| Echinochloa crus-galli var.crus-galli,E.glabrescens and E.crus-galli var.mitis are serious weed species in rice fields in China,which frequently evolve herbicide-resistance.Penoxsulam is a safe,efficient,broad-spectrum herbicide widely used in rice fields,which is one of acetolactate synthase(ALS)inhibitor herbicides.Recently,some farmers complained some Echinochloa weed species showed insensitive to penoxsulam.This study aims to confirm the resistance of the 3 Echinochloa weed species to penoxsulam.Whole-plant bioassay experiments were conducted to determine the sensitivity of 52 E.crus-galli var.crus-galli populations,35 E.glabrescens populations and 29 E.crus-galli var.mitis populations to penoxsulam,and these populations were collected from 8 rice planting areas in China.After that,12 populations with various resistance levels to penoxsulam were studied to determine their sensitivities to other 13 herbicides frequently used in rice fields.Main results are:Among 52 tested E.crus-galli var.crus-galli populations,3 populations were susceptible to penoxsulam,with R/S ratios(ED50 value ratio of resistant population to susceptible one)lower than 2,and 4 populations showed decreased sensitivity with R/S ratios lower than 4 but higher than 2,5 populations were lowly resistant to penoxsualm with R/S ratios higher than 4 but lower than 10,7 populations were moderately resistant to penoxsulam with R/S ratios higher than 10 but lower than 30,20 populations were highly resistant to penoxsulam,whose R/S ratios were higher than 30 but lower than 150,and 13 populations held very high resistance to penoxsulam,with R/S ratios higher than 150.The population YB32 collected from Jiangsu was the most susceptible to penoxsulam,and the ED50 value was 0.08 g a.i./ha.The population YB14 collected from Heilongjiang was the most resistant to penoxsulam with an ED50 value of 102.36 g a.i./ha,and the R/S ratio was as high as 1279.50.Among the 35 E.glabrescens populations,3 populations were susceptible to penoxsulam,1 population showed decreased sensitivity to penoxsulam,5 populations were moderately resistant to penoxsulam,16 populations were highly resistant to penoxsulam,and 10 populations held very high resistance to penoxsulam.The population YF22 collected from Jiangsu was the most susceptible to penoxsulam with an ED50 value of 0.06 g a.i./ha.The population YF20 collected from Jiangsu was the most resistant to penoxsulam with an ED50 value of 17.74 g a.i./ha,and the R/S ratio was as high as 277.22.Among the 29 E.crus-galli var.mitis populations,1 population was susceptible to peoxsulam,and 1 population showed decreased sensitivities to penoxsulam,6 populations were lowly resistant to penoxsulam,3 populations were moderately resistant to penoxsulam,8 populations were highly resistant to penoxsulam,and 10 populations held very high resistance to penoxsulam.The population WM26 collected from Jiangsu was the most susceptible to penoxsulam,and the ED50 value was 0.03 g a.i./ha.The population WM29 collected from Ningxia was the most resistant to penoxsulam,with an ED50 value of 38.28 g a.i./ha,and the R/S ratio was as high as 1147.13.All of the 7 penoxsulam-resistant E.crus-galli var.crus-galli populations had evolved resistance to bispyribac-sodium and oxadiazon,with R/S ratios higher than 11 and 6,respectively.The R/S ratios of 7 penoxsulam-resistant populations to oxaziclomefone were lower than 5,while their ED50 values were all higher than recommended high dose.Most penoxsulam-resistant E.crus-galli var.crus-galli populations tested held resistance to quinclorac,metamifop,cyhalofop-butyl and pretilachlor,and the R/S ratio of YB14 population to quinclorac reached to 594.73.While the average R/S ratios were lower than 5 for the tested penoxsulam-resistant E.crus-galli var.crus-galli populations to pendimethalin,butachlor,oxyfluorfen,fenoxaprop-P-ethyl and pyribenzoxim.The penoxsulam-resistant E.glabrescens population YF01 was only resistant to oxaziclomefone among the 13 tested herbicides,whose ED80 value was 251.2%of recommended high dose.The penoxsulam-resistant E.crus-galli var.mitis population WM18 was moderately resistant to quinclorac,and fenoxaprop-P-ethyl,as well it held obvious resistance to oxaziclomefone,with an ED50 value higher than recommended high dose.E.crus-galli var.crus-galli,E.glabrescens and E.crus-galli var.mitis had showed obvious resistance to penoxsulam.Furthermore,some of penoxsulam-resistant populations of E.crus-galli var.crus-galli and E.crus-galli var.mitis had evolved multiple resistance to other herbicides.It's noteworthy that this study confirmed the resistance to pretilachlor,oxadiazon and oxaziclomefone in weeds for the first time in the world.As well,we firstly reported herbicide resistance in E.glabrescens,which is a common weed species in rice fields in China. |
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