Construction Of A Genetic Linkage Map And QTL Analysis Of The Anti-CMV Trait In Cucumber (Cucumis Sativus L.)

Cucumber mosaic virus (Cucumber mosaic virus, CMV) is the main factor leading to the cucumber virus disease. It can cause fruit malformation, loss of commodity or even never produced. So anti-CMV breeding of cucumber becomes one of main targets of disease-resistant breeding for cucumber. The technology of the real-time quantitative PCR is high automation, more specific, and can effectively solve the PCR pollution. The technology can be used to test the relative content of the gene expression level of the CMV replicase gene accurately, agilely and rapidly. Molecular markers can be used to build genetic maps, and then QTL location, scanning quantitative trait loci, analysis of the contribution rate of the traits can be done by relevant software. The molecular markers linked to QTL can be in breeding pairs of the QTL on the genetic dynamics track, which can greatly enhance the accuracy and predictability of the breeding selection on the genotypes of quantitative traits. In this study, F-3, a CMV-resistant inbred line in Cucumber, HZL04-1 a CMV-susceptible inbred line, and their hybrid F₂ progenies were provided by Tianjin KERUN Cucumber Institute. SSR and SCAR molecular markers were applied in the construction of the genetic linkage map. Joinmap 3.0 software was used to construct the map; the anti-CMV trait was located on this linkage map by QTL mapper 4.0. The main results of this study were as follows:1. The resistance to CMV of progeny population of F1,BC1 and F2 were evaluated at seedling stage, the result showned that the resistance to CMV was determined by nuclear gene and were controlled by three genes.2. The relative content of the expression of CMV replicase gene in cucumber was measured by the SYBR Green I real-time fluorescence quantitative PCR. By the preliminary analysis of the relative expression levels of CMV replicase gene, the result was that the relative expression of the CMV replicase gene in the 22 F2 plants was very few, and the 22 plants were CMV-resistant.3. 170 SSR polymorphic locus, 3 SCAR polymorphic locus and 7 EST-SSR polymorphic locus were obtained. A molecular genetic linkage map including 7 linkage groups and containing 170 SSR markers, 3 SCAR markers, 6 EST-SSR markers was obtained by Joinmap 3.0. This map covering the cumcumber genome was 862.886cM; the average distance between two markers was 4.79cM. The number of tags for each linkage group was between 18 and 40, and the length for each linkage group was between 82.684cM and 167.757cM.4. The correspondences between the 7 linkage groups and the chromosomes were that the first linkage group– the third chromosome, the second linkage group– the second chromosome, the third linkage group– the seventh chromosome, the fourth linkage group– the fourth linkage group, the fifth linkage group– the sixth chromosome, the sixth linkage group– the fifth chromosome, the seventh linkage group– the first chromosome.5. The QTL of the anti-CMV trait was mapped by Composite interval mapping in QTL mapper 4.0 and 17 controlling CMV resistance QTL loci were detected, which were named cmv1-17. The cmv1 located on chromosome 3, cmv2 cmv7 located on chromosome 4, cmv8 cmv14 located on chromosome 6, cmv15 cmv17 located on chromosome 5.6. The cmv17 showed synergistic positive additive effect and the variation rate could be explained was 67.3%. It was indicates that the loci was a primary locus controlling the resistance to CMV.7. SCARcmv-200, the flanking marker of cmv17, was just the SCAR maker linked cucumber anti-CMV and was obtained by the use of BSA method, and the distance between cmv17 loci and SCARcmv-200 was only 0.5cM. It was confirmed that the loci cmv17 was the main loci for controlling the resistance to CMV. The SCARcmv-200 and the major gene of controlling the resistance to CMV were closely linked.