Varied occurrence of diverse sulfonylurea‐resistant biotypes of Schoenoplectus juncoides [Roxb.] Palla in Japan,as classified by an acetolactate synthase gene mutation

Suspected sulfonylurea (SU)‐resistant Schoenoplectus juncoides plants were collected from rice paddy fields at 24 sites in Japan in order to discover the occurrence pattern of target‐site substitutions on a nationwide scale and at a local field scale. A genetic analysis of the two acetolactate synthase (ALS) genes, ALS1 and ALS2, of the collected plants confirmed that a single‐nucleotide mutation at the Pro₁₉₇, Asp₃₇₆ or Trp₅₇₄ site of either ALS1 or ALS2 existed in each suspected SU‐resistant plant. On a nationwide scale, it was shown that the ALS1 mutations and the ALS2 mutations occurred at a similar frequency, that the P197S and the P197L substitutions were found most frequently among all the substitutions, and that the W574L substitutions (known as global resistance to any ALS‐inhibiting herbicide) were found at a relatively low frequency but in a geographically wide range. In the local field‐scale survey, which was conducted at two sites in Hyogo Prefecture, it was shown that the substitutions were less diverse, compared to on a nationwide scale, probably because the investigation involved a limited number of local fields, and that several substitutions and a susceptible biotype were found in single fields suggesting that a number of collections is required in order to understand the local SU‐resistant status of S. juncoides. In addition, this study reported new findings, that of the P197R, P197T and D376E substitutions in S. juncoides. This set of diverse substitutions in a weed species can be used for further research purposes.