| Echinochloa glabrescens is one of the malignant weeds in rice fields in China.In recent years,Echinochloa glabrescens has decreased susceptibility to ALS inhibitor herbicides such as penoxsulam.In order to clarify the resistance level and resistance mechanism of penoxsulam in rice field Echinochloa glabrescens,In this study,40 Echinochloa glabrescens populations from paddy fields in Jiangsu,Zhejiang,Anhui and Shanghai were used as experimental materials.The sensitivity to penoxsulam was determined by whole bioassay and the cross resistance and multiplicity of the penoxsulam-resistant Echinochloa glabrescens population were determined.Through the study of the ALS sensitivity,gene sequence and gene expression of the penoxsulam-resistant Echinochloa glabrescens population,it was found that the target enzyme played a definite role in the resistance.Through the study of the main metabolic enzymes Cyt P450s and GST,it is clear that metabolic enzymes play an important role in the resistance mechanism.The main results of this study are as follows:The sensitivity of the 40 Echinochloa glabrescens population to penoxsulam was determined by whole bioassay.The results showed that the Echinochloa glabrescens population JYJD-3 was the sensitive population with the ED50 value of 1.89 g a.i.ha-1 in Jiangdu County,Yangzhou City,Jiangsu Province.SHQP-6 and SHQP-3 were the more resistant populations in the Echinochloa glabrescens population in Qingpu District,Shanghai,with ED50 values of 32.10 and 20.89 g a.i.-ha-1,and its respectively resistance index compared with the sensitive population JYJD-3 was 16.98 and 11.05.Thus SHQP-6 and SHQP-3 produced moderate levels of resistance to penoxsulam.The sensitivity of SHQP-6 and SHQP-3 to 27 common herbicides was determined by whole bioassay The resistance of Echinochloa glabrescens was resistant to pyroxsulam and imazameth.The relative resistance of SHQP-6 was 4.58 and 7.77 times higher than that the sensitive population JYJD-3,The relative resistance of SHQP-3 was 4.04 and 6.89 times.SHQP-3 had a higher level of resistance to quinclorac and quintrione.The relative resistance of SHQP-3 was 37.56 and 51.74 times higher than that the sensitive population JYJD-3,and the resistance population SHQP-6 and SHQP-3 of the propyrisulfuron,metamifop,propanil,butachlo,pendimethalin and halauxifen-methyl are still sensitive.The sensitivity of the penoxsulam-resistant Echinochloa glabrescens population to ALS in vitro was studied:There was no significant difference in the in vitro activity of the ALS enzyme between the resistant population SHQP-6 and the sensitive population JYJD-3 without the addition of penoxsulam.At different doses of penoxsulam,the resistance and susceptibility of the Echinochloa glabrescens population at 0.0005 ?M began to be inhibited and the activity of the enzyme decreased rapidly with the increase of penoxsulam concentration,and the inhibition rate of ALS was above 85%at 0.05 ?M.The IC50 values of 0.003 and 0.0021 ?M the relative resistance multiple of 1.43.The DNA sequence encoding Echinochloa glabrescens ALS was amplified by PCR,and its length was 1820 bp,which was close to the full length.The fragment had no intron and encoded 606 amino acid residues.No resistance-related point mutations were found in SHQP-6 by comparing the ALS gene sequence of SHQP-6 with JYJD-3.The results showed that there was no significant difference in the expression of ALS gene between SHQP-6 and JYJD-3 in the sensitive population before the treatment with ALS gene by fluorescence quantitative PCR.The expression of ALS gene was increased at 3 and 5 days after penoxsulam treatment,and the expression level of ALS gene was 2.29 and 1.3 times higher than that of sensitive population.The synergistic effect of Cyt P450s inhibitor malathion,PBO and ABT on penoxsulam was determined by whole plant bioassay.The results showed that the ED50 value of the penoxsulam-resistant Echinochloa glabrescens population SHQP-6 after spraying malathion,PBO and ABT was from 32.10 g a.i.·ha-1 to 1.46,1.73 and 3.47 g a.i·-ha-1,respectively,and it is hypothesized that Echinochloa glabrescens is metabolically resistant to the presence of Cyt P450s in penoxsulam.The results showed that the cytochrome b5 of SHQP-6 was significantly higher than that of the sensitive population JYJD-3 after 2,3 and 5 days after treatment with penoxsulam.Before the treatment,the NADPH-P450 reductase activity of SHQP-6 was 0.0985 nmol·min-1 ·mg-1 pro.There was no significant difference with the sensitive population.The activity of NADPH-P450 reductase of SHQP-6 was increased by 97.36%compared with that of penoxsulam and significantly higher than that of JYJD-3 at 5 days after penoxsulam treatment.The GST specific activity of SHQP-6 was 2.4888 nmol·min-1 mg-1 pro before treatment,and there was no significant difference compared with the sensitive population.The GST activity of SHQP-6 was increased.And JYJD-3 increased only after 1 d and 11d after herbicide administration.The GST specific activity of SHQP-6 was 1.57 times of that of GST before treatment at 11 days after herbicide treatment,which was significantly higher than JYJD-3. |
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