Biochemical evaluations of Ethiopian sweet sorghum [Sorghum bicolor (L.) Moench] accessions for sugar production

Sweet sorghum [Sorghum bicolor (L.) Moench] is one of the varieties of sorghum having stalk with high concentration of soluble sugar. Biochemical evaluations of sweet sorghum enable it to determine the potential of the crop to be utilized for sugar production at industrial level. This study was designed to evaluate the Ethiopian sweet sorghum germplasms for production of crystalized sugar. In this study, 91 sweet sorghum accessions were evaluated based on total soluble sugar content. As a result, 8 accessions having high total soluble sugar scores were selected and evaluated for further biochemical quality traits. In addition, three agronomic parameters were used to evaluate their effect on the biochemical features of the studied sweet sorghum and sugarcane accessions. These traits include total soluble sugar (degree brix), polarization, sucrose content, sugar purity, days to maturity, stem height and stalk diameter. Three high quality sugarcane (Saccharum officinarum) genotypes collected from Kessem sugar industry of Ethiopia were used as standard checks. Analysis of variance (ANOVA); mean separation and correlation were analyzed using R-software. ANOVA revealed significant variations for polarization value and purity of sweet sorghum juice at p ≤ 0.001. The mean separation analysis revealed that maximum and minimum degree brix were obtained from T-11 (20.23%) and T-28 (16.88%), respectively. In the present study, the polarization values ranged from 41.57 (T-28) to 69.30 ⁰Z (C-86/12).The three sugarcane standard cheeks showed relatively higher values of polarization in comparison with the sweet sorghum accessions. Among the sweet sorghum accessions, T-13 showed relatively higher polarization value whereas the remaining sweet sorghum accessions didn't show significant variation. The average sucrose content (pol percentage) was ranged from 11.98% (T-28) to 16.77% (C-86/12). C-86/12 sugarcane accession showed the highest (16.77%) mean value for sucrose content whereas T-28 sweet sorghum accession scored the lowest sucrose content (11.98%). Maximum purity of sugar was recorded from SP-70 (90.77%) sugarcane accession whereas; the minimum value was recorded from T-11 (63.62%) sweet sorghum accession. In addition, the correlation analysis revealed that there were both positive and negative correlation among biochemical and agro morphological traits of sweet sorghum and sugarcane. Brix value showed positive correlation with polarization (0.56**) and sucrose content (0.71**) while it was negatively correlated with sugar purity (-0.06), days to maturity (-0.06), stem height (-0.19) and stalk diameter (-0.16). On the other hand, polarization showed strong positive correlation with sucrose content (0.95**), purity (0.76**) and days to maturity (0.78**). In comparison with sugarcane, the studied sweet sorghum accessions revealed quite lower performance in polarization, sucrose content and purity. Nevertheless, this study confirmed the existence of a climate smart and promising sweet sorghum genotypes used for the production of sugar and syrup as an alternative sweetener.