Search

BACKGROUND: Japanese brome (Bromus japonicus Thumb.) is one of the problematic annual weeds in winter wheat (Triticum aestivum L.) and is generally controlled by acetolactate synthase (ALS) inhibitors. Repeated use of the ALS inhibitor propoxycarbazone‐Na resulted in the evolution of resistance to this herbicide in three B. japonicus populations, i.e., R1, R2, and R3 in Kansas (KS). However, the level of resistance and mechanism conferring resistance in these populations is unknown. The objectives of this research were to (i) evaluate the level of resistance to propoxycarbazone‐Na in R1, R2, and R3 in comparison with a known susceptible population (S1), (ii) investigate the mechanism of resistance involved in conferring ALS‐inhibitor resistance, and (iii) investigate the cross‐resistance to other ALS inhibitors. RESULTS: Dose–response (0 to 16x; x = 44 g ai ha−1 of propoxycarbazone‐Na) assay indicated 167, 125, and 667‐fold resistance in R1, R2 and R3 populations, respectively, compared to S1 population. ALS gene sequencing confirmed the mutations resulting in amino acid substitutions, i.e., Pro‐197‐Thr (R3, R1)/Ser (R2, R1) bestowing resistance to these ALS inhibitors. Such amino acid substitutions also showed differential cross‐resistance to sulfosulfuron, mesosulfuron‐methyl, pyroxsulam, and imazamox among resistant populations. Pretreatment with malathion (a cytochrome P450 enzyme‐inhibitor) followed by imazamox treatment suggested cross‐resistance to this herbicide possibly via metabolism only in R3 population. CONCLUSION: Overall, these results confirm the first case of target‐site based resistance to ALS inhibitors in B. japonicus in the US, highlighting the need for exploring herbicides with alternative modes of action to enhance weed control in winter wheat. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Grain sorghum is a versatile crop, which can thrive under limited water and other inputs. However, crop loss from weed infestation continues to be a major constraint in grain sorghum production. Particularly, post‐emergence grass weed control is a great challenge in grain sorghum due to the lack of herbicide options. Unlike in other major crops, such as maize or soybean, herbicide‐resistant sorghum technology that can facilitate weed control throughout crop growing season is not available to growers yet. The development of herbicide‐resistant sorghum can have potential to improve weed management, including post‐emergence grass weed control. One of the major concerns in the development of such technology in sorghum is escape of resistance traits into weedy relatives of sorghum (e.g. shattercane and johnsongrass). This review focuses on sources of herbicide resistance in sorghum, the status of the development of herbicide‐resistant sorghum technologies, overview of breeding methods, and limitations in the development of such sorghum technology as well as economic benefits for sorghum growers. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]