Genome-Wide Association Study For Main Sugars And Organic Acids In Tomato Fruit

The concentration of sugars and organic acids is a key index impacting tomato(Lycopersicon esculentum Miller.) fruit quality. In the long tomato breeding processess, the total sugars in tomato were evaluated by soluble solid content and the concentration of organic acids were evaluated by titratable acid. Tomato fruit sugars and organic acids are typical quantitative traits controlled by series of quantitative trait loci(QTL). QTL researches focused on the main sugars and organic acids components are quite limited. In this study, we selected 174 tomato accessions with diverfied phenotypes and evaluated the main sugars and organic acids in tomato fruits at the red-ripe stage via Gas Chromatography-Mass Spectrometer(GC-MS). Genetic diversity, population structure and linkage disequilibrum were evaluated via 182 SSR markers with a whole genome-wide coverage. Genome-wide association study was conducted between the 182 SSRs and the main sugars and organic acids in tomato fruits. The main results are as follows:1. The main tomato fruit sugars and organic acids of 174 tomato accessions with diversified phenotypes were measured via GC-MS. 17 sugars and organic acids were detected in total, with eight sugars and nine organic acids. The main sugars are glucose, fructose,sucrose and galactose, etc. The main organic acids are malic acid, citric acid, butanedioic acid,butanoic acid, proline, etc. High correlations were observed between main sugars and organic acids and the highest correlation was observed between glucose and galactose. Significant negative correlations were detected between fructose, glucose and malic acid, glutamic acid.Complex correlation relationships were observed between main sugars and organic acids and other fruit quality traits.2. The population structure and linkage disequilibrium(LD) of the 174 tomato accessions were evaluated via 182 SSR markers. The population structure revealed that this whole 174 tomato accessions could be subdivided into two groups, including the cherry tomato group and the large-fruit tomato gruop. The LD was also evaluated via 182 SSR molecular markers and the population decayed at around 8 c M, indicating that positive associations could be detected with relative limited markers in this populations.3. Genome-wide associations study was conducted on the detected 17 main sugars and organic acids in tomato fruits using the mixed linear model(MLM). In total, 139 significantassociations(P<0.005), with 97, 83 associations in 2013 and 2014, respectively. We detected at least one significant association for 16 sugars and organic acids, except for threitol.Our result confirmed some reported QTLs or genes, such as fru9.1/PV, suc9.1/PV, ca2.1/HS,ca3.1/PV, ca4.1/PV, ca8.1/PV and Solyc06g072930.2. This study laid the foundation for identifying the key genes responsible for the metabolic and regulatory genes for tomato sugars and caids and had deep significance for tomato sugar and organic acid quality breeding.