QTL Mapping For Sugar Content Of Stalk Juice In Sweet Sorghum

Particular varieties of Sorghum bicolor (L.) Moench, known as'sweet sorghums' or 'sorgos', accumulate 10-25% sugar in expressed stalk juice near the time of grain maturity. Sweet sorghums are generally characterized by wide adaptability, drought tolerance, waterlogging tolerance, saline-alkali tolerance, rapid growth and high biomass.High sugar content of sorghum stalk is an important factor in the sorghum silage production. Sweet sorghum is also considered a potentially valuable source for biofuel production. Thus, increasing stem sugar yields is becoming an important objective in sweet sorghum breeding.To identify the genomic regions controlling sugar content and to develop molecular markers linked to sugar content in sweet sorghum, we used an F6 segregating population consisting of 174 individuals derived from a cross between a normal inbred line,654, and a high sugar content inbred line, LTR108, for genetic linkage mapping and quantitative trait locus (QTL) analysis. The main results are as follows:1. We constructed a genetic linkage map spanning 1686.9 cM based on a total of 270 simple sequence repeat (SSR) markers, and the average distance of loci was 6.25cM.2. The content of 654 and LTR108 contributed to the 174 lines population was about 0.497 and 0.503, respectively. The distribution of genotypic composition of the population fitted well. The skewness of the 11 traits was -0.92-1.19 estimated from the data of the families. In a word, the population was suit to genetic mapping and QTL mapping. 3. QTLs were identified for all 11 traits and were generally co-located to 7 locations (LG-1, LG-2, LG-6, LG-7, LG-9 and LG-10). Five QTL alleles from LTR108 were detected for increased Brix on LG-3, LG-6 and LG-7 in 2008 and 2009, respectively. These five QTLs account for 6%,13%,14%,11% and 13% of phenotypic variance.654 also contributed QTL alleles for increased Brix on LG-8 in 2008. Two QTL alleles accounting for 11% of phenotypic variance from LTR108 were found for increased Heading date on LG-2 and LG-6, respectively. A major height QTL from 654 for decreasing height, dw3, was identified on LG-7 in both 2008 and 2009. Interestingly, QTLs for decreasing mean internode length were identified on the same location with dw3 in both two years.