Resistance of Sagittaria montevidensis Cham. & Schltdl. populations to acetolactate synthase inhibitors and bentazon herbicides

Background:  Sagittaria montevidensis is one of the main weeds in paddy rice, especially in the water-seeded system. The incorrect use of herbicides allowed the selection of populations resistant to the main herbicides labeled for rice.

Objective:  The objective of the experiment was to evaluate the mechanisms involved in resistance to ALS- and PSII-inhibiting (i.ALS and i.PSII) herbicides in SAGMO 32 and SAGMO 10.

Methods:  The accessions SAGMO 35 (susceptible), SAGMO 32 (resistant i.ALS and PSII), and SAGMO 10 (resistant i.ALS) were used in the greenhouse experiments. The first study evaluated the effect of CYP450 inhibitors on the activity of the herbicides penoxsulam, bispyribac-sodium, and bentazon. The second study was an in vitro analysis of ALS enzyme activity with imazethapyr and metsulfuron-methyl herbicides. The third study was sequencing the ALS and psbA genes to detect resistance-conferring mutations.

Results:  CYP450 inhibitors did not alter the efficiency of any of the herbicides tested. SAGMO 32 and SAGMO 10 showed RF (enzyme inhibition) of >600 and >13 for metsulfuron-methyl and imazethapyr. The ALS mutation Trp574Leu was detected in SAGMO, which confers resistance to imazethapyr and metsulfuron-methyl. The psbA sequence did not reveal any resistance-conferring mutations.

Conclusions:  The resistance mechanism of Sagittaria montevidensis (SAGMO 32 and SAGMO 10) to the ALS-inhibiting herbicides is due to target-site mutation, Trp574Leu. The mechanism of resistance to the herbicide bentazon remains unidentified.

Keywords:
Sagitaria; Giant arrowhead; psbA; PSII