The Potential And Security Of Imazamox To Control Weedy Rice In The Imazamox-tolerant Paddy Field

With the transfer of rural labor force,time-saving and efficient method of direct-seeded rice(DSR)has been favored by farmers for the past few years.As the area of DSR has become larger and larger,the traditional intensive farming mode has been replaced by shallow tillage and no-tillage,leading to more and more serious weed hazards in paddy fields.weedy rice,which disappeared under the intensive farming,is making a comeback.weedy rice,is a kind of annual weeds of grasses,rice family and rice genera.At present,there is no herbicide that can effectively control weedy rice,and at the same time,it is safe to rice.At present,the control of weedy rice mainly depends on farmers to pull out artificially in seedling stage and tillering stage.But that increases the cost of growing rice.Recently,some farmers have privately adopted the strategy of combining imazamox with imazamox-tolerant rice for weedy rice control.However,imazamox is a herbicide used in soybean fields and has not been registered in paddy fields,no feasibility evaluation of this strategy has been carried out,the technology has not been systematically integrated,and there is a lack of scientific guidance for the application of the drug to farmers.Therefore,the aim of this study was to evaluate the feasibility of combining imazamox with imazamox-tolerant rice for weedy rice control from the technical level.Adopts the whole plant bioassay method,determination of the resistance of the weedy rice,common paddy weeds and herbicide-resistant weeds the sensitivity of the imazamox,choose fresh weight inhibition rate and selectivity index(SI)to evaluate the imazamox for the safety of JD 372,Jin Jing 818,measured the imazamox soil residual toxicity of the afterreap crop(barley,wheat,rapeseed,brassica chinensis),screening the detoxifying effects of safe agents Bihu and Yuehu on JD 372 that is poisoned by imazamox,exploring the reason for difference sensitivity between JD 372 and weedy rice from the target enzyme ALS.The results are as follows:The sensitivity of 14 weeds to imazamox was determined by whole plant bioassay method,including Oryza sativa f.spontanea,Echinochloa crus-galli,Leptochloa chinensis,Digitaria sanguinalis(L.)Scop.,Murdannia triquetra(Wall.ex C.B.Clarke)Bruckn.af,Ludwigia prostrata Roxb.,penoxsulam-resistant Echinochloa crus-galli and cyhalofop-butyl-resistant Leptochloa chinensis.The results showed that: under 25 g a.i./ha imazamox,the fresh weight inhibition rate of three kinds of Oryza sativa f.spontanea was near 80%,the fresh weight inhibition rate of Echinochloa crus-galli,Ludwigia prostrata Roxb.,Murdannia triquetra(Wall.ex C.B.Clarke)Bruckn.,quinclorac-resistant Echinochloa crusgalli var.zelayensis,penoxsulam-resistant Echinochloa crus-galli,mefenacet-resistant Echinochloa crus-galli were all over 80%.under 50 g a.i./ha imazamox,the fresh weight inhibition rate of the above weeds,Leptochloa chinensis,Digitaria sanguinalis(L.)Scop.,Ammannia baccifera L.and cyhalofop-butyl-resistant Leptochloa chinensis were near or over 90%,but the fresh weight of Cyperus difformis L.was only55.88%.The results revealed that imazamox showed a high inhibitory effect on Oryza sativa f.spontanea,common paddy gramineae weeds and broadleaf weeds weeds,while the control effect on heterotypic sedge was not good.whole plant bioassay method was used to determine the safety of imazamox to Jindao372 and Jinjing818 at different leaf ages under DSR.Result showed that under DSR,the selective index of imazamox to JD 372、Jin Jing 818 at 1.5,2.5,3.5,4.5-leaf stage were less than 2,but the fresh weight inhibition rate of Jin Dao372,Jin Jing818 at 2.5 leaf stage under 25,50 g a.i./ha imazamox was less than or close to 10%,and the fresh weight inhibition rate of the weedy rice was more than 85%,revealed that 25-50 g a.i./ha imazamox can control weedy rice at 2.5 leaf stage Jin Dao372 and Jin Jing818 field.In order to further increase