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Resistance mechanism of rice seedlings to bentazon herbicide among rice lines
Bentazon is usually used in weed control for rice and peanut crops. If the growth of rice, cv. TNG67, seedlings was affected and how the physiological response was influenced by bentazon, especially for the resistant- and the susceptible-lines among Japonica- and Indica-type rice, were investigated. According to the dose-response to bentazon of five growth characters including plant height, shoot fresh weight, total chlorophyll, chlorophyll a and chlorophyll b of TNG67 seedlings at the V3 stage, the effective concentration of leaf-applied bentazon causing 50% reduction of response (EC50) was determined. And further study on the physiological resistant mechanism existed in bentazon-resistant and -susceptible lines of rice under this concentration of bentazon was conducted. As a result of screening the bentazon-resistant and —susceptible lines of rice, lines M202 and FSK are referred to resistant- and susceptible-line, respectively, among Japonica-type rice, as well as the TCSW1 and IR36 are referred to resistant- and susceptible-line among Indica-type, respectively. The bentazon-resistant line, M202, and TNG67 were suffered from little or a slight visible injury, photosynthesis inhibition and accumulation of MDA after bentazon application compared to other lines. Further analysis of the physiological mechanism of resistance for the bentazon-resistant and -susceptible lines among Japonica- and Indica-type rice was conducted. Experimental results indicate that the resistant line of Japonica-type, M202 and TNG67, absorbed more 14C-bentazon, but most of 14C-isotopes absorbed either accumulated in bentazon-treated leaf or translocated out of the treated leaf to older leaves subsequently. It is also found that the phytotoxicity resulted from residual bentazon and its metabolite was slight in these two rice lines. The hydroxybentazon (bentazon-6-OH) could be detected in the bentazon-resistant rice lines, M202, but not in other rice lines, indicating that M202 and TNG67, especially for the former line had stronger ability to metabolite more bentazon. For the bentazon-susceptible lines, FSK and IR36, which absorbed less 14C-bentazon during treatment but most of the 14C-isotopes absorbed translocated out of treated leaf and accumulated in young leaves subsequently. More accumulation of bentazon at the younger leaf might result in death of rice seedlings. In addition, more residual bentazon and stronger phytotoxicity were also confirmed in these two bentazon-susceptible lines. And less polar metabolite was obtained. This result indicates that the bentazon-sensitivity of FSK and IR36 were due mainly to the lower ability of bentazon metabolism. Reviewing the experimental results of this study, it suggested that the bentazon-resistant mechanism existed in resistant lines, M202 and TNG67, is primarily result from the stronger metabolism of bentazon, especially the generation of bentazon-6-OH for the line M202. Besides, that the most of absorbed bentazon translocated to older leaves and/or deposited at the site of bentazon application also involved in the resistance mechanism.
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