Researchers have identified a group of genes that appear to help hemp plants respond to and detoxify herbicide exposure, providing what they describe as the first molecular reference for herbicide response in the crop.
The study, published September 14 in the Journal of Cannabis Research, combined greenhouse testing of eight post-emergence herbicides with RNA sequencing to examine how Cannabis sativa responds at the molecular level.
Researchers first treated hemp plants with eight herbicides representing several different mechanisms of action. Three ACCase inhibitors, pinoxaden, quizalofop-ethyl and clodinafop-propargyl, had relatively little effect on plant growth. Biomass was reduced by 23%, 25.2% and 11.9%, respectively, with results statistically comparable to untreated plants.
Other herbicides were far more damaging. Atrazine, metribuzin, metsulfuron-methyl and oxyfluorfen caused severe biomass reductions and ultimately killed the plants within 28 days. Oxyfluorfen caused particularly rapid damage, producing chlorosis and complete mortality within one week.
Bispyribac-sodium produced an intermediate response, reducing biomass by 43.5% at the tested field rate but allowing plants to survive. Even at twice that rate, researchers did not observe complete plant mortality. That partial tolerance led the team to investigate the plant’s molecular response to bispyribac-sodium in greater detail.
RNA sequencing found substantial changes in gene activity after treatment. Researchers identified 1,102 differently expressed genes after 24 hours and 595 after 48 hours. The early response included activation of signaling, secondary-metabolite production and systems involved in processing foreign chemicals, while later activity shifted more heavily toward oxidative stress responses and protein repair.
Of particular interest were 21 detoxification-related genes that were consistently activated at both time points. They included six glutathione S-transferase genes, seven glycosyltransferase genes, seven cytochrome P450 genes and an ABC transporter.
Together, those systems appear to form a multistage defense mechanism. Cytochrome P450 enzymes can help chemically modify herbicides, glutathione S-transferases and glycosyltransferases can convert them into forms that are easier for the plant to handle, and ABC transporters can help move or isolate the resulting compounds. Researchers said the findings point to a coordinated detoxification response rather than individual genes acting independently.
The results could eventually help researchers develop more effective weed-management strategies for hemp, which currently has fewer herbicide options than many conventional agricultural crops.
However, the authors cautioned that the experiments were performed under controlled greenhouse conditions. Field testing across different hemp varieties and growing environments will be needed before the findings can be translated into agricultural recommendations.
