Grain Quality Analysis of a Diverse Collection in Sorghum.

Sorghum grain quality traits involve kernel size, weight and protein content. They are complex quantitative traits, which influence the nutritional and functional properties of sorghum and determine the grain value to producers and consumers. Association mapping, also named linkage disequilibrium (LD) mapping, is an effective and efficient method to establish marker-trait relationships for grain quality traits. As a self-pollinated species with an outcrossing rate of 6%, , sorghum has relatively low sequence diversity and moderately extensive LD, compared to other outcrossing species, which can benefit candidate gene association mapping with single nucleotide polymorphism markers (SNP). Our research is to identify SNP markers from candidate genes associated with sorghum grain quality traits. Two replications of a 300-line sorghum diversity panel which captures a wide range of genetic diversity in global sorghum germplasm were planted and harvested separately in KS and IN, 2007. Till now, 580 samples have been measured by the High-throughput Single Kernel Characterization System (SKCS). Hardness index values have a maximum of 126.5 and minimum of 3.4. The weight of Kernel ranges from 15.1 to 45.4mg, while the diameter of kernel ranges from 0.7 to 3.2mm. The average values of the three parameters are respectively 77.7, 23.0 mg, and 1.6mm. This result proves the diversity of the sorghum panel and provides a good fundament for association mapping. Two wet chemistry method, pepsin digestion and small scale fermentation assays, will be conducted on selected samples to predict protein digestibility and fermentable sugar in sorghum. Calibrated Near-Infrared Spectroscopy (NIR) will be employed to obtain compositional attribute as protein, moisture content for the remaining samples. By now, more than 15 candidate genes in sorghum starch metabolism pathway have already been sequenced. SNP identified in more grain quality candidate genes will be genotyped across the 300 diversity sorghum lines using Illumina Golden Gate Assay. Then a unified mixed-model method will be performed to carry out association analysis between the candidate SNP and the grain quality phenotypic traits.