| Weed chemical control in agricultural production can bring economic benefits,At the same time, weed resistance is becoming an increasingly serious problem. All weeds in paddy fields, barnyard grass is among the most noxious weeds in the world due to its superior biology and tremendous ecological adaptations, butachlor(chloroacetanilides) can be used for its control and officially registered in 1982 in China. Until now little is known about the resistance of this weed for the sustainable weed managements. Based on the collected from paddy field barnyardgrass in different areas of China as the main research object, this paper researched the biological characteristics of barnyardgrass and determined the resistance level of it to butachlor by using filter paper method and whole plant bioassay.Non-target resistance mechanisms about barnyardgrass to butachlor were explored from plant important metabolic enzyme glutathione-s-transferase(GSTs), protective enzyme(SOD, POD, CAT and GPX) and gibberellins contents of barnyardgrass, and its resistance to pretilachlor and metolachlor and herbicide usages were studied. The results are as follows:1. The relative resistance level of barnyardgrass to butachlor were confirmed in rice production areas in China. Butachlor resistance was measured by whole plant bioassay. The results showed that all the sampled populations have exhibited resistance to butachlor with relative resistance index(RI) of 1.01 to 10.61 except Ledong(V24)(the relatively sensitive population, ED50=160.07 g a.i/ha). Differences in sensitivity were determined using the logit model and the butachlor-resistance level of grass population Changchun(V7) were the highest with RI value of 10.61, following by Loudi(V17), Dongying(V8),Guangdongwuhua(V21), Guangdongmeixian(V20), Chongqing(V4) and Longchuan(V22)with RI values of 8.34, 7.15, 6.92, 6.68, 5.57, 5.19, respectively. Relative RI values in other barnyardgrass populations were evaluated below 5. Some plants of the populations were highly resistant to butachlor, other had developed low to moderate or moderat-high resistance. The resistant biotypes also showed cross-resistance to pretilachlor and metolachlor.2. Physiological and biochemical characteristics were compared between the relativesensitive and resistant butachlor barnyard grass biotypes. Different resistance indexes in the same area were obtained with the two methods but with identical trends. There were a considerable differences in the responses of the populations to butachlor. Under the condition of the non-competition, The plant height and fresh weight of sensitive biotype barnyardgrass is higher than resistant biotypes, but 1000-grain weight is lower than resistant populations.The GSTs relative activities in resistant barnyardgrass increased significantly after treated by butachlor, the maximum values of two resistance biotypes of barnyardgrass(V17and V7) were observed at 5 th and 7 th days, which were 1.58 and 1.63-fold, compared with the sensitive biotype(V24) respectively. It was induced that the one important reason of weeds had different sensitivity to butachlor was the difference of metabolizing mechanism of GSTs.At the barnyard grass seed germination period to 1-leaf stage, Exogenous GA3 could significantly induce an elongation in shoot length of relative sensitive populations,butachlor mixed with GA3 exhibited significant antagonism, and butachlor mixed with MET showed significant synergism on barnyardgrass. It was found that soluble sugar content and a-amylase activity in the resistant-butachlor barnyardgrass populations were significantly higher than the relative sensitive barnyardgrass population. We speculate the relative increasing of endogenous gibberellin contents in butachlor-resistant barnyardgrass populations in vivo may be the most direct reason of resistance.After treated by butachlor, the sensitive population suffered less oxidative stress effect,but butachlor-resistant barnyardgrass populations suffered more severe oxidative stress.There were an irregular variation about CAT and T-SOD activity between sensitive and resistant barnyardgrass biotypes. Butachlor has no direct impact on the activity of CAT and SOD. The increasing of GPX activity plays a major role at the early stage of resistant barnyardgrass, while POD plays a major protective effect at later stage.3. Some herbicides and mixtures were obtained by a screening test for the effectively control of resistant-butachlor barnyardgrass. The results showed that, anilofos, quinclorac,metolachlor or pyrazosulfuron-ethyl against V17 biotype had a poor control effects, there may be a multiple resistance phenomenon. Mixtures such as butachlor + oxadiazon,mefenacet + oxadiazon, penoxsulam + butachlor or penoxsulam + ethoxysulfuron can be selected as a part of herbicide sequences and rotations for the control of butachlor-resistant barnyardgrass. We recommend that the optimal proportional range was 10 g a.i./ha + 450-600 g a.i./ha(penoxsulam + butachlor), namely active ingredient proportion was 1:(45-60).In general, the resistant levels and distributions of barnyardgrass populations to butachlor and its cross-resistance of some populations to the same chemical classes of very-long-chain fatty acids(VLCFAS) inhibitors were confirmed in China. An evaluation criteria was put forward for the resistance level of barnyardgrass to butachlor in rice field based on fresh weight control effects under the recommended single rate. And some herbicides and mixtures were screened for the effectively control of resistant-butachlor barnyardgrass population. The non-target resistance mechanism of barnyardgrass to butachlor were revealed in enzyme and hormone level. There were a correlation between GAs and the formation of resistant-butachlor barnyardgrass populations. These results provide an important basis for prevention or control the formation and development of resistant-butachlor barnyardgrass populations and herbicides scientific use. |
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