Stalk strength and sugar content of 55 dual-purpose sorghum inbreds

In 2012, sorghum was approved by the U.S. Environmental Protection Agency (EPA) as an "advanced" bioenergy feedstock in cases where both the grain and stover are both used for energy production (USEPA, 2012). It is desirable, therefore, to develop taller varieties of sorghum to increase biomass yields. However the taller the plant gets, the more susceptible it becomes to lodging, reducing grain yield in the end. Additionally the ability to characterize the storage stability of new sorghum varieties in terms of moisture content and free sugars content is advantageous. In this study, high throughput assays to characterize stalk strength based on rind penetrometer resistance (RPR) and sugar content based on an enzymatic assay of new varieties of sorghum were demonstrated. RPR measurements and estimates of glucose and sucrose contents of the leaves and the stalks were conducted on 40 dwarf grain sorghum inbreds and 15 photoperiod sensitive sorghum inbreds. Results showed stalk strengths of dwarf grain sorghum ranged from 2.43 to 7.72 kgf while those of photoperiod sensitive sorghum ranged from 2.72 to 10.50 kgf. Dwarf grain sorghum contained 0.1% to 6.9% and 0.3% to 3% glucose in stalks and leaves; 0 to 15% and 0 to 6.5% sucrose in stalks and leaves, respectively. Photoperiod sensitive sorghum contained 0.6% to 12% and 0.3 to 1.7% glucose in stalks and leaves, while sucrose levels in stalks and leaves were 0.3% to 17% and 0 to 3.1%, respectively. These results provide a framework for stalk quality assessment in selecting inbreds with stronger and higher free sugar content.