Investigation of Multiple-Resistance and Molecular Characterization of Fenoxaprop-Resistance in Chinese Sprangletop (Leptochloa chinensis L. Nees)

Abstract

According to paddy field observations in 2002, fenoxaprop-ethyl resistance in have been found Chinese sprangletop (Leptochloa chinensis) at the Saphan-Sung district of Bangkok during 2540-2545. Whole-plant response in greenhouse tests, the resistance index of resistant-Chinese sprangletop was 10-25 fold higher than that of the susceptible one. The farmers were suggestel to change the herbicides used to control the Chinese sprangletop with a different mode of action from fenoxaprop-ethyl. In 2004, a second investigation by interviewing the farmers sites was carried at the same, out to ascertain the current situation of resistant-Chinese sprangletop. It was found that the farmers were satisfied with the action of changing the type of herbicide, because the resistant-Chinese sprangletop had apparently decreased. In addition, the resistant-Chinese sprangletop did not exhibit the multiple resistant to oxadiazon, propanil and quinclorac. To investigate the molecular basis of fenoxaprop-resistance in Chinese sprangletop, acetyl-CoA carboxylase (ACCase) gene encoding 657 bp of carboxyl transferase (CT) domain of Chinese sprangletop was isolated. The ACCase sequence of the resistant (R)- and the susceptible (S)-Chinese sprangletop were deposited in the genbank database with accession numbers AY803783 and AY662693, respectively. Based on the sequence data, four point mutations of nucleotides were detected in the R-Chinese sprangletop that lead to the substitutions of four amino acids (Phe¹⁷¹⁸ changed to Ser, Glu¹⁷³⁹ changed to Asp, Gly¹⁷⁴⁶ changed to Ala, and Ala¹⁸¹⁵ changed to Thr). It is possible that the point mutations may contribute to the molecular modification of the target site (ACCase gene) and caused the resistance to fenoxaprop-ethyl in the R-Chinese sprangletop. In addition, the accumulation of ACCase mRNA was detected in the same levels in both of the R- and the SChinese sprangletop. The results suggested that the molecular basis of resistance to fenoxaprop-ethyl in Chinese sprangletop may have occurred after the transcription of ACCase gene. Although, the expression slightly deceased in both of the R- and the S-biotypes, when treated with the recommended amount of fenoxaprop-ethyl (at 6.75 g a.i./ rai).