黄瓜（Cucumis sativus L.）是具有重要经济价值的蔬菜作物，在全世界广泛栽培。霜霉病、白粉病和细菌性角斑病是黄瓜三种主要的叶部病害，对黄瓜的生产造成巨大的威胁。利用具有霜霉病、白粉病和细菌性角斑病三抗性的黄瓜品种是霜霉病、白粉病和细菌性角斑病抗性育种中最经济环保的方法。然而，绝大多数的黄瓜抗性材料仅具有霜霉病、白粉病和细菌性角斑病单一抗性或双抗性，同时具有霜霉病、白粉病和细菌性角斑病三抗性的黄瓜种质资源罕见报道。本研究基于多年多点的抗病性鉴定，发现黄瓜-酸黄瓜渐渗系材料IL52具有霜霉病、白粉病和细菌性角斑病三抗性，利用同时感霜霉病、白粉病和细菌性角斑病的黄瓜自交系‘长春密刺’（CCMC）与IL52构建的F1、193株F2群体和155个重组自交系（RILs）群体，基于田间成株期自然发病表型统计，分别对IL52中的霜霉病、白粉病和细菌性角斑病抗性进行遗传分析；采用BSA-seq分析和传统的QTL/基因定位方法，分别对IL52中的霜霉病、白粉病和细菌性角斑病抗性进行基因定位研究，阐明了IL52中霜霉病和白粉病双抗性的遗传关系，并预测了霜霉病和白粉病抗性候选基因，鉴定到与IL52中细菌性角斑病抗性基因紧密连锁的分子标记，主要研究内容与结果如下： 1. IL52霜霉病抗性遗传分析与QTL定位 基于亲本CCMC、IL52及其构建的155个RILs群体的3季成株期霜霉病田间自然发病表型统计结果，遗传分析发现IL52中的霜霉病抗性是多基因控制的数量性状；BSA-seq分析鉴定到4个霜霉病抗性QTLs，分别是DM1.1、DM5.1、DM5.2、DM5.3，其中DM5.3的平均Δ（SNP-index）达到了1，是一个非常显著的主效QTL；传统QTL定位研究检测到6个霜霉病抗性QTLs，分别是dm1.1、dm1.2、dm1.3、dm5.1、dm5.2和dm6.1，其中dm5.1和dm5.2是主效QTLs，其余都是微效QTLs；BSA-seq鉴定到的DM1.1、DM5.1、DM5.3分别与传统QTL定位检测到的dm1.2、dm5.1、dm.5.2位于相同物理区间，表明霜霉病抗性QTLs定位结果可靠，验证并缩小前人定位到的IL52中的抗霜霉病主效QTL dm5.2，并将该dm5.2定位到5号染色体上22.66-25.75 Mb区间内，其连锁标记为InDel73。 2. IL52白粉病抗性遗传分析与基因定位 基于亲本CCMC、IL52及其构建的F1、193株F2群体和155个RILs群体的成株期白粉病田间自然发病表型统计结果，遗传分析发现IL52中的白粉病抗性是由一个单隐性基因控制的质量性状；利用155个RILs群体，结合BSA-seq技术与传统基因定位手段，将白粉病抗性基因pm初定位到5号染色体上的23.21-25.70 Mb区间内，再利用193株F2群体和基于BSA-seq技术新开发的多态性标记，将pm精细定位到24,550,703-25,018,946 bp区间内，并鉴定到与pm完全共分离的标记SNP6，SNP6位于基因Csa5M622830.1的3′UTR区域，预测该GATA转录因子基因Csa5M622830.1是IL52中白粉病抗性候选基因。 3. IL52中霜霉病和白粉病双抗性遗传关系研究 研究发现dm5.2与pm位于5号染色体上相同的物理区间内，表明dm5.2与pm是连锁的，通过RILs群体的霜霉病和白粉病表型与基因型关联分析，发现连锁位点dm5.2/pm具有霜霉病部分抗性和白粉病完全抗性。基于BSA-seq分析，进一步发现dm5.2中的7个候选基因中，有3个发生相同变异类型的基因（Csa5M622800.1、Csa5M622830.1和Csa5M623490.1）也是pm的候选基因，预测这3个基因可能是霜霉病或白粉病抗性候选基因。 4. IL52细菌性角斑病抗性遗传分析与基因定位 基于亲本CCMC、IL52及其构建的F1、155个RILs群体的成株期细菌性角斑病田间自然发病表型统计结果，遗传分析发现IL52中的细菌性角斑病抗性是由一个单隐性基因控制的质量性状；结合BSA-seq分析和传统基因定位方法，将细菌性角斑病抗性基因psl定位到1号染色体3,118,855-3,951,558 bp区间内；并利用18个抗病RILs、18个感病RILs和19个感病黄瓜自交系中进行标记遗传连锁性检验，发现从BSA-seq分析中开发的多态性标记ALS-InDel与psl紧密连锁，可用于黄瓜细菌性角斑病抗性标记辅助育种。

Cucumber (Cucumis sativus L.) is an economically significant vegetable crop that cultivated worldwide. Downy mildew, powdery mildew and angular leaf spot are three important leaf diseases in cucumber, which posed huge threat on production of cucumber. Deployment of cucumber resistant cultivars with resistances to downy mildew, powdery mildew and angular leaf spot is the most economic and environment-friendly method for controlling the three diseases in cucumber breeding. However, most of the cucumber resistant materials only have single resistance or double resistances to downy mildew, powdery mildew and angular leaf spot. Cucumber germplasm resources with three kinds of resistances to downy mildew, powdery mildew and angular leaf spot were rarely reported. In this study, based on the evaluation of diseases resistance in different locations for several years, a Cucumis hystrix introgression line of cucumber IL52 with resistances to downy mildew, powdery mildew, angular leaf spot was identified. The F1, 193 F2 plants and 155 recombinant inbred lines (RILs) were constructed by cucumber inbred line CCMC with susceptibility to downy mildew, powdery mildew, angular leaf spot and IL52. Genetic analyses of downy mildew, powdery mildew and angular leaf spot resistance in IL52 were respectively performed based on the phenotypic data of natural epidemics on the plants at the adult plant stage in the field. Gene mapping of downy mildew, powdery mildew and angular leaf spot resistances in IL52 were respectively conducted by combining BSA-seq analysis and traditional QTL/gene mapping method. The genetic relationship of double disease resistances to downy and powdery mildew in IL52 was also illustrated. The candidate genes for resistance to downy and powdery mildew were predicted. The closely linked markers with the angular leaf spot resistance gene in IL52 were also identified. The main contents and