| Siraitia grosvenorii (Swingle) C. Jeffrey (Cucurbitaceae family), a dioecious, perennial and liana plant with root tubers, is an economically important species endemic to southern China, with the most planting in Guilin. It is a highly heterozygous diploid species with a chromosome number of 2n=28. The fruits of Siraitia grosvenorii, called "Luohanguo" have long been used as a food and beverage material as well as a traditional Chinese medicine. The pharmacological characteristics of Luohanguo make it a pulmonary demulcent and emollient for the treatment of dry cough, sore throat, dire thirst and constipation. The fruit contains zero-calorie high intensive natural sweeteners known as mogrosides, a group of terpene glycosides. Among these, the mogrosides v is about 300 times sweeter than sucrose and pharmacological effects have been known, and have been produced on an industrial scale. As such, Luohanguo has been used as a sugar substitute for patients with adiposity and diabetes.The first genetic linkage map of Luohanguo (Siraitia grosvenorii [Swingle] C. Jeffrey) was constructed with 150 F1 individuals derived from a cross between the cultivars Yehong 1 and Changtanguo using inter-simple sequence repeat (ISSR) and sequence related amplified polymorphism (SRAP) markers, and the QTL of ten agronomic traits was analyzed for the first time. The main conclusions are as follows:1. The first F1 mapping population of Luohanguo was constructed. The population consisted of 150 F1 progenies derived from a cross between the wild species Hongmaoyihao and cultivar Changtanguo performed at Xing’an County, Guilin City, Guangxi Province, for genetic map construction and QTLs analysis of ten agronomic traits.2. Out of 100 ISSR primers examined, only 17 (17%) of the ISSR primers were selected for efficient amplification and detection of polymorphism between the two parents and 150 F1 progenies. They produced 51 ISSR markers. The average number of markers produced per primer was 3. Fragment sizes ranged from 200 to 2,000bp. A total of 196 SRAP primer combinations were used to screen for polymorphisms between parents and 74 primer combinations showed polymorphisms.The 74 primer pairs yielded 222 polymorphic loci with an average of 3.07 polymorphic loci, and 122 primer pairs produced no polymorphic loci. In addition, we investigated five qualitative traits for genetic map construction.3. The genetic map of Luohanguo (Siraitia grosvenorii [Swingle] C. Jeffrey) was constructed using 278 polymorphic loci(51 ISSR and 222 SRAP polymorphic loci and 5 qualitative traits). Among the 278 markers obtained,203 markers (29 ISSRs,173 SRAPs and 1 sex marker) were mapped to 27 linkage groups. The map covered 1474.1 cM with an average map distance of 7.3 cM between adjacent markers and a maximum map distance of 52.6 cM between two markers. The markers distributed randomly in 27 groups except for minor clusters in the distal region of LG2. All 27 linkage groups consisted of 2-36 loci ranging in length from 19.5 to 152.6 cM and accounted for 65.2% of the total map distance.4. Composite interval mapping method of Windows QTL cartographer V2.5 was employed in QTL analysis of ten agronomical traits including stem diameter, petiole length, leaf width, leaf length, chlorophyll content, fruit fresh weight, fruit width, fruit length, fruit index and leaf total nitrogen content in Siraitia grosvenorii. A total of thirty-three QTLs were mapped on thirteen linkage groups for the ten triats with LOD≧ 2.5. Phenotypic variation explained by the single putative QTL varied from 8.40% to 32.95%, and the LOD score ranged from 2.60 to 7.40. These QTL included one for stem diameter,four for petiole length,five for leaf width, four for leaf length, three for chlorophyll content, three for fruit fresh weight, three for fruit width, five for fruit length,two for fruit index and three for leaf total nitrogen content. |
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