Monochoria Korsakowii Resistance To Sulfonylurea Herbicides

Sulfonylurea herbicides are very popular for their high activity and low toxicity,weeds, however,easily develop resistance to this group of herbicides due to its single site of action. Monochoria korsakowii is a worst weed in rice fields in north China,it competes light,water and nutrition with the crop and reduces its yield and affects its quality.The biological characters of M.korsakowii Jilin paddy rice,its resistance mechanisms to sulfonylurea herbicides and herbicide usages were studied.Following results were obtained:1.Biological characteristics of M.korsakowii have been observed.M.korsakowii is one of worst weeds that continuously geminates in June and July.The population geminated in June brings about serious damage to the crop,that could produce 3000-6000 seeds per plant. The critical competing time starts 30 days after rice were transplanted;the critical competing density is 30 M.korsakowii per square meter.2.Whole plant bioassay revealed that resistant biotypes of M.korsakowii to sulfonylurea herbicides were identified in seven regions in Jilin province,with different resistance level to the herbicides.Liu he and Longjing biotypes had higher resistance to bensulfuron-methy,with resistance index of 13.7 and 12.2.Gong Zhuling,Yushu,Dehui,Jiaohe,Panshi biotypes had resistance indices ranging from 6.3 to 9.2.M.korsakowii in Litihe and Longjing have developed resistance to pyrazosulfuron-ethy,the resistant biotypes showed the same trend with bensulfuron-methy,with resistance index 8.4 and 8.3,other biotypes in Jilin province had resistance indices ranging from 5.2 to 6.2.The resistant biotypes also showed cross-resistance to bensulfuron-methy and pyrazosulfuron-ethy.3.The reduced sensitivity of acetolactate synthas(ALS) in M.korsakowii conferred resistance to sulfonylurea herbicides.The ALS activity in M.korsakowii grown in Liuhe county and Dehui city was measured.The activity of ALS in the resistant(R) biotypes was lower than in the susceptible(S) biotypes.In Liuhe county,the EC₅₀ values of bensulfuron-methy and pyrazosulfuron-ethy to ALS of R and S biotype were 15262.7 nmol/L, 237.6 nmol/L and 1152.8 nmol/L,165.2nmol/L,respectively in vitro.The R biotype was 64.2-fold resistant to bensulfuron-methy and 67.5-fold resistant to pyrazosulfuron-ethy.The LC₅₀ values of bensulfuron-methy and pyrazosulfuron-ethy to ALS of R and S biotype were 411.0 g ai/hm²,12.9 g ai/hm² and 225.2 g ai/hm²,8.0 g ai/hm² respectively in vivo.The R biotype was 31.9-fold resistant to bensulfuron-methy and 28.2-fold resistant to pyrazosulfuron-ethy.In Dehui City,the EC₅₀ values of bensulfuron-methy and pyrazosulfuron-ethy to ALS of R and S biotype were 10737.2 nmol/L,397.5 nmol/L and 10961.3 nmol/L,188.6 nmol/L respectively in vitro.The R biotype was 27.0-fold resistant to bensulfuron-methy and 58.1-fold resistant to pyrazosulfuron-ethy.The LC₅₀ values of bensulfuron-methy and pyrazosulfuron-ethy to ALS of R and S biotype were 234.3 g ai/hm², 17.6 g ai/hm² and 204.1 g ai/hm²,10.6g ai/hm² respectively in vivo.The R biotype was 13.3-fold resistant to bensulfuron-methy and 19.3-fold resistant to pyrazosulfuron-ethy respectively.4.DNA sequence of ALS gene was amplified,cloned and compared between resistant and susceptible M.korsakowii.The resistance mechanism of M.korsakowii to sulfonylurea herbicides was firstly studied at molecular level in home and abroad.Compared with susceptible biotypes,three mutations were identified in sulfonylurea herbicides-resistant M. korsakowii.The R biotype was found to have a Pro to His,a Met to Val,a Arg to His at amino position 197,200,388 respectively,as numbered relative to the protein sequence of Arabidopsis thaliana.The mutation at 197 sites was consistent with previous reports.It indicated that this mutation was likely the very reason of the resistance to sulfonylurea herbicides.5.Field experiments on the control of M.korsakowii were studied with other five non-sulfonylurea herbicides,penoxsulam,oxadiargyl,oxadiazoles,bentazone and MCPA.The results showed that they could control M.korsakowii effectively.Pot experiments revealed that M.korsakowii resistant to sufonylurea herbicides did not showcross-resistance with imazethapyr and penoxsulam,both of them demonstrated a better control on M.korsakowii.In conclusion,this paper resistance and its mechanism of M korsakowii to sulfonylurea herbicides were first conducted at the biological and molecular level in China.