Role of metabolization and conjugation of herbicides in tolerance of white oats to 4-Hydroxyphenylpyruvate Dioxygenase (HPPD) enzyme inhibitors

Abstract

The success of chemical control is dependent on crop tolerance to herbicides and their efficiency in controlling weeds. Thus, knowledge of the tolerance level of cultivated plants and the tolerance mechanism involved is crucial for safe herbicide use. The objective of this study was to evaluate the effect of metabolization (malathion) and conjugation (NBD-Cl) inhibitors on the tolerance of white oats to the herbicides mesotrione and tembotrione. The experiment was carried out under field conditions in the 2021 crop, in an RBD, with nine treatments, namely: T0- control (no application); T1- malathion; T2- NBD-Cl; T3- mesotrione; T4- mesotrione+malathion; T5- mesotrione+NBD-Cl; T6- tembotrione; T7- tembotrione+malathion and T8- tembotrione+NBD-Cl. The plant characteristics were evaluated for plant intoxication, SPAD index, levels of chlorophyll a, b and total carotenoids, yield components, yield and industrial grain quality. Symptoms of intoxication in oat plants started at 7 DAA and increased up to 14 DAA in treatments containing mesotrione or tembotrione. Plant recovery started at 21 DAA, and it was intensified at 28 DAA. Intoxication levels were not affected by the addition of the metabolization inhibitors malathion (43.1%) and NBD-Cl (36.2%). There was no change in other variables tested under the control treatment. Based on these findings, it can be concluded that there was no change in the level of tolerance of white oats to the herbicides mesotrione or tembotrione after application of malathion and NBD-Cl. This outcome suggests that metabolization or conjugation is not the main mechanisms that make white oat tolerant to HPPD enzyme inhibitors.