| Watermelon (Citrullus lanatus;2n=2x=22) is a kind of annual herb which can be subjected to the Cucurbitaceae. Watermelon is also one of the most important fruit vegetable in the world. The sugar content in watermelon is one of the most important traits in watermelon quality measurement.High sugar content watermelon can satisfy most watermelon quality traits for most people’s requirements. In the other hand, Low sugar content watermelon with good flavor can also have significance for diabetic patients and satisfy their special requirements. Therefore, research of sugar content in watermelon is very important:firstly, it can be very useful to the watermelon breeding when we have the distinguish inheritance; secondly, using the method of molecular markers to obtain the markers which associated with the sugar content in watermelon can provide theoretical basis for the further research in molecular marker-assisted selection. This experiment used the method of molecular biology to construct the genetic linkage map for watermelon and found the SSR markers which tightly link with the sugar content in watermelon, analyzed the QTLs. These SSR markers linked to QTLs could provid the reference data of genes localization and sugar content genes isolation in watermelon.In this experiment, we used the high sugar content watermelon inbred line Garden Female Parent which origins from China as the female parent. And low sugar content watermelon inbred line LSW-177which origins from U.S as the male parent. LSW-177is offered by Doctor Angela R. Davis who works in the South Central Agricultural Research Laboratory, Agriculture Research Service, US Department of Agriculture. The six generations and180F2population were derived from Garden Female Parent and LSW-177. The content of fructose, glucose, sucrose both in middle part and edge part have been measured respectively. And we also defined the three kinds of sugars’ summation as the total sugar content. The inheritance and sugar content related QTLs were analyzed.The analysis showed that, the content of fructose, glucose, sucrose and total sugar of F2showed continuous variation from the lowest to the highest according with normal distribution. The results exhibited an obviously characteristics of quantitative character inheritance, controlling by the poly-gene. The inheritance of fructose and glucose accord with the major gene plus poly-gene. The F2population separation of sucrose has segregation distortion in some extent. The sugar content in middle part is higher than the edge part, and both the tow parts have the same inheritance tendency. According to the correlation analysis of the content of fructose, glucose, sucrose with total sugar we can get the results that, glucose>fructose>sucrose. So the content of glucose has the biggest relation with the total sugar content. And both of the middle part and the edge part have the same result.Using the method of SSR molecular markers, we obtained55paris of polymorphism primers through355paris of watermelon SSR markers and melon SSR markers with the two parents. The rate of polymorphism in watermelon SSR markers is10.14%while in melon SSR markers is only1.56%. To analyze the F2population using the55paris of polymorphism primers, a genetic map with45SSR markers and13linkage groups was developed, which spanning547.3cM with a mean marker interval of1244cM.2QTLs associated with sugar content were detected both in middle and edge part. The2QTLs distributed in3,12linkage groups respectively, and they were all additive effects. Their LOD values were3.1,3.29. The2QTLs were able to explain6.56%,7.09%of total phenotypic variation.4SSR markers(MU8184-3、MCPI-12、TJ116、 MU8558-3) were detected which associated with the total sugar content in watermelon. These SSR markers linked to QTL could be provided the reference data of genes location and sugar content genes cloning in watermelon. |
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