Resistance patterns and mechanisms towards imidazolinone herbicides in Malaysian weedy rice
2023
Jamil, M.A.H. | Hamdani, M.S.A.
Rice is an essential grain for many people around the globe and is the second most consumed carbohydrate source. Weedy rice (Oryza sativa f. spontanea) is a weed that impeders rice cultivation. Due to the identical morphology of those two, it is hard to control; hence, the Clarified Planting System (CPS) was developed to effectively manage weedy rice using herbicide-resistant rice varieties. Such varieties include rice resistant to imidazolinone herbicides (IMI-rice). Nonetheless, examples of weedy resistance have been observed after several generations of planting due to improper herbicide management. This study examines the patterns and potential mechanisms of resistance to imidazolinone herbicides (IMI-herbicide). Weedy rice samples obtained from rice fields in Kelantan were subjected to screening, bioassay, and dose response experiments to determine their resistance to three chosen IMI-herbicides, and exhibited substantial resistance to them. In both seed bioassay and dose-response studies, imazapic and imazapyr exhibited high resistance. In contrast, the imazethapyr exhibited moderate level of resistance. Further molecular analyses of the AHAS gene sequence have shown that a single target-site mutation (Ser-653) has been identified for IMI-herbicide resistance in weedy rice populations and MR220CL2 rice variety. In vitro AHAS inhibition assay has further confirmed the herbicide resistance in the population of weedy rice and MR220CL2 towards the imidazolinone herbicides at the enzyme level. In conclusion, the basis of resistance of Malaysian weedy rice was confirmed to be the Ser-653-Asn mutation for all the resistant weedy rice population and MR220CL2. These findings should be able to supplement and help further studies in herbicide resistance and food security especially for rice cultivation.
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