Germplasm Identification Of Waterlogging Tolerant And QTL Mapping For Waterlogging Tolerance In Cucumber

Cucumber（Cucumis sativus L.）is an annual climbing herbaceous plant of the gourd family and is one of the main vegetable crops widely cultivated in China.With global warming,storms and floods are occurring more frequently.Cucumber root system has the characteristics of shallow soil penetration,underdeveloped aeriated tissue and poor regeneration ability,so it is sensitive to waterlogging.Therefore,it is of great theoretical and practical significance to explore waterlogging toleranttnrelot germplasm so as to rationally select and directionally cultivate waterlogging resistant varieties and reduce the harm of waterlogging stress on cucumber growth.In this study,299 core cucumber germplasm resources were waterlogged,and the change of the number of adventitious roots and chlorophyll content were recored and used to genome-wide association analysis.In addition,an F2 populations,was used to map the major effect QTL controlling waterlogging tolerance.The main research results are listed as follows:1.A total of 299 core cucumber germplasm used in this study.Adventitious root number and relative chlorophyll before and after waterlogging were used as two important indexes to assess the waterlogging tolerance ability.The results showed that the phenotypic variation of related traits of cucumber germplasm resources was extensive,and the relative chlorophyll variation range ranged from-28.90 to 3.40,with an average of-9.10.The number of adventitious roots ranged from 6.00 to 89.00,with an average of 34.00.There were obvious normal distribution characteristics,which indicated that the waterlogging tolerance of cucumber seedling was controlled by multiple genes.Finally,three waterlogging resistant strains（YZ019A,YZU178A and YZ026A）were screened out in this experiment.Three waterlogging resistant strains（YZ106A,YZ273,YZ196）.2.A total of 1625341 SNPS and 339618 InDels were detected in 299 cucumber germplasm samples by genome resequencing,and the attenuation distance of linkage imbalance was 10.6kb.The results of population structure analysis showed that there were four optimal subpopulations（ΔK=0.455）for 299 cucumber germplasm resources,which were east Asia,Eurasia,North America and India.The results of genetic analysis showed that 54.3%of the materials had zero genetic relationship,indicating that most of the materials in this population had no genetic relationship.3.Genome-wide association analysis was conducted on 1625341 SNPs for the changes in adventit root number and relative chlorophyll content before and after waterlogging,and a total of 10 loci significantly associated with cucumber waterlogging tolerance were detected,located on chromosome 2,3,4,6,7 respectively.CsaV3₆G006700 and CsaV3₇G018820 were obtained in this linkage imbalance region.CsaV3₆G006700 and CsaV3₇G018820 encode pectin esterase inhibitors and proteins containing the SWIB complex BAF60b structural protein domain,respectively.4.Take waterlogging resistant variety YZ026A and waterlogging resistant variety YZ106A as parent material,and configure F2 population.It was found that the phenotype was a typical quantitative trait with a continuous and single-peak distribution in the number of adventitious roots of hypocotyl after flooding in F2 population.Two F2 populations of 220 and 417 were selected to form the adventitious root-producing pool and the non-adventitious root-producing pool respectively.BSA sequencing combined with classical QTL-SEQ mapping was performed on the two groups of extreme mixed pool.The main QTL for controlling cucumber waterlogging tolerance was preliminarily mapped,and a major QTL for controlling cucumber waterlogging tolerance was found on chromosome 2 with a physical distance of～22.8kb（Chr2:18739682-18762497bp）,and there were 5 genes in this range.