本研究利用種子胚根伸長及秧苗生長勢對丁基拉草之劑量反應測試，比較藥劑對秈、稉稻生育抑制之品種間差異，作為除草劑安全使用之參考。將丁基拉草配置成不同處理濃度，分別測試對水稻各品種種子之胚根及胚軸伸長之抑制反應。測試品種對丁基拉草胚根伸長之反應以台稉9 號最為敏感，台農67 號與台中秈10 號次之。台農67 號及台中秈10 號之胚根生長隨丁基拉草劑量的改變所受影響則較明顯。測試品種之胚軸伸長反應對丁基拉草之敏感程度，依序為台稉9 號、台農67 號及台中秈10 號。由胚根與胚軸伸長之50%抑制劑量(GR50)顯示，測試之18 個水稻品種，胚根伸長作用對丁基拉草之劑量反應，均較胚軸為敏感，且一致性頗高。丁基拉草處理對秧苗根長之GR50 顯示，台稉9 號、台農71 號、台南11號、台東30 號、越光等測試品種均低於10 ppm，台中秈10 號及台中秈17 號則高於200 ppm，其餘品種介於11-83 ppm 間。台東30 號、越光兩品種之株高GR50 分別為10 及11 ppm，為測試水稻中對藥劑反應較為敏感之品種。同時台東30 號之鮮重GR50 亦最為敏感(24 ppm)。比較丁基拉草對不同品種水稻之根長、株高及鮮重等生長抑制之差異，以根長反應最為敏感，次為株高，鮮重在品種間的變化較為明顯。由根長、株高及鮮重之GR50 顯示，測試之水稻品種中，以台東30 號對丁基拉草最為敏感，台中秈10 號及台中秈17 號之根長、株高及鮮重反應對藥劑的忍受性較高且趨勢頗為一致。

Butachlor is a widely used herbicide for controlling annual weeds of transplantedrice field in Taiwan. It shows inadequate use at sensitive varieties could result inphytotoxicity of rice plant. This research was conducted to evaluate phytotoxic potentialof butachlor on rice varieties and measured traits associated with seedling emergenceand vigor of rice. Bioassay used involved planting pre-germinated seeds of tested ricevarieties in filter papers soaked in herbicide solutions and measuring the radical andhypocotylar lengths after 7 days. A closer dose-response relationship existed betweenradical elongation and concentration in the range of 0-250 ppm. Differential sensitivityof tested rice varieties to butachlor was quantified by determining the herbicide ratesrequired to reduce root length, plant height and fresh weight by 50% (GR50 values).Data indicated that TT30 was generally more sensitive than other varieties. The GR50values of TCS10 and TCS17 increased about 5 to 10 times compared with those ofTT30. The present results revealed a state of stress induced in seedlings of rice varietiesby the treated dose of butachlor with differential phytotoxicity.