Tapping the US Sweet Sorghum Collection to Identify Biofuel Germplasm.

The narrow genetic base in sweet sorghum [Sorghum bicolor (L.) Moench] breeding programs is limiting the development of new varieties for biofuel production.  Therefore, the identification of genetically diverse sweet sorghum germplasm in the U.S. National Plant Germplasm System (NPGS) collection is imperative for biofuel breeding programs as biofuel production expands to new regions. Nine-hundred twenty-five sweet sorghum accessions from the NPGS collection were agronomically evaluated and a subset of 56 accessions selected for further evaluation. A 2-year replicated trial of this subset together with 17 U.S. sweet sorghum varieties were evaluated for agronomic and biofuel traits [flowering time, plant height, fresh and dry weight, brix, juice volume, percent of moisture, and fermentable sugars [dinitrosalicylic method (DNS)] and disease response [anthracnose (Colletotricum sublineolum) and rust (Purcina purpurea)].  Nine accessions from the NPGS collection originally from South Africa, Ethiopia, Sudan, Zimbabwe, and the U.S. showed brix values ranging from 10 to 14, with  five accessions  having a higher amount of fermentable sugars than U.S. references accessions (DNS = 9.86 to 11.42). Likewise, the total dry matter content of three accessions originally from Ethiopia and U.S. were higher than the U.S. reference accessions (>156.87 g/plant).  Multiple new sources of anthracnose and rust resistance were identified; being PI 156424 from Tanzania resistant to both diseases. The results demonstrated that accessions in the NPGS sorghum collection enclose valuable genes/alleles for biofuel traits that are not being used in U.S. biofuel breeding programs. Thus, the integration of these accessions into these programs will aid to increase genetic diversity and development of new biofuel varieties.