Abstract: 【Objective】The purpose of this study is to construct a molecular genetic map and map the QTL of the fruit-associated traits with CAPS and SSR markers in watermelon, which will provide a theoretical basis for traits improving, gene fine mapping and gene cloning.【Method】Fruits of female parent PI186490, male parent LSW-177 and F2 population derived from the cross between the two watermelon strains were picked in 40 days after pollination. Fruit shape index, center and edge brix, center and edge flesh firmness, rind hardness, seed length, seed width, seed thickness and 100-seed-weight were investigated correspondingly, then the obtained data were analyzed by SPSS19. Both parent materials genomes were resequenced by Illumina HiSeq 2000 platform for high-throughput sequencing, outputed 10G each data sample, covered more than 20× of watermelon genome. With the published genome as a reference, the obtained data were assembled with bwa, and explored for the SNP by Samtools. The sequence 1 000 bp around the SNP loci was extracted by self perl script and then inputed into SNP2CAPS to transform into CAPS markers. Twenty CAPS restriction sites were selected evenly on the 11 chromosomes. CAPS primers were designed 100-500bp around the mutation by Primer Premier 5 for PCR amplification and digestion detection. 1% agarose gel electrophoresis was used to detect the digestion products. SSR markers in this experiment were come from the published literature. The products of SSR-PCR were detected by polyacrylamid gel electrophoresis. All the molecular data were tested by chi-square. Markers which were confirmed the proportion 1﹕2﹕1 were chosen for the genetic linkage map. The genetic linkage map was constructed by Mapmaker/Exp version 3.0. The markers were grouped with the order ‘Group’. The number of the markers in the group which was less than 8 was sequenced faultlessly with the order ‘Compare’, which was more than 8 was ordered with the order ‘Try’. Map Chart 2.1 was used for drawing this genetic linkage map. QTL Network 2.0 was used for QTL analysis. 1 000 times repeats were done with the replacement testing, the critical threshold was P=0.005, and the method of constructing the map was composite interval mapping. The whole genome was scanned on every chromosome with 1 cM walking speed. QTL additive effect and epistatic effect were analyzed by the software.【Result】This genetic linkage map contained 16 linkage groups and included 87 CAPS markers and SSR markers. The map was 1 484.3 cM and the average distance between two makers was 15.46 cM. Mapping the QTL of the fruit-associated traits and analyzed by software QTL Network 2.0, and a total of 8 additive QTL and one pair of epistatic QTL were detected. Among the additive loci, 1 is for fruit shape index(QFSI 1), 1 for center brix (QCBR), 1 for center flesh firmness(QCFF), 1 for edge flesh firmness(QEFF), 1 for seed length(QSL), and 3 for seed width(QSWD 1, QSWD 2, QSWD 3). The epistatic loci, FSI 2 and FSI 3 are for fruit shape index. Phenotypic contribution rate of 10% or more have six QTL, which explained 11.7% -18.8% of the genetic variation. All of the QTL explained 7.12%-18.8% of the phenotypic variation.【Conclusion】A molecular genetic linkage map composed mainly of CAPS markers was constructed. Eight additive QTL and one pair of epistatic QTL, which control the fruit-associated traits of watermelon were located, thus providing a scientific basis for further fine positioning and cloning the genes controlling superior traits of fruit of watermelon.

Key words: watermelon , genetic linkage map , CAPS , QTL