Determination of genotoxic effects of Quizalofop-P-etyl herbicide in onion roots (Allium cepa L.) by RAPD and comet assays

This research was performed to determine the genotoxicity potential of quizalofop-P-ethyl (QPE) herbicide at different concentrations and exposure times in Allium cepa L. (common onion). The rooted onion bulbs (in distilled water for 24 h) were treated with negative control (distilled water), positive control (10 ppm methyl methanesulfonate, MMS) and different concentrations (0.75, 1.5 and 3.0 ppm) of QPE for 48 and 96 h. The effects of QPE herbicide on the root growth, total soluble protein content of root tips, the level of single stranded DNA breaks revealed by comet assay and changes in genomic template stability shown by random amplified polymorphic DNA (RAPD) assay were analyzed at the end of these periods. At both treatment periods, the root growth was significantly inhibited at high concentrations (1.5 and 3.0 ppm) of QPE (P < 0.5). Total soluble protein content of root tips in the negative control was significantly reduced in 96 h treatment in comparison to 48 h treatment (P < 0.5). In comparison to their negative controls, all QPE concentrations at 48 h decreased the total soluble protein content of root tips, while once at 96 h increased it significantly (P < 0.5). Among the all QPE concentrations, the highest (13 %) decrease in protein content was measured in the root tips exposed to 1.5 ppm QPE at 48 h, whereas the highest increase (10 %) was determined for the root tips treated with 3.0 ppm QPE at 96 h. In comparison to 48 and 96 h comet results, measured 14.25±2.89 and 16,25±1.43 AU, respectively, induction of single stranded DNA breaks (32.5±2.9-42.5±4.9 AU) were determined in the nuclei of root tips exposed different concentrations of QPE. However, there was no significant difference among the application periods and concentrations of QPE (P < 0.5). The highest single stranded DNA breaks were determined for 48 (70.25±3.7 AU) and 96 h (89.25±3.9 AU) positive control treatments. 94 RAPD bands in the range of 319-2219 bp were amplified in the negative control by using 9 oligo-primers. In RAPD analysis, band lost and/or gain in RAPD profiles were determined in all treatment groups in comparison to RAPD profiles of negative control. In comparison to negative control, the number of RAPD band changes (band lost and band gain) at 48 h QPE treatments were higher than once at 96 h treatments. The UPGMA dendogram developed from RAPD results clustered all treatments in to four groups: (i) positive control (48 and 96 h), (ii) 48 h QPE treatments (0.75, 1.5 and 3.0 ppm), (iii) negative control (iv) 96 h QPE treatments (0.75, 1.5 and 3.0 ppm). According to the RAPD results, positive control treatments caused to the highest change in the number of RAPD profiles among the treatment groups. In comparison to their negative controls fixed to 100 %, a decrease in root length and genomic template stability values and an increase in the level of single stranded DNA break was determined in onions treated with QPE for 48 and 96 h. However, the level of decrease or increase in these parameters were determined high at 48 h treatments in comparison to 96 h ones. Our research findings clearly indicated that quizalofop-P-ethyl has genotoxic effects in Allium cepa L.