Assessment of the xenobiotic effects of 2,4-dichlorophenoxyacetic acid + 2-methyl-4-chlorophenoxyacetic acid and bromoxynil + 2-methyl-4-chlorophenoxyacetic acid herbicides in wheat

Herbicides are xenobiotic compounds. To investigate the xenobiotic effects of foliar herbicide consumption and plant response over time, two commercial selective herbicides (bromoxynil + 2,4-D (H₁), 2,4-D + 2-MCPA (H₂), and the control (zero, H₀)) were applied to seven Iranian wheat genotypes at 50% tillering. The biochemical traits were measured at six-time intervals (0–30th days after treatment). Morphological traits were measured on the 30th day after treatment. The results showed that the applied treatments significantly affected all the measured traits (P < 0.001). Therefore, these traits can be considered screening responses to xenobiotic stress caused by herbicides. For the first time, qualitative Bendict’s reagent quantification and estimation of the proximate content of sucrose as well as the 3,5-dinitrosalicylic acid reagent showed significant variation among genotypes. The change in the treated sample compared to H₀ showed that the effects of stress started at least 30 min after treatment. Consequently, the tolerant plants recovered on the 30th day after treatment. Clustering of the 20 measured traits showed that height, specific leaf weight, and chlorophyll a content could be selected as indicator traits for genotype screening. The genotypes were classified into three groups (sensitive, semi-sensitive, and tolerant) based on indicator traits. The maximum H₂O₂ concentration (a biochemical indicator of the occurrence of stress) was 980.5 µg at 30 min after treatment with H₂ and 735.1 µg on 1th day after treatment with H₁. Finally, the genotypes showed greater sensitivity to the combination herbicide from two biochemical groups of the same type (H₂) than did those from different groups (H₁).