Differential Growth Response of Acetolactate Synthase Inhibitors-resistant Sagittaria trifolia Originated from Seeds and Tubers

Abstract

Continuous use of acetolactate synthase (ALS) inhibitors has led to the selection of herbicideresistant Sagittaria trifolia in paddy fields. Herbicide-resistant (R) S. trifolia was first reported in 2011 in Korea. The objective of this study was to investigate the level and mechanism of resistance and understand the fitness of R biotypes using R and susceptible (S) S. trifolia biotypes originated from seeds and tubers. Whole plant dose-response showed that the R biotypes originated from tubers were highly resistant to cyclosulfamuron and moderately resistant to penoxsulam and imazaquin, with R/S ratios of 250, 13 and 8, respectively. Compared to the S biotype, the R biotype originated from tuber had an amino acid substitution at the position of a Pro197-Leu residue of als gene, a well-known mutation site that could confer resistance to sulfonylurea, triazolopyrimidine, and imidazolinone herbicides. Additionally, the germination rate and growth of the S biotypes originated from seeds were lower than those of the R biotypes. The growth of the S biotypes originated from tubers was more vigorous than that of the R biotypes. Once the seed of R biotypes move to uninfected paddy fields, the germination rate of R biotypes is probably more than that of existing S biotypes. If ALS inhibitors are applied into paddy fields, R biotypes can survive and even produce tubers that can continually propagate and probably become dominant in the population in uninfected paddy fields. Thus, increasing the application rate of ALS inhibitors to kill R biotypes probably can enhance ALS-inhibitors’ selection-pressure.