Genetic Analysis And Identification Of QTLs For Resistance To Cucumber Mosaic Virus In Pepper(Capsicum Annuum L.)

Cucumber mosaic virus (Cucumber mosaic virus, CMV) is the main virus type leading to the virus disease on pepper. This disease affects both yield and quality in pepper production. The symptoms in field mailnly show malformation of fruits, loss of commodity or even never produced. In order to overcome the damage of CMV disease, breeding cultivars with CMV resistance is becoming one of main targets in pepper breeding.For CMV-resistance breeding on pepper, we should understand the subgroup of CMV infecting pepper plant. The technology of the real-time quantitative PCR can be used to identify the subgroup of CMV in plant more rapidly and accurately. The utilization of molecular markers can be used to build genetic maps of pepper, and the quantitative trait loci relative to CMV-resistance also can be scanned by QTL analysis softwear. With the help of the molecular markers linked to CMV-resistance QTL, the accuracy and foreseeability for breeding selection on genetype of quantitative trait will be improved, and the efficiency for breeding on pepper is also increased.In this study, the subgroup and strain of CMV infecting pepper plant in Hubei province was identified firstly. Secondly, we screened the optimal condition of seedlings inoculation identification for pepper CMV disease and we also evaluated the CMV resistance of germplasm resources on pepper. Thirdly, two inbred lines of the pepper varieties, a CMV-resistance homozygous P0747and a CMV-susceptible line P0630, and their segregation populations were developed. Both parents and their segregation populations were used for inheritance analysis and genetic map construction. Finally, the QTLs relation to CMV-resistance was located by CIM method. The results of QTLs analysis will guide the CMV-resistance breeding on pepper.(1) Using the RT-PCR method and primers designed from the sequence of CP genes, the CMV isolates in Hubei area was identified. The results were as follows:the CP genes of CMV isolates in Hubei area shared98.2%-99.2%homology with those of CMV subgroup IB strains from Genbank. It was determined that all of the CMV isolates belonged to the subgroup IB of CMV.(2) The optimal condition of seedlings inoculation identification for pepper CMV disease is as following:The youth test peppers at4leaf-stages were dusted with600-mesh carborundum and inoculated by rubbing the leaves with inoculums. After inoculation, pepper seedlings were kept in a plastic house maintained at25℃to30℃. Totally seventy-four inbred lines were identified for CMV-resistance, and2inbred lines were resistant to CMV,26inbred lines moderate resistant.(3) Genetic analysis on the resistance of CMV by Griffing’s complete diallel crosses. The results of the analysis cleared the principle of parent choice in cross breeding of disease-resistance. The two parental lines and their segregation populations obtained from a cross between them were used for inheritance analysis by the joint segregation analysis method. Our results revealed that CMV resistance in’P0747’is controlled by two partially additive-dominant major genes and additive-dominance polygenes and the polygenes effect existed at the same time.(4) A F2population was used for constructing linkage groups by SSR and ISSR methods. This map included140markers mapping onto17LGs, covering1420.5cM according to the Kosambi function. The average distance between the markers was10.1cM.(5) QTLs were detected by the composite interval mapping (CIM) method based on the linkage groups. A total of six QTLs, qcmv.hb-4.1, qcmv.hb-7.1, qcmv.hb-8.1, qcmv.hb-8.2, qcmv.hb-8.3and qcmv.hb-16.1, were identified on4LGs (LG4, LG7, LG8and LG16) in two inoculation experiments in2009, which accounted for2.8-43.5%of the individual phenotypic variations. Notably, the QTL qcmv.hb-8.2was repeatedly identified in two seasons and showed the largest effect and explained37.7-43.5%of the total phenotypic variation, with the allele from’P0747’increasing CMV resistance by0.59-0.64. The QTL qcmv.hb-4.1also had a sizable effect and could explain11.2%of the variation in summer and10.7%of the variation in autumn, with the allele from’P0747’ increasing CMV resistance by0.24-0.25.