| Cucumber(Cucumis sativus L.,2n=14)is one of the ten largest vegetable crops in the world.The planting area of cucumbers in China ranks first in the world.However,due to the narrow genetic basis,cucumber is lack of important resistance genes,and diseases are common in production.Downy mildew is one of the most serious diseases threatening cucumber production.Cucumis hystrix Chakr.(2n=24)is the only rare wild species that can be successfully hybridized with cultivated cucumber,and has a resistance gene to many diseases including downy mildew.The discovery and utilization of the excellent resistance genes of wild relatives of cucumbers is an important way to improve the resistance of cultivated cucumber to downy mildew.Molecular marker-assisted modern breeding technology has the advantages of high efficiency,speed and accuracy.Based on previous genetic mapping and marker development,this study developed a molecular marker assisted transfer technique for downy mildew resistance,and successfully transferred the disease resistance gene of cucumber-Cucumis hystrix Chakr introgression line IL52 to cucumber varieties with good comprehensive shape but less resistant to downy mildew.Including 18363S,18461S,18043S and 18042S,and the identification of disease resistance was carried out.1 On the basis of previous work,this study screened 2 Indel markers linked to cucumber downy mildew resistance genes,and 8 polymorphic general-purpose markers with 8 high quality parents and IL52 in 18363S,18461S,18031S,18019S,18026S,18364S,18043S and 18042S.The differences between two and two markers were significant.The genotyping effect of 17ID73 was better,so we chose 17ID73 as the main marker for screening.2 The study of molecular marker assisted breeding of Cucumber-Cucumis hystrix Chakr introgression line IL52 downy mildew resistance was carried out.Based on the selection of molecular markers and identification of comprehensive characters,the main resistance loci DM5.2 of downy mildew resistance were transferred to four parent materials,including 18363s,18461s,18043s and 18042s,and four parent materials were hybridized with IL52.The marker screened the resistant plants and continued backcrossing,repeated screening and backcross,and the selfing separation and disease resistance identification were carried out until the four generation of backcross.The new cucumber variety 18363s with both disease resistance and excellent characters was allocated to the backcross three generation,18461s new varieties were allocated to the backcross three generation,and the new 18043 s varieties were allocated to the backcross two generation.The new varieties of 18042s were allocated to the three generation of backcross.In the next study,we should continue to carry out the improvement to the four generation of backcross,and identify the resistance to downy mildew after the selfing separation.3 In the 3 quarters of autumn 2018 to autumn 2019,four kinds of parental materials 18363s,18461s,18043s,18042s,donor IL52 were identified in the field,and the downy mildew resistance of cucumber variety NING KANG ER HAO,which was carried out by IL52 from different generations,and DM5.2,which was resistant to IL52 downy mildew resistance,was identified to a certain extent,the stability and reliability of the markers linked to downy mildew resistance were proved.Four kinds of receptor parental materials were susceptible,donor IL52 was resistant to disease,and all generations of materials in the process of improvement were all susceptible to heterozygous genotype.General marker assisted selection needed to be combined with marker selection and phenotypic identification.However,because the main loci of downy mildew resistance in this study were DM5.2 recessive traits.Under the premise of reliable and stable breeding mark,resistance identification can be carried out only after the breeding process enters the final selfpurification link. |
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