the safety of imazamox to imazamox-tolerant paddy,strong light and pellicular water were added for Jin Dao372 and Jin Jing818 herbs at 2.5 leaf stage after imazamox application.The results showed that the selectivity index of imazamox to Jin Dao372 and Jin Jing818 increased with strong light and pellicular water,and the selectivity index of Jin Dao372 was 2.18,which was higher than that of Jin Jing818,and reached relative safety.The sensitivity of common cultivated rice to imazamox were determined by whole plant bioassay method.The results showed that imazamox inhibitted seriously growth of japonica and indica rice,so attention should be paid to avoiding liquid drift and irrigation water crossfire when imazamox was applied,and the planting area of imazamox-tolerant paddy and common cultivated rice should be reasonably planned.In this chapter,the safety of soil residual toxicity of imazamox to barley,wheat,rapeseed and brassica chinensis was evaluated by field simulation experiment.The results showed that from the comprehensive evaluation of germination rate,plant fresh weight and plant height,the soil residual toxicity of imazamox inhibited the growth of afterreap crop significantly at 0 days after application,and the inhibitory effect of residual toxicity on them gradually weakened with the change of time.When the dosage of imazamox was 50 g a.i./ha,wheat,barley and rapeseed could be planted 4 months,7 months and 8 months after treatment respectively.When the dosage of imazamox was 100 g a.i/ha,wheat could be planted 5 months after treatment and barley could be planted 8 months after treatment.In the second chapter,based on the safety experiment of imazamox to imazamox-tolerant paddy,two plant growth regulators,Bihu and Yuehu,were selected to alleviate the toxicity of imazamox to JD 372,in order to solve the damage that 50、100 g a.i/ha imazamox to JD 372 were found in the experiment.The effects of different doses of Bihu,Yuehu and 50 、 100 g a.i./ha imazamox on the control effect of weedy rice were investigated.The results showed that the fresh weight inhibition rates were between 88%and 95%,which indicated that the mixed combinations of Bihu,Yuehu and imazamox had no effect on the control effect of the mixed combinations against weedy rice The mixed combinations of different doses of Bihu,Yuehu and 50、100 g a.i./ha imazamox were investigated to alleviate the toxicity of imazamox to Jin Dao372.The results showed that the mixture of 45g/ha Bihu and 50 g a.i./ha imazamox could significantly alleviate drug toxicity.The mixture of 450g/ha Yuehu and 50,100 g a.i./ha imazamox,and 900 g/ha Yuehu and 100 g a.i./ha imazamox could significantly alleviate the drug toxicity.To study the effect of topdressing Bihu and Yuehu on alleviating the drug harm caused by imazamox to Jin Dao372,the drug harm caused by imazamox to JD 372 was remitted by topdressing Bihu and Yuehu.The results showed that 90 g/ha Bihu and 450 g/ha Yuehu could significantly alleviate the toxicity of 50 g a.i./ha imazamox to JD 372 when leaf tip loss of greening was found after spraying with imazamox.The reason of the difference of tolerance between JD 372 and Weedy rice to imazamox was preliminarily revealed from the point of view of target enzyme ALS.By measuring the activity of ALS enzyme in vitro in JD 372 and Weedy Rice,we found that the decreased sensitivity of in vitro ALS to imazamox might be one of the reasons for the difference in tolerance.Through sequence alignment,we found that the mutation of amino acid 627 of ALS gene from Ser to Asn was one of the reasons for the difference in imazamox tolerance between JD 372 and Weedy Rice.Through q PCR,we found that the ALS gene expression levels of JD 372 and Weedy rice were significantly different at 24 h and 72 h,and the ALS gene of the former was significantly up-regulated,while the ALS gene of the latter was slightly changed.This suggested that the up-regulation of ALS gene might be one of the reasons why JD 372 was more tolerant to imazamox.