Date of Award

Summer 2014

Degree Type


Degree Name

Master of Science (MS)

First Advisor

Mitch Tuinstra

Committee Chair

Mitch Tuinstra

Committee Member 1

Jeff Volenec

Committee Member 2

Mike Mickelbart


Sorghum is the fifth most important grain crop in the world. It is a staple food, feed, and silage crop in many developing countries in the semi-arid tropics. One factor that can impact sorghum forage quality is dhurrin content. Dhurrin is a cyanogenic glucoside naturally produced in the plant. When tissues containing dhurrin are crushed, hydrogen cyanide (HCN) is released during dhurrin decomposition. HCN is toxic to humans and livestock. While there is natural genetic diversity for the concentration of dhurrin within sorghum lines, there have been no naturally occurring dhurrin-free genotypes identified to date. ^ We have identified ethyl methanesulfonate (EMS) mutant sorghum lines that have disruptions in the biosynthetic and catabolic pathways of dhurrin metabolism. The first objective of this research was to determine the causal mutation leading to the acyanogenic phenotype of EMS 2447 and EMS 5085. Using Next-Gen sequencing and SNP marker analysis, we determined that a C493Y mutation in the biosynthetic enzyme CYP79A1 was the cause of the disruption in dhurrin production. Previous studies have shown that sorghum plants with a mutation in this gene had slower seedling growth compared to wild-type plants. Our second objective was to test whether lack of dhurrin production had any negative impacts on sorghum growth and development, as well as stay-green capacity. We designed an experiment to test the effects of the C493Y mutation using mutant and non-mutant plants from segregating F2families. Plots were planted in the summer of 2013. Plants were tested with the Feigl-Anger assay to determine the wild-type or acyanogenic phenotype of the F2s. Throughout the growing season, samples were collected to determine differences in growth, including: chlorophyll content index (CCI), plant height, leaf number, biomass, grain yield, and harvest index. We discovered that the wild-type plants were nearly always slightly ahead of their acyanogenic siblings, and there was generally a 30% reduction in grain yield. ^ A separate study suggested that seedling dhurrin content is a predictor of post-anthesis stay-green capacity. We designed a second experiment to test the stay-green capacity of the C493Y mutant and the wild-type under well-watered and drought-stressed conditions in the greenhouse. Plants of wild-type BTx623 and acyanogenic EMS 5085 (Cyp79A1-2) and EMS 932 (dhr2-1) were planted in separate hills in the same pots. CCI was measured weekly and drought stress was imposed after anthesis. In general, the mutant lines had lower CCI than the wild-type, expecially under drought conditions. We believe this study could expand our knowledge of the function of dhurrin in sorghum and potentially may lead to development of genetic materials that could be used to create forage sorghum lines that eliminate the risk of dhurrin toxicity.