Resistance Of Ammannia Arenaria To Bnsulfuron-Methyl And Its Molecular Echanism

Ammannia arenaria is one of the most harmful weeds in paddy rice fields in China, and itsoccurrence area is expanding rapidly in recent years. The effect of the weed controlled withbensulfuron-methyl(BSM) is less useful. But levels, populations and mechanism of the resistance of A.arenaria to BSM have not been reported worldwide. The experiments were conducted to determine theresistant levels of A. arenaria to bensulfuron-methyl, and further to ascertain the resistant mechanism.The results of the study as follows are useful for the risk assessment and effective control of theresistant A.arenaria.1. The resistant levels of different biotypes of A.arenaria to BSM, collected from Zhejiang provinceand Anhui province, were investigated by the agar method. For the99biotypes tested,94.9%ofthem were resistant to BSM, of which the percentages of the low resistance (3<Resistance index,RI≤10), the middle resistance (10＜RI≤50) and the high resistance (RI＞50) were26.3%,49.5%and19.2%, respectively. The RI of biotype NB0143-01(from Ningbo) and SX077(from Shaoxing)were as high as124.4and120.4, respectively. These results indicated that the A. arenaria werehighly resistant to bensulfuron-methy in paddy rice field, and were higher spread in Zhejiangprovince and Anhui province.2. The resistance levels of A. arenaria biotypes to BSM in regions of Zhejiang and Anhui provincewere investigated. It was different that the RI of A. arenaria biotypes collected from the Ningbo、Shaoxing、Hangzhou、Jiaxing and Huzhou cities in Zhejiang province and the Guangde city inAnhui province. The biotypes from Shaoxing were most resistant to BSM with the average RI of53.1; the biotypes from Ningbo took second place with the average RI of35.1; that from Huzhou,Hangzhou, Jiaxing and Guangde were less resistant to BSM, with the average RI of24.1,19.9,18.7and16.4, respectively. The main reason for this difference is related to the selection pressure ofBSM to A. arenaria. The longer time of the herbicide continuous used, the higher resistance levelwas investigated.3. This is the first report that the full length gene sequence of BSM target enzyme acetohydroxyacidsynthase (ALS) of A.arenaria in paddy rice field has obtained. The molecular biology techniqueswere used to analyze the ALS genes of A.arenaria resistance biotype AH014(Anhui, GuangDe)and sensitive biotype HZ001(Zhejiang, Hangzhou).The results showed that the full DNA sequencelength were2235bp and no introns, encoding667amino acids. Comparison with BLAST software,the full length amino acid sequence of A.arenaria is similar to cruciferous Descurainia Sophia and compositae Conyza canadensis with the highest86%similarity. These results indicated that theA.arenaria ALS genes and those coded ALS amino acid sequence were correct.4. The resistance mechanism of A. arenaria to BSM has been clear that ALS gene mutation is theimportant cause. ALS genes of Arabidopsis thaliana as reference frame were compared with thoseof A. arenaria resistant biotype AH014by MegAlign function module of the DNA Lasergenesoftware. The results showed that the197th of ALS amino acid sequence has mutated by proline(Pro) replaced by serine (Ser) which is the main resistance mechanism. This was the first reportabout the molecular mechanism of A. arenaria resistance to bensulfuron-methyl.