Evaluation of sweet sorghum varieties for multi-purpose utilisation in Kenya

Sweet sorghums (Sorghum bicolor L. Moench) are sorghum varieties that accumulate high levels of sucrose in the parenchyma juicy stems. Sweet sorghum (SS) is a multifunctional crop. It that can be cultivated for simultaneous production of grain for food or feed, and utilisation of juice from stalk in production of value-added products like syrup and ethanol. The aim of this study was to undertake agronomic screening of imported sweet sorghum cultivars for possible adoption in Kenya. Twenty five sweet sorghum varieties were sourced from ICRISAT, Nairobi office and compared with 20 varieties sourced from the Brazilian Agricultural Research Corporation (Embrapa). The varieties were planted during both the short and long rain seasons of 2012 at the JKUAT research farm in a completely randomized block design) with three replications. Each plot consisted of four rows, 5 m long and 3 m wide (15m²), the spacing was 75cm by 30 cm and cultural practices such as weeding and disease control were done to assume optimum stalk and sugar yields. The Brazilian varieties were significantly superior to the ICRISAT varieties in terms of height (2.8m± 0.4 versus 1.8m ±0.3), diameter (37 cm±5 versus 21± 4) and juice sugar content (°Brix 22± 3 versus 17.5 ±4). However, some of the Embrapa varieties were short (height of 1.4m±0.2) and thin (diameter of 12 cm±2) including Rio, Ramada, Rema, Theis, wiley and Wray. The ICRISAT variety IESV 91018LT had the highest sucrose concentration of 72.77 g l-1 followed by RIO from Embrapa at 40.86 g l-1. Wiley had the highest fructose and glucose content at 16 g l-1 ±1.4. Rio and CMSXS S636 of Embrapa had the highest sucrose purity at 83%±3. Due to high content of non reducing sugar (sucrose) the RIO can be ideal for syrup production whereas the CMSXS series would be ideal for bioethanol production due to their high content of fermentable reducing sugars’(glucose and fructose). However the ICRISAT varieties IESV 91018LT and IESV 92008DL possess both reducing and non reducing sugars and hence would be ideal for multipurpose utilization.