S&W Seed Company launches new prussic acid free sorghum 

It’s well-known that livestock shouldn’t graze some forages after a freeze or during drought conditions due to prussic acid build up in the plant.  

A seed company and a university have been working to help alleviate that problem with a new prussic acid free sorghum.  

S&W Seed recently launched a new PF hybrid, according to Scott Staggenborg, S&W Sorghum product marketing director, and Mitch Tuinstra, professor of plant breeding and genetics at Purdue University. The pair recently discussed the development of the trait and how it will help those grazing plants that produce dhurrin. 

Development

According to S&W, dhurrin is a compound produced primarily by sorghum, but is found many other plant species. Under the right conditions it can be converted to hydrogen cyanide or HCN gas—commonly known as prussic acid. When dhurrin is converted to prussic acid when plants are damaged, frozen or under drought stress it can kill ruminant livestock. 

“Prussic acid has been a real challenge in sorghum for a lot of years,” Staggenborg said.  

Tuinstra had a conversation about the possibility of the PF hybrid awhile back and he was persistent. 

“I slowly developed a list of things that I thought were important in terms of technology development for this crop, which really has unusually well adapted qualities for dry land production,” Tuinstra said. 

The dhurrin production was one of the traits that caught Tuinstra’s attention early, because it’s a unique metabolite of sorghum. There’s several plant species able to produce metabolites or cyanogenic glucosides.  

“These are sugars that have various kinds of complexities,” he said. “They’re involved in controlling herbivores.” 

When thinking about how these traits control animal or insect feeding, Tuinstra said many people thought it was key to the drought tolerance of sorghum. 

“And what’s remarkable is the fact that we have a crop that’s designed as a forage crop, and yet it still needs to be managed for the secondary metabolite that can cause death to animals by cyanosis,” he said. 

Prussic acid is cyanide and when it accumulates in plant material it becomes deadly. Tuinstra kept digging deeper.   

“Sorghum is actually the model species for studying cyanogenic leukocyte metabolism. And I thought, boy, if we could just figure out a way to block that first enzyme, we could completely shut down this pathway, and there’d be no dhurrin production and no HCN production,” he said. 

Tuinstra and his team started looking at naturally occurring sorghum varieties from all over the world for variants that would help “make” the sorghum they were looking for. But they weren’t able to find them. This led to his mutagenesis project. 

“We took sorghum seeds, treated them with a chemical that causes DNA damage, and when you damage the DNA, sometimes you damage the genes that are encoded,” he said. 

At Purdue, Tuinstra had about 10 graduate students working on the project and over the course of about 20 months, his team looked at 50,000 plants. They found there were occasionally plants that were not able to synthesize the metabolite. Since they couldn’t make dhurrin, they were unable to make prussic acid either. 

“After a little bit of careful manipulation and studying of the genes and we discovered that in the first enzyme in the pathway there was a mutation in the gene and it completely killed the gene,” he said. “The gene is no longer able to produce an enzyme that functioned, consequently, no dhurrin biosynthesis.” 

Staggenborg said by 2019, Tuinstra had come back to him with finished hybrids and had been through several iterations on the parent development line. Due to the development in Indiana, S&W had problems with replicating it in west Texas. 

“So seed production became a bit of a challenge,” he said. “It took a couple iterations to get to where we are today, with a commercial product ready to launch.” 

Specifics

The PF hybrid from S&W is non-GMO because of the way it was developed, Staggenborg said.  

“It was just good old-fashioned labor,” he said. “There was a lot of lot of leaf punches collected over a long period of time by a bunch of undergrad workers.” 

Right now there’s one PF product on the market, and that’s important, according to Staggenborg. Many producers who rely on sorghum to graze are challenged by prussic acid and struggle to find the right kind of solution. 

“We get a frost or a drought, being able to graze the sorghum Sudan grass that you have out in your field becomes a real problematic situation,” Staggenborg said. “You can take some tests, and there’s a good chance that the material you have out in the field is high in prussic acid. You can’t graze it. So, there’s this piece of mind component of what do I do?” 

Producers have animals to manage, and he believes having a PF forage can help save time and labor. Especially during the fall when labor is at a premium due to harvest and other farm activities. 

“But nonetheless, if you’ve got cattle grazing a sorghum Sudan grass in the fall, and you’re trying to do all of these other things, and there’s a frost that night, you have to get up very early in the morning or maybe in the middle of the night to move animals,” he said. “So that takes time, probably takes a good half a day to get them all moved, and now you have to care for them afterwards.” 

It can also help extend the grazing period when labor is limited and that can be helpful for some producers. 

“With prussic acid free, you have the peace of mind that the prussic acid is not going to appear in the growing plant in the fields you have it planted in,” Staggenborg said.  

Staggenborg surveyed a couple of PF growers in January, asking how many days they thought they were able to keep grazing after the first freeze.  

“The biggest group thought maybe it was two weeks to a month,” he said. “You can look at what a day of grazing is worth to you and add some economics to this. This fall grazing, extended grazing period may be something that many of us have not thought about is one of the benefits to this technology.” 

The hybrid is available commercially with S&W having exclusive rights to the PF trait. It is expected to be available soon in similar genetics as Sordan 79 and SP4105 BMR. Look for the PF at the end of a hybrid name to know if it is prussic acid free. S&W and Purdue have been conducting ongoing research to ensure hybrids perform equal or better than current non-PF hybrids. Third party university trials combined with on farm grazing trials have produced favorable yields without compromising nutrition.  

For more information about the PF hybrid visit swseedco.com. 

Kylene Scott can be reached at 620-227-1804 or [email protected].