FAYETTEVILLE — Grain sorghum is widely grown in arid environments as an animal feed grain, but weedy grass control in the crop is a big challenge due to limited post-emergent herbicide options.
A joint effort between the Arkansas Agricultural Experiment Station and Texas A&M AgriLife Research has resulted in development of a trait that was patented and bred into conventional grain sorghum with resistance to herbicides targeting johnsongrass and other troublesome grass weed species. The experiment station is the University of Arkansas System Division of Agriculture’s research arm.
The breeding work began in 2019 with the discovery of johnsongrass on an Arkansas roadside that showed resistance to acetyl-CoA carboxylase-inhibiting herbicide, also known as ACC-ase. ACC-ase affects plant growth by affecting fatty acid synthesis, a key step in membrane formation. The ACC-ase gene in the johnsongrass was bred into a grain sorghum, currently known as ArkTam™.
Jason Norsworthy, Distinguished Professor of weed science with the Arkansas Agricultural Experiment Station, said a grain sorghum that is resistant to ACC-ase herbicides is beneficial because there are fewer ACC-ase chemistries that work on grass weed species than the other major herbicide for the job — Acetolactate synthase, or ALS, herbicides — which target the acetolactate synthase gene in plants to inhibit growth by affecting synthesis of certain amino acids.
Norsworthy, who also holds the Elms Farming Chair of Weed Science, shares inventorship on the patent for the trait used in ArkTam™ with Bill Rooney, Muthukumar Bagavathiannan and George Hodnett at Texas A&M AgriLife Research.
Rooney is the Texas A&M AgriLife Research sorghum breeder, professor and Borlaug-Monsanto Chair for Plant Breeding and International Crop Improvement.
Bagavathiannan is a Texas A&M AgriLife Research weed science and cropping systems agronomist and the Billie Turner Professor of Agronomy.
Hodnett is a senior research associate in the department of soil and crop sciences for Texas A&M AgriLife Research.
“All the work so far looks very promising,” said Parker Cole, associate director of Technology Commercialization for the University of Arkansas System Division of Agriculture. “We are excited about the opportunity to help grain sorghum farmers, including those in Arkansas, by working with Texas A&M in developing this new trait.”
Why ACC-ase?
Only a limited number of herbicides are available to provide post-emergence control of selective grass weeds in grain sorghum crops. And the herbicides currently labeled for use with grain sorghum have strict use restrictions, low efficacy on johnsongrass, or weed resistance issues, Norsworthy said.
“From an herbicide-resistance standpoint, there are more weeds resistant to ALS herbicides worldwide than any other herbicide that we have out there,” Norsworthy added. “And weeds rapidly evolve resistance to that type of herbicide.”
Reasons for that wider resistance to ALS chemistry is due in part to them being used on both grasses and broadleaf weeds like Palmer pigweed, whereas the ACC-ase chemistry is strictly used on grasses, Norsworthy said.
Experiment results
An experiment was conducted at the Milo J. Shult Agricultural Research and Extension Center in Fayetteville to determine the effectiveness of two ALS-inhibiting herbicides and nine ACC-ase herbicides on ArkTam™ sorghum and problematic grass weed species.