapping and map cloning research have reached the international leading level.