Cross-resistance pattern to four AHAS-inhibiting herbicides of tribenuron-methyl-resistant flixweed (Descurainia sophia) conferred by Asp-376-Glu mutation in AHAS

Abstract

Flixweed (Descurainia sophia L.) is a problematic and widespread weed in winter wheat fields and has been controlled by tribenuron-methyl for more than twenty years in China. In this study, a flixweed accession (HB25) with an Asp-376-Glu mutation in acetohydroxy acid synthase (AHAS) was identified and purified. The purified HB25 accession (pHB25) developed 758.1-fold resistance to tribenuron-methyl and exhibited obvious cross-resistance to four AHAS-inhibiting herbicides. The R/S ratios of GR 50 to herbicides of halosulfuron-methyl (SU), flumetsulam (TP), imazethapyr (IMI) and pyribenzoxim (PTB) were 346.1 15.7, 8.1 and 7.1, respectively. The reduced AHAS sensitivities to four different AHAS-inhibiting herbicides, which were caused by the Asp-376-Glu mutation, were responsible for the resistance and cross-resistance to AHAS-inhibiting herbicides. The R/S ratios of I 50 to tribenuron-methyl, halosulfuron-methyl, flumetsulam, imazethapyr and pyribenzoxim were 844.5, 532.9, 74.5, 13.3 and 5.5 respectively. The results of AHAS activity in vitro were highly correlated with that of whole-plant response experiments.

Effects of resistance mutations of Pro197, Asp376 and Trp574 on the characteristics of acetohydroxyacid synthase (AHAS) isozymes

“…Data are the mean ± standard error of two experiments. The data for the SD8, pHB24 (Pro197Thr) and pHB42 (Trp574Leu) subpopulations have been published before in Deng et al …”

“…Over the past few years, we have studied the biochemical and genetic bases of resistance and cross‐resistance in D. sophia and established that mutated AHAS and one or more cytochrome P450 enzymes conferred the D. sophia resistance to tribenuron‐methyl. Resistance mutations at sites Pro197 (substituted by Ser, Leu, Thr, His and Ala), Trp574 (Leu) or Asp376 (Glu) were identified in tribenuron‐methyl‐resistant D. sophia . Additionally, two mutated AHAS isozymes (with the Trp574Leu mutation in AHAS1 and the Pro197Thr mutation in AHAS2) were first identified in D. sophia .…”

Resistance mutations of Pro197, Asp376 and Trp574 in the acetohydroxyacid synthase (AHAS) affect pigments, growths, and competitiveness of Descurainia sophia L

“…At present, total seven resistance mutations were identified in AHAS isozymes at sites of Pro197 (Pro197Leu, His, Ser, Thr, Tyr), Asp376 (Asp376Glu) and Trp574 (Trp574Leu) in D. sophia populations 22 – 24 . In recent years, we have identified six out of seven mutations from more than sixty D. sophia populations.…”

“…Descurainia sophia L. is an annual and notorious broad-leaf weed infesting winter wheat, which has evolved extremely high resistance to SU herbicide tribenuron-methyl across China 20 – 22 . Our research confirmed the TSR and NTSR mechanisms conferred D. sophia resistance to tribenuron-methyl.…”

“…Our research confirmed the TSR and NTSR mechanisms conferred D. sophia resistance to tribenuron-methyl. Resistance mutations were identified at site of Pro197 (substituted by Ala, Leu, Thr, Ser, and His) or Asp376 (by Glu) or Trp574 (by Leu) in AHAS1 or (and) AHAS2 in tribenuron-methyl resistant D. sophia 22 – 24 . In addition, one or more cytochrome P450s mediated D. sophia resistance to tribenuron-methyl 25 .…”