Target-site Resistance Mechanism In Amaranthus Retroflexus L. To Imazethapyr

With the widespread use of chemical herbicides, the development of herbicide resistance becomesmore and more serious in China. Amaranthus retroflexus L. is a self-pollinated, common annual dicotweed and distributes widely in farmlands and gardens due to good environment adaption. The soybeanyield can be reduced by up to 20% due to the effect of A. retroflexus. Imazethapyr is a commonherbicide used to control dicot weed in soybean field. In recent years, imazethapyr control failure on A.retroflexus occurs frequently in China. The aims of the present study were to characterize the level ofimazethapyr resistance in A. retroflexus populations collected in Heilongjiang, Jilin, Anhui, Neimenggu,Xinjiang province in China, and to identify the biochemical and molecular basis of resistance. The mainresults are as follows:(1)The results of single dose imazethapyr to A. retroflexus: the inhibition ratio of fresh weightfrom 13-03, 13-17 and 12-39 A. retroflexus populations are under 20% comparing to 13-76 A.retroflexus population. The three populations are resistant to imazethapyr.(2)The results of dose-response to imazethapyr: the RI of 13-03, 13-17 and 12-39 A. retroflexuspopulations is above 10. Moreover, the RI of 12-39 and 13-17 is higher than 90, while the RI of 13-03 is14.51.(3)The results of in vitro ALS assay: ALS extracted from resistant A. retroflexus populationsshowed lower sensitivity to imazethapyr. The I50 ratio between resistant A. retroflexus populations 13-03,13-17, 12-39 and susceptible A. retroflexus population 13-76 is 14.83, 15.27, 268 respectively, whichindicated that the resistance was due to reduced ALS sensitivity to imazethapyr.(4)The results of molecular test: Through partial sequencing of the ALS, three distinct mutationswere found in different populations. In 13-03, GCT was replaced by GTT at 205(the number refers tothe ALS site in Arabidopsis thaliana), which resulted in the substitution of Ala by Val. In 13-17, ACCwas changed to AGC at 653, leading to the substitution of Ser by Thr. 12-39 possessed a TGG to TTGmutation, resulting in a Trp-574-Leu substitution.This study illuminated imazethapyr resistance in A. retroflexus populations in China. The resistancewas due to ALS target-site mutations resulting in an insensitive ALS.