Joseph Knoll and William F. Anderson, Crop Genetics and Breeding Research Unit, USDA-ARS, Tifton, GA
Sweet sorghum (Sorghum bicolor) has potential as a multi-purpose biofuel crop in the Southeast USA. The sugars from the juice can be easily fermented into ethanol or used to produce other chemicals, while the bagasse could be burned in boilers for energy or used for cellulosic ethanol. The grain and leaf portions could be utilized as livestock feed. The crop is more tolerant of heat and drought than corn (Zea mays), and requires less N fertilizer. Despite its advantages, all current cultivars are pure lines that produce little seed on very tall plants, which is a major limitation to development of a sweet sorghum-based biofuel industry. There is a need to develop hybrid seed production on short-statured seed parents. Hybrids should also be more productive than pure lines. A test was conducted at Tifton, GA to assess the potential for heterosis and combining ability in some of the currently-available sweet sorghum germplasm. A Design II mating design was constructed using three male-sterile (A-line) seed parents as females and 19 pollen parents as males to generate 57 hybrids. In 2012 all the hybrids, male parents, and the male-fertile (B-line) versions of the females were planted in a randomized complete block design with two replications. Each plot consisted of two rows. One row was used for sampling, while the other was harvested for total biomass at the end of the test. Over the course of the growing season, juice BRIX was sampled at regular intervals to monitor sugar production. At harvest, a sample of three stalks was taken from each plot, and these were separated into leaves, stalk, and panicle. The juice was extracted from the stalks with a roller mill and was quantified. Other traits measured included plant height, lodging score, and days to 50% anthesis.