| In recent years, with the promotion of water-seeded rice, weedy rice (Oryza sativa f. spontanea) has become a serious weed rapidly. In some areas, it has become the third weed and caused huge losses. Pretilachlor is one of the best herbicides to control grass weeds. However, weedy rice and cultivated rice have similar genetic type, so pretilachlor is limited to apply to control weedy rice. Therefore, it has become an urgent problem to broaden the scope of pretilachlor. In order to find effective and safe ways to control weedy rice without damaging to cultivated rice, this paper was conducted to study the effect of pretilachlor on the weedy rice and cultivated rice by laboratory biossay and analyzed the fenclorim reduced the phytotoxicity of pretilachlor on cultivated rice by laboratory biossay and field trail. It was hoped to become an effective technology to serve agricultural production. In addition, this paper analyzed the mechanism of fenclorim protecting cultivated rice from phytotoxicity of pretilachlor by physiological and biochemical tests. Detailed results are as follows.1. Phytotoxicity of pretilachlor on weedy riceIn order to find effective ways to control weedy rice by using herbicide pretilachlor, this paper studied the effect of pretilachlor on weedy rice at different time and different dose of pretilachlor by laboratory biossay. The result showed that 225～900g ai./hm2 pretilachlor caused 70.89%～97.47% and 76.74%-99.46% inhibition of emergence and fresh weight at pre-emergence date.225-900g a.i./hm2 pretilachlor caused 56.06%～89.39% and 47.22%～91.53% inhibition of emergence and fresh weight at emergence date.225～900g a.i./hm2 pretilachlor caused 33.33%～ 77.27% and 33.15%～70.42% inhibition of emergence and fresh weight at 1.5 leaf stage. Therefore, it was best to use pretilachlor for control weedy rice at pre-emergence date. And 450g a.i./hm2 pretilachlor could cause above 90%inhibition of emergence and fresh weight at pre-emergence date. Apart from this, pretilachlor was not safe to cultivated rice. The growth of weedy rice was inhibited significantly but also the rice by the herbicide pretilachlor. And cultivated rice was more sensitive than weedy rice to pretilachlor. The ED50 of Xin-6、Nan-45 and weedy rice was 131.25、216.35 and 243.75g a.i./hm2.2. Studies on the technology of fenclorim reducing the phytotoxicity of pretilachlor on cultivated riceIn order to find effective technology to control weedy rice without damaging to cultivated rice, this paper revealed the effect of fenclorim for reducing the phytotoxicity of pretilachlor to cultivated rice by laboratory biossay and analyzed fenclorim protected cultivated rice from the phytotoxicity of pretilachlor on field trail. The results indicated that fenclorim was safe to cultivated rice without damaging to emergence and growth of cultivated rice. Nan-45 and Xin-6 soaked in 10mg/L and 30mg/L fenclorim were safe when the dose of pretilachlor was 450g a.i./hm2.In addition, when the time of soaking was 6-48h, fenclorim had more capability to protect cultivated rice with more soaking time. Field trail revealed that when the soaking time of Nan-45 and Xin-6 was 48h in 10mg/L and 30mg/L fenclorim, 450-675g a.i./hm2 pretilachlor was safe to cultivated rice. But when the dose of pretilachlor was 900g a.i./hm2, the yield of rice decreased obviously.3. Studies on the mechanism of fenclorim reducing the phytotoxicity of pretilachlor on cultivated riceIn order to reveal the mechanism of fenclorim reducing the phytotoxicity of pretilachlor to rice. Physiological and biochemical tests were conducted to reveal the protective mechanism of fenclorim for cultivated rice, based on the effecting on GST activity, a-amylase for seed germination, and the contents of chlorophyllin and protein. The results of the study showed that fenclorim increased the metabolic rate of pretilachlor by increasing GST activity of cultivated rice and mitigated the phytotoxicity to cultivated rice. When the dose of pretilachlor was 56.25.112.5,225g a.i./hm2, GST activity of cultivated rice Xin-6 by soaking with 30mg/L fenclorim, compared with contrast, increased from 121.8%,98.9%.71.4%to 175.7%.141.6%.128.3%, and α-amylase activity increased from 94.3%.81.7%、63.8% to 97.7%.93.4%.89.3% with fenclorim, respectively. GST activity of cultivated rice Nan-45 by soaking with 30mg/L fenclorim, compared with contrast, increased from 119.8%.126.5%.72.2% to 144.3%.132.0%.121.5%, and a-amylase activity increased from 78.9%.72.5%.59.1% to 86.7%.85.6%.80.7% with fenclorim, respectively. Apart from this, fenclorim had capability to partly remission the inhibition of pretilachlor to cultivated rice. In other words, fenclorim could improve the tolerance of cultivated rice under the stress of pretilachlor by increasing the contents of chlorophyllin and protein. So, the mechanism of fenclorim reducing the phytotoxicity of pretilachlor to cultivated rice was the result of interaction of multiple factors. |
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