Bensulfuron‐methyl resistance conferred by various amino acid substitutions in acetolactate synthase in <i>Ludwigia prostrata</i>

Abstract The decreased or lost control efficacy of bensulfuron‐methyl in controlling Ludwigia prostrata , a troublesome weed of most rice‐growing areas in China, has been frequently observed. Hence, 24 L. prostrata populations collected from Jiangsu Province, China, were surveyed for their resistance levels and potential resistance mechanisms. Dose–response assays confirmed that 45.8% of L. prostrata populations had evolved varying degrees of resistance to bensulfuron‐methyl, with resistance factors ranging from 6.7 to 188.3. ALS sequencing revealed that five various amino acid substitutions (P197S, P197L, P197A, P197Q and D376E) in LpALS2 mainly contributed to bensulfuron‐methyl resistance in these resistant L. prostrata populations. Additionally, 11, 3, 2, 1 and 1 populations showed cross or multiple resistance to pyrazosulfuron‐ethyl, penoxsulam, bispyribac‐sodium, imazamox and carfentrazone‐ethyl, respectively. MCPA‐Na, fluroxypyr, and bentazone, commonly used in paddy fields, remained largely effective against L . prostrata , with no plants of 24 populations surviving the field‐use rates of the three herbicides. Moreover, a molecular diagnosis for the diverse Pro197 mutation in resistant plants was created using a cleaved amplified polymorphic sequence (CAPS). This finding characterises the herbicide resistance patterns of L . prostrata and will facilitate the formulation of targeted resistant weeds management systems.