results were shown as below: 1. Genetic analysis and QTL mapping of downy mildew resistance in IL52 Based on the statistical results of phenotypic data of natural epidemics of downy mildew exposed on the CCMC, IL52 and 155 RILs at adult plant stage in the field for 3 years, genetic analysis indicated that the downy mildew resistance in IL52 was controlled by polygenes. Following the method of BSA-seq analysis, 4 QTLs for downy mildew resistance were detected, which were DM5.1, DM5.2, DM5.3 and DM5.4, respectively. Of them, DM5.3 was a reliable major-effect QTL for downy mildew resistance with an average Δ (SNP-index) = 1. Traditional QTL mapping analysis identified 6 QTLs including dm1.1, dm1.2, dm1.3, dm5.1, dm5.2 and dm6.1 for downy mildew resistance. Among them, dm5.1 and dm5.2 were major-effect QTLs, the other QTLs were minor-effect. The genomic regions of DM1.1, DM5.1, DM5.3 identified by BSA-seq analysis were consistent with the chromosome intervals of dm1.2, dm5.1, dm.5.2 detected by traditional QTL mapping method respectively, which suggested that the QTL mapping analysis for downy mildew resistance in this study was reliable. Furthermore, as compared with the results from Pang et al. (2013), the genomic region of downy mildew resistance major-effect QTL dm5.2 in the present study was validated and narrowed down. dm5.2 was located within 22.66-25.75 Mb on chromosome 5, which was linked with marker InDel73. 2. Genetic analysis and gene mapping of powdery mildew resistance in IL52 Based on the statistical results of phenotypic data of natural epidemics of powdery mildew exposed on the CCMC, IL52, F1, 193 F2 plants and 155 RILs at adult plant stage in the field, genetic analysis indicated that the powdery mildew resistance in IL52 was controlled by a single recessive gene pm. Using the 155 RILs, pm was initially mapped into 23.21-25.70 Mb on chromosome 5 by combining BSA-seq analysis and traditional gene mapping method. Fine mapping of pm was further narrowed into 24,550,703-25,018,946 bp by using 193 F2 plants and newly developed polymorphic markers based on BSA-seq analysis. A perfectly co-segregating marker SNP6 with pm was also identified. SNP6 is present in the 3′UTR of Csa5M622830.1, which may be a likely candidate gene for powdery mildew resistance in IL52. 3. The study of genetic relationship of the double disease resistances to downy and powdery mildew in IL52 dm5.2 and pm were co-localized in the same physical interval on chromosome 5, which indicated that dm5.2 and pm were linked. The co-localized locus dm5.2/pm conferred partial resistance to downy mildew and complete resistance to powdery mildew. Based on BSA-seq analysis, the three candidate genes (Csa5M622800.1, Csa5M622830.1, Csa5M623490.1) for powdery mildew resistance were the same with three of seven candidate genes for downy mildew resistance, even the same as the amino acid change. The three genes were predicted as the candidate genes for resistance to downy mildew or powdery mildew. 4. Genetic analysis and gene mapping of angular leaf spot resistance in IL52 Based on the statistical results of phenotypic data of natural epidemics of angular leaf spot exposed on the CCMC, IL52 and 155 RILs at adult plant stage in the field, genetic analysis indicated that the angular leaf spot resistance in IL52 was controlled by a single recessive gene psl which was mapped into 3,118,855-3,951,558 bp on chromosome 1 by combining BSA-seq analysis and traditional gene mapping method. The polymorphic marker ALS-InDel developed from BSA-seq analysis was closely linked to psl by genetic linkage analysis in the 18 resistant RILs, 18 susceptible RILs and 19 susceptible cucumber inbred lines, which will be useful for marker-assisted breeding of angular leaf spot resistance in cucumber.