Resistance Of Descurainia Sophia L. To Florasulam In Wheat Fields Of Huang-huai-hai Region

Flixweed（Descurainia Sophia L.）,one of the common malignmant weeds in wheat fields in China,is seriously harmful to wheat fields in the Huang-Huai-Hai region of China.Florasulam,a triazolopyrimidine sulfonamide systemic herbicide,developed by Dow Agricultural Sciences in the 1990s.It has high efficiency,low toxicity,high selectivity and so on.It is another important acetolactate synthase（ALS,EC2.2.1.6）inhibitor class herbicides widely used in wheat field control in China after tribenuron-menthyl.Since obtaining temporary registration in 2001 in China,it has been widely used in China’s wheat fields.Unfortunately,in recent years,flixweed was more difficult to be controlled with florasulam at recommended rate after this herbicide was continuously applied for several years.This situation has caused serious damage in yield and quality of wheat in the Huang-Huai-Hai region of China.The aims of the present study were to characterize the sensitivity of 46flixweed populations collected from Hebei,Shandong and Henan Province in China to florasulam.Furthermore,exploring the resistance levels of some populaitions to florasulam and the situation of mutations of genes in ALS conserved regions.Identifying the sensitivity to other acetolactate synthase（ALS）inhibitors and alternative herbicides in some flixweed populations.Meanwhile,screening effective herbicides through field trials.The main results were as follows:1.A single-dose screening test was used to identify the sensitivity to florasulam in all the46 flixweed populations.The application rate for treatment was 7.5 g a.i.ha^-1.In total,7populations were sensitive（S）,while 30 populations were resistant（R）to florasulam.The resistant levels to florasulam in 30 populations were characterised.The resistance index（RI）were arranging from 22.1-fold to 385.0-fold when compared with S population.2.The flixweed ALS gene fragments of 24 R populations and 3 S populations were amplified and sequenced.The analysis of nucleotide and deduced amino acid sequences showed that there are only 13 R populations found amino acid substitutions,there were five amino acid mutation forms including Pro-197-His（CCT-CAT）,Pro-197-Thr（CCT-ACT）,Pro-197-Ser（CCT-TCT）,Pro-197-Leu（CCT-CTT）and Trp-574-Leu（TGG-TTG）.Pro-197-Thr and Pro-197-Leu substitutions were found in the HB-2 population.what`s more,Pro-197-Thr and Trp-574-Leu substitutions were found in the SD-6 population.The determination of SD-6mutation frequency showed that 35%of the plants were mutated at position 197（Pro197Thr）,40%of the plants were mutated at position 574（Trp574Leu）,and 25%of the plants also had197th and th574 amino acid mutations（Pro197Thr and Trp574Leu）.3.Results from in vitro ALS assays indicated that the total ALS activity was similar between the S and R populations.However,ALS extracted from the plants of resistant populations（SD-6）was much less susceptible to florasulam in comparison to the sensitive population（SD-9）.The herbicide concentration resulting in 50%reduction of ALS activity(I<sub>50</sub>)was 138.3-fold greater than the S population.4.Whole-plant dose-response experiments were conducted to determine the sensitivity of the R populations which were different from ALS genes to other herbicides:nicosulfuron,MCPA-Na,fluroxypyr,carfentrazone-ethyl,isoproturon,pyroxsulam,imazethapyr,QYM102,QYM102+fluroxypr-mepthyl,carfentrazone-ethyl+MCPA-Na.The result showed that the resistant population SD-6 have evolved various high resistance to 3 herbicides:nicosulfuron,pyroxsulam and imazethapyr（RRR）.Non-mutant resistant population HN-7 and resistant population HN-9 which had Trp-574-Leu mutation developed resistance to nicosulfuron,pyroxsulam and imazethapyr（RR）.The Pro-197-Thr resistant flixweed population developed resisitance to nicosulfuron（RR）,and the Pro-197-His resistant flixweed population developed resisitance to nicosulfuron and imazethapyr（RR）.What`s more,the Pro-197-Ser resistant flixweed population developed resisitance to pyroxsulam（RR）.The experiments showed that all of these populations were sensitive to MCPA-Na,fluroxypyr,isoproturon,carfentrazone-ethyl QYM102,QYM102+fluroxypr-mepthyl and carfentrazone-ethyl+MCPA-Na.5.The field experiment showed that the biological activity of each herbicide against flixweed were QYM102+fluroxypr-mepthyl>carfentrazone-ethyl+MCPA-Na>carfentrazone-ethyl>QYM102>MCPA-Na>fluroxypyr>florasulam.This study characterized the resistance to florasulam in flixweed populations collected from wheat fields of wheat producing areas in the Huang-Huai-Hai region of China.Resistance mechanism studies had shown that the target-site based resistance was established as being due to an insensitive form of ALS,resulting from substitutions at Pro197 or Trp574in the ALS gene.The sensitivity of each resistant population to 10 herbicides showed that different mutant populations had different sensitivity to each herbicide.The field experiment showed that QYM102+fluroxypr-mepthyl,carfentrazone-ethyl+MCPA-Na,carfentrazone-ethyl and QYM102 had good control effect on various resistant populations.