Pro‐197‐Ser mutation combinations in acetolactate synthase (ALS) homoeologous genes affect ALS inhibitor herbicide resistance levels in Monochoria korsakowii

Abstract BACKGROUND Monochoria korsakowii is a common broadleaf weed found in rice ( Oryza sativa ) fields. Acetolactate synthase (ALS) inhibitor herbicides are commonly used to control broadleaf weeds in rice fields. However, prolonged herbicide use has exacerbated resistance issues. In this study, we evaluated the resistance to ALS inhibitors in populations where the same mutation occurred separately and simultaneously in the two ALS homoeologous genes ( ALS 1 and ALS 2) and investigated the resistance mechanisms in M. korsakowii . RESULTS Monochoria korsakowii exhibited high resistance to bensulfuron‐methyl, low resistance to penoxsulam, and sensitivity to imazethapyr. Three resistant populations were identified: M‐1 and M‐2, which independently evolved the Pro‐197‐Ser mutation in ALS 1 and ALS 2, respectively, and M‐3, which harbored this mutation in both ALS 1 and ALS 2. The sensitivity of ALS isolated from these populations to herbicide inhibition corresponded to the whole‐plant resistance levels. Subsequently, we cloned and transformed Pro‐197‐Ser‐mutated ALS 1 and ALS 2 into Arabidopsis thaliana . The resistance of homozygous A. thaliana to bensulfuron‐methyl and penoxsulam aligned with bioassay trends. Furthermore, we measured the ploidy, relative expression, and copy number of ALS 1 and ALS 2, and found no significant differences, suggesting that the evolution of resistance was primarily attributed to the Pro‐197‐Ser mutation. Finally, we developed a derived cleaved amplified polymorphic sequence marker for detecting Pro‐197‐Ser mutation in ALS . CONCLUSION The same mutation occurring separately in homoeologous genes resulted in similar resistance levels, whereas simultaneous mutations in homoeologous genes led to increased resistance levels. © 2024 Society of Chemical Industry.