Resistance profile study of SU-resistant Sagittaria trifolia in a comparison of seedlings and tuber-derived plants

Abstract

Sagittaria trifolia, a perennial weed of Alismataceae in Japanese rice paddies, has a single ALS gene, and both target and non-target-site resistance are known in the SU resistance of this species. In this study, the target-site resistance profile at the whole-plant and enzyme levels was investigated using self-pollinated S1 seedlings from a parent plant heterozygous for a Pro197Ser ALS mutation and their clonal tubers. Our objectives were to reveal differences and similarities between whole-plant resistance of seedlings to imazosulfuron and that of tuber-derived plants and to correlate the whole-plant responses to enzymatic inhibition, as well as to quantify the effects of mutant ALS allele stacking. Genotyping confirmed a Mendelian segregation ratio (1:2:1) among S1 plants for wild-type, heterozygous, and homozygous ALS mutations. Enzymatic assays showed that resistance correlated with the number of mutant alleles, and heterozygous plants exhibited a double-sigmoid curve plateauing at 50%, indicating the function of a 50:50 wild-type to mutant enzyme ratio. Studies of tuber-derived plants showed that resistance increased with more mutant alleles, but with a disproportionate jump over 3000-fold from wild-type to heterozygous, and only 5-fold from heterozygous to homozygous, indicating a saturating tendency in the stacking effect of mutations. The dose response of S1 seedlings was consistent with Mendelian segregation of genotypes and suggested a similar saturation of resistance increase due to allele stacking as observed in tubers, with comparable dose–response patterns across identical genotypes.