Ovary Culture And QTL Mapping Of Tuberculate Fruit Position And Multiple Female Flower In Cucumber

Cucumber（Cucumis sativus L.）is the important vegetable crops in our country.Drought cucumber is the dominant characteristic industry in hebei province,but drought cucumber breeding started late and the breeding technology lagged behind,which restricted the efficiency of drought cucumber breeding.It is of great significance to establish a technique system of unpollinated ovary culture of drought cucumber,to locate important agronomic traits QTLs and to excavate candidate genes.In this paper,the technique system of unpollinated ovary culture of cucumber was studied,and genetic analysis and QTL mapping were carried out for tuberculate fruit position of multiple female flower and fruit tumor of cucumber based on BSA-seq technology.The main results were as follows:1.The effects of genotypes,different stages of ovary development and sampling time,TDZ at different mass concentrations,and temperature on female nucleus induction were studied in the unpollinated ovary of four different genotypes of cucumber.The results showed that the effects of different genotypes on the development of female nucleus were significantly different,and the female nucleus initiation rate of’1503’was the highest（77.22%）.The sample 1 day before flowering was the best,and the initiation rate of’1503’female nucleus was 95.56%.With the increase of TDZ mass concentration,the initiation rate of female nucleus increased first and then decreased.Among them,the initiation rate of’1503’treated with 0.08mg·L^-1 TDZ was the highest,reaching 91.6%.After dark culture at 35℃for 4 days,the female nucleus initiation rate was the best,up to 78.33%.In this study,the optimal technique system for inducing female nucleus in unpollinated ovary culture of cucumber was as follows:1 day before flowering,unpollinated ovary was used as material,and dark culture was conducted at 35℃for 4 days on the induction medium with 0.08 mg·L^-1 TDZ.2.An F₂ generation separation population was constructed by’9 dong 6’（single pistillate flower,female parent）and Tuzitui’（multiple female flower,male parent）and BSA-seq was used to analyze the QTL of multiple female flower in cucumber.The results showed that the multiple female flower of cucumber was partially recessive to the single female flower.The distribution of multiple female flower node rate（53.5%）in F₂ population showed a multi-peak,with obvious quantitative genetic characteristics of main gene+polygene.The candidate gene loci regulating the multiple female flower of cucumber were located on chromosome 2（3.09 Mbp-20.56Mbp）and chromosome 5（4.55 Mbp-4.60 Mbp）.Further analysis revealed that there were 18 candidate genes in this region.CsaV3₂G015930（13.230 Mbp-13.231 Mbp）,CsaV3₂G025610（17.600 Mbp-17.602 Mbp）and CsaV3₂G027940（18.474Mbp-18.479 Mbp）were identified by by NCBI database annotation.Among them,CsaV3₂G015930,encoding a AP₂/B₃ transcription factor family protein,is located in the overlapping region of chromosome 2（13.12 Mbp-13.23 Mbp）,and may play a certain role in flower development and flower organogenesis.These results showed that CsaV3₂G015930 is the main target gene related to the traits of multiple female flower in cucumber.3.The F₂ population was constructed by the tuberculate fruit moved up selfing line X1（P₁）and the tuberculate fruit moved down selfing lineX2（P₂）as the parents to identify the phenotype and analyze the genetic rules.Twenty plants with extreme phenotype of tuberculate fruit moved up and 20 plants with extreme phenotype of tuberculate fruit moved down were selected,and the tuberculate fruit moved up pool（Tu）,tuberculate fruit moved down pool（Td）and parent pool（Mp,Pp）were constructed for high-throughput sequencing（BSA-seq）.Combined with bioinformatics analysis,16 candidate genes related to cucumber tuberculate fruit position traits were predicted,including 4 SNP on chromosome 1 and 5,and 12 InDel on chromosome 1,4 and 5,respectively.According to the distribution of All-index on chromosome,it was inferred that CsaV3₁G030610,CsaV3₁G030630,CsaV3₁G029520 and CsaV3₁G030640 located on chromosome 1（5.840Mbp-18.376 Mbp）were the main target genes.In this study,it is speculated that the candidate gene CsaV3₁G030610,CsaV3₁G030630 located in the overlapping region of cucumber chromosome 1（5.840 Mbp-18.376 Mbp）is mainly involved in the formation of cell wall and is associated with fruit spines.It is speculated that it is related to the position and character of cucumber tuberculate fruit position.