| American sloughgrass (Beckmannia syzigachne) has become one of the most predominant and troublesome weeds in the wheat fields rotated with rice after twenty years of reduced-and no-tillage practices. Fenoxaprop-p-ethyl is one of the main post-emergence herbicides available to selectively control grass weeds in wheat fields in China. Fenoxaprop-p-ethyl was no longer as efficiency as it used to be, even failed to control American sloughgrass after many years successful control, which decreased the product of wheat greatly. This research aimed to1) investigate the resistant level and the resistant mechanism in American sloughgrass from partial regions in China,2) provide theoritical bases and guide for scientific control of American sloughgrass. The response to fenoxaprop-p-ethyl was tested in59American sloughgrass populations collected from Jiangsu province, Anhui province, Shandong province and Hubei province. The resistant mechanism in some populations was studied. The main results were as follows:(1) All the59populations were treated with fenoxaprop-p-ethyl at the rate of1×(62.1g ai ha-1),3x, and20x respectively by using whole-plant method. In the59populations tested,28populations were sensitive,17populations were slightly resistan,5populations were moderately resistant and10populations were highly resistant to fenoxaprop-p-ethyl. The resistant lelve of15populations were determined. All the15populations evolved obvious resistance to fenoxaprop-p-ethyl. The resistance index (RI) were7.7-615.4according to the susceptible population. The RI of AH-12population, JS-04population, JS-10population, JS-26population, JS-32population, JS-33population and SD-04population were615.4,260.8,157.4,565.0,257.5,445.0and236.8respectively. AH-12population collecting from Lujiang county, Anhui province showed higher resistance than others.(2) Whole-plant method was employed to determine the cross-resistance to clodinafop-propargyl, sethoxydim, clethodim, pinoxaden, pyroxsulam, mesosulfuron, flucarbazone-sodium and isoproturon in AH-12population, JS-26population, JS-32population, JS-33population and SD-04population. The results showed that all the populations tested were highly resistant to clodinafop-propargyl, with the RI294.2,19.4,279.1,1119.8and73.9for AH-12population, JS-26population, JS-32population, JS-33 population and SD-04population respectively. AH-12population, JS-33population and SD-04population showed23.1,28.4and14.5fold resistance to sethoxydim respectivley, JS-26population had a slight resistance to sethoxydim and JS-32populations was susceptible to sethoxydim. JS-33population and SD-04population showed6.1and5.4fold resistance to clethodim, JS-26population and JS-32population were slightly resistant to clethodim with the RI of2.6and2.5respectively. AH-12population was susceptible to clethodim. AH-12population, JS-26population and JS-32population showed45.0,45.9and15.8fold resistance to pinoxaden. JS-33population and SD-04population were only slightly resistant to pinoxaden (RI=3.8and2.4respectivley). All the five populations showed resistance to pyroxsulam with the RI of2.0,6.0,7.8,13.9and58.7. JS-33population and SD-04populations was highly resistant to pyroxsulam. JS-32population was susceptible to mesosulfuron. AH-12population was slightly resistant to mesosulfuron, while other populations tested showed moderate resistance to mesosulfuron. JS-26population and SD-04population were highly resistant to flucarbazone-sodium. JS-32population and JS-33population were slightly resistant to flucarbazone-sodium. AH-12population was compeletely killed by flucarbazone-sodium at the recommand rate (30.5g ai ha-1). Isoproturon killed all the populations tested at the recommand rate (1050g ai ha-1).(3) The activity of GSTs in different populations was determined by taking CDNB as the substrate. The GSTs activity in AH-12population, JS-04population, JS-26population and JS-32population was not induced more than the susceptible population after sprayed with fenoxaprop-p-ethyl at recommand rate. While the GSTs activity in JS-33and SD-04were highly enhanced by fenoxaprop-p-ethyl. The GSTs activity was enhenced about60%in SD-04population at the third day after treatment.(4) The activity of CYPs in resistant populations was investigated by comparing the control efficiency between fenoxaprop-p-ethyl and fenoxaprop-p-ethyl plus PBO. The results indicated that PBO only showed synergy in JS-33population and SD-04population.(5) The coding gene of CT domain from17populations were cloned, sequnced and aligned. An Ile178iLeu mutation caused by nucleotide change of ATA to TTA was found in JS-04population and JS-18population. The codon of position1999changed from TGG to TTG which resulted in an Trp1999Leu substitution in JS-26population. A Trp2027Cys substitution resulted from a TGG to TGC mutation was indentified in AH-12population. JS-15population, JS-31population and JS-32population were all observed containing an Ile2041Leu mutation which was caused by the codon change of ATT to AAT. The codon of position2078changed to GGT from GAT and resulted in the Asp2078Gly mutation in JS-33population. A Gly2096Ala change was found in SD-04population, which was caused by the GGC to GCC mutation.(6) A CAPS based method was developed by taking EcoR Ⅰ and Hae Ⅲ as digesting tools to analyze the Ile2041Asn and Gly2096Ala mutation respectively. A digesting site of Mae I was introduced by an inforeced base in primer, then the dCAPS was developed to detect the Trp2027Cys mutation.17mutant homozygotes,5hetrozygotes and109wild type plants were identified in JS-32population.16mutant homozygotes,39hetrozygotes and10wild type plants were identified in SD-04population.103mutant homozygotes,1hetrozygote and4wild type plants were identified in AH-12population.(7) A real-time quantification PCR method was built to analyze the difference of expression level of ACCase gene between the resistant population and susceptible population by employing the β-tubulin gene as the keep-house gene. The results indicated that there were no significant difference on the expression level of ACCase gene between the resistant population and susceptible population.The resistance to fenoxaprop-p-ethyl in American sloughgrass which were collected from wheat fields rotated with rice was preliminarily investigated in this paper. The different populations had different cross-resistance pattern. Some populations have evolved resistance to ALS inhibitors. The resistance to fenoxaprop-p-ethyl was endowed by the insensitive target enzyme resulted from a specific point mutation, or was endowed by the enhenced metabolism caused by the induced activity of GSTs or CYPs, even was endowed by two or more than two mechanisms. A rapid and accurate (d)CAPS method was developed to detect a point mutation cofferring resistance to fenoxaprop-p-ethyl. |
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