| Watermelon(Citrullus lanatus) originated in the arid areas of southern Africa, and is now widely cultivated worldwide. China is the largest producer and consumer of watermelon, with a total annual production of approximately 70 million tons. Because of the economic and horticultural importance of this crop, there has been increasing interest in breeding programs to improve the fruit quality of watermelon plants. Using molecular linkage genetic maps and quantitative trait locus(QTL) mapping technology, it is possible to estimate the number of QTLs in the genome. The aim of the present study was to develop SNPs based on the high-throughput re-sequencing data of Garden female parent and LSW-177 and convert them into cleaved amplified polymorphic sequence(CAPS) markers. Then, we aimed to construct a genetic linkage map for watermelon using CAPS markers, and to map QTL associated with fruit length,fruit width, fruit shape index, fruit rind thickness, fruit weight, soluble solids content, fructose, sucrose and glucose. The main results were as follows:(1)Garden female parent and LSW-177 were showed highly significant differences(P< 0.01) in fruit shape,rind thickness, and sugar content and showed significant differences(P< 0.05) in fruit weight,means its suitable to construct a segregating population. All the traits showed a continuous distribution in RILs population, suggesting that they were controlled by multiple genes and appropriate to conducted QTL analysis.(2)Pearson correlations analysis for fruit length, fruit width, fruit shape index, fruit rind thickness and fruit weight showed that: fruit shape index showed a high significant positive correlation with fruit length and showed a high significant negative correlation with fruit width; fruit rind thickness had high significant positive correlation with fruit length and width; fruit weight showed a high significant positive correlation with fruit length, width and fruit rind thickness, but showed a high significant negative correlation with fruitshape index. Pearson correlations analysis of sugar content indicated that soluble solids content had significant positive correlation with fructose, sucrose and glucose. Fructose had high significant positive correlation with sucrose and glucose, while sucrose showed a high significant negative correlation with glucose.(3)We developed 352,483 SNPs which were showed polymorphism in parents by bioinformatic analysis for re-sequencing data. In this study, we developed 524 CAPS markerstotally and 278 markers showed polymorphism between parents, the polymorphism rate is 53.1%. We markered F2S7 generation with 125 families using 278 CAPS markers and constructed a genetic map.The map contained 246 markers and grouped on 11 linkage groups, spanning a total length of 2423.8cM, with an average of 9.9 c M between markers.(4)A total of 27 QTLs for 9 traits were located using the composite interval mapping(CIM) method with Windows QTL Cartographer 2.5 software. Eleven QTLs for fruit shape were mainly located on linkage group 3 and 8 with contribution rate range from 4.46% to 71.41%; Four QTLs for fruit rind thickness were located on linkage group 3、7 and 10 with contribution rate range from 7.19% to 18.86%; Three QTL related for fruit weight were located on linkage group 3 and 8 with contribution rate range from 6.73% to 16.34%; Four QTLs for soluble solids content were located on linkage group2、6 and 9 with contribution rate range from 8.60% to 32.10%; Five QTLs for fruit soluble sugar content were identified totally, these QTLs were located on linkage group2、6、7 and 9, with a contribution rate rang from 8.79% to 24.10%.In this study, we constructed a genetic linkage map using CAPS molecular markers which were developed based on high re-sequencing data. By QTL analysis for fruit-related traits, we located 27 QTLs totally, these will be useful for molecular marker-assisted selection breeding in watermelon. |
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