Controlling levels and tolerance mechanisms of red rice accessions to protox inhibitor herbicide, oxyfluorfen

Red rice (Oryza sativa L.) is one of the most troublesome weeds in most rice growing regions of the world. Thus, this study was conducted to determine the tolerance levels of various red rice accessions to the protox inhibitor, oxyfluorfen and also examined tolerance mechanisms in selected red rice accessions. Tolerance levels obtained from seed bioassay were lower than those obtained from whole-plant bioassay. Twenty-one of 38 red rice accessions in seed bioassay and 37 of 38 accessions in whole-plant bioassay were tolerant to oxyfluorfen. The most tolerant accession, R 2, was >20 times more tolerant in wholeplant bioassay and 13 times more tolerant in seed bioassay than the susceptible accession, R 116. This was supported by the results of experiments on levels of superoxide, H₂O₂ and MDA productions. In addition, the accumulations of proto IX in R 116 were more increased than in R 2 after oxyfluorfen treatment. The tolerance mechanism in R 2 was not related to higher antioxidant enzyme activities. However, higher ascorbate contents may contribute to greater tolerance of R 2 to oxyfluorfen.