Variation in starch genes explain differences in phenotypic properties in sorghum

Sorghum is an important grain exploited for a wide variety of uses in the food, animal feed and bioprocessing industries. In this study the chemical composition of the seed starch, protein, fat and fibre content, and also phenotypic traits including gelatinisation temperature, peak viscosity, breakdown and setback were investigated in 55 accessions from the USDA-ARS germplasm collection. This study also used a sequencing approach to detect DNA base changes in the three important starch synthesis genes; soluble starch synthase (SSIIa), granule bound starch synthase (GBSS) and starch branching enzyme (SBEIIb) in the 55 accessions. It investigated whether there is a genetic basis to different phenotypic traits such as gelatinization temperature in sorghum. Tassel software was utilised to merge the genotypic and phenotypic data, form statistical association for the dissection of complex genetic traits, and attempt to find QTLs. Our results found a wide variation for all parameters measured and in all genes studied. Of particular interest were three SNPs in the SSIIa gene which could distinguish four distinct sorghum haplotypes, which also had significant differences in the relative composition of starch, fat, fibre and protein in the seed. Haplotypes 1 and 2 had low gelatinisation temperature of 80.7oC and 83.7 oC, respectively, whilst Haplotypes 3 and 4 had significantly higher gelatinisation temperature of 92.8 oC and 88.8 oC respectively. This information may subsequently be used to develop molecular markers which could be used in breeding programs developing germplasm for different end uses in the food, animal feed and bioprocessing.