Abstract
Benzobicyclon has shown varying results in controlling weedy rice, including those with imidazolinone (IMI) resistance. Tolerance to benzobicyclon in cultivated japonica rice, but not indica or aus-like cultivars, is conferred by a fully functional HPPD Inhibitor Sensitive 1 (HIS1) gene. Herein, a diagnostic Kompetitive Allele Specific PCR (KASP) assay was developed to predict the HIS1 genotype of weedy rice plants from 37 accessions and correlated to their response to benzobicyclon in the field. Two-thirds of the 693 weedy rice plants screened were tolerant to benzobicyclon (371 g ai ha(-1), SC formulation) at 30 days after treatment (DAT). Thirty-four percent of plants were homozygous for the HIS1 allele and 98% of these plants exhibited field tolerance. However, the his1 genotype did not always correlate with field data. Only 52% of his1 plants were considered sensitive, indicating that the single nucleotide polymorphisms (SNPs) chosen in the KASP assay are not a reliable tool in predicting his1 homozygous plants. In an additional experiment, 86% of the 344 plants with at least one copy of the ALS(S653N) trait harbored a HIS1 allele, suggesting fields infested with IMI herbicide-resistant weedy rice are unlikely to be controlled with benzobicyclon.