Resistance and its resistant molecular mechanism ofAmmannia arenaria to ALS inhibiting herbicides

In recent years, Ammannia arenaria H.B.K. has become seriously harmful weed in paddy fields in the lower reach of Yangtze River plain. The resistance level of the biotypes of A. arenaria to four groups of ALS inhibiting herbicides including bensulfuron-methyl (BSM) were investigated by the method of seedling treatment. The DNA sequence and the expression of the ALS gene of the weed were analyzed with fluorescence quantitative PCR technique. The results showed that the resistance index (RI) of four A. arenaria biotypes including JX110 (Jiaxing, Zhejiang), JS039 (Suzhou, Jiangsu), NB0143-05 (Ningbo, Zhejiang) and AH014 (Guangde, Anhui) to BSM were 67.90, 17.59, 44.63 and 8.37, respectively. The biotypes exhibiting medium or high levels of resistance to BSM had evolved low level resistance to penoxsulam, bispyribac-sodium and imazethapyr. The full length sequence (2 235 bp) of the ALS gene which codes for 667 amino acids was cloned. Only the 93th leucine was substituted by proline in the amino acid sequence of the variable region of ALS in those three resistant biotypes including NB0143-05. However, the susceptibility of ALS enzyme from the biotype NB0143-05 to BSM decreased (RI 37.04) significantly, and its ALS gene expression was 1.86 times higher than that of sensitive biotype (HZ001) as induced by BSM. This indicated that the susceptibility decreasing of ALS enzyme to herbicide and the significant increasing of ALS gene expression after BSM induction might contribute to the resistance of A. arenaria (NB0143-05) to ALS inhibiting herbicides.