Purdue University researchers have confirmed the long-held hypothesis that sorghum deters insects from feeding on its leaves by releasing hydrogen cyanide, a University release said Wednesday.
Mitch Tuinstra, professor of plant breeding and genetics, and Brian Dilkes, assistant professor of horticulture and landscape architecture, found that insects preferred the leaves of a mutant sorghum plant with an abnormally slow release of cyanide to those of a wild-type sorghum plant with a normal cyanide-release rate.
Fall army worms fed on the leaves of the mutant sorghum even though the leaves contained similar levels of dhurrin – the chemical compound responsible for synthesizing hydrogen cyanide – as those in normal sorghum plants.
"This study separates for the first time the accumulation of dhurrin from the release of hydrogen cyanide," said Dilkes. "Both the mutant and normal sorghum plants contain dhurrin, but it's the rate of cyanide release that causes the insects to avoid one in favor of the other. It's a beautiful interaction between animal behavior and plant chemistry."
While the grain of sorghum is edible, its leaves can sometimes contain levels of hydrogen cyanide that are toxic to humans and animals. Livestock producers have long known that feeding sorghum leaves harvested at certain growth stages, and particularly under stress conditions such as drought, can result in cyanide poisoning of livestock. When properly managed, however, sorghum leaves can be safe forage for cattle.
Next-generation sequencing assists process
Identification of genes that control cyanide production and release could lead to the development of cyanide-free sorghum plants.
Tuinstra and Dilkes identified a sorghum mutant with an exceptionally slow cyanide-release rate. They located the gene responsible for the defect by using next-generation sequencing, which Tuinstra explained works like a text editor.