Sweet Sorghum Heterosis.

Sweet sorghum (Sorghum bicolor) has potential to be used as a bioenergy feedstock.  Sweet sorghum cultivars are characterized by the accumulation of large juice volumes with high brix concentrations.    These sorghums can be harvested, milled, and fermented to ethanol using the same technology used to process sugarcane. 
Traditionally, sweet sorghum is grown as a cultivar.  However, these cultivars produce very little seed and are too tall to harvest efficiently. The development of sweet sorghum hybrids, produced on grain-type females with high sugar concentrations is one way to overcome this limitation.   Our program has developed these types of lines and is now evaluating them in hybrid combinations.  We have characterized the first generation of sweet sorghum hybrids produced using a sweet, grain-type female parent.  In three locations across Texas in 2007, mean brix content of the top ten percent of sweet sorghum hybrids tested was 13.09 percent, mean sugar yield was 1.54 tons per acre, and mean biomass production was 53.34 tons per acre fresh weight.  These hybrids produce yields comparable to the six varieties tested that had a higher mean brix content of 15.17 percent, but a lower mean sugar yield of 1.32 tons per acre, and mean biomass production of 38.32 tons per acre fresh weight. 
High parent heterosis for brix concentration ranged from -24.61% to 7.39%.  Only 13% of hybrids had higher brix than their parental lines.  Heterosis ranged from -54.80% to 81.28% for sugar yield per acre and from -27.97% to 43.38% for fresh biomass production per acre.  Sugar yield and fresh biomass yield are highly correlated (r²=0.86).  42% of sweet sorghum hybrids produced more sugar per acre than their parents and 58% of hybrids produced more fresh biomass than either parent.