CATCHWEED BEDSTRAW (Galium aparine) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: PROLINE 197 to LEUCINE
Catchweed Bedstraw (Galium aparine) is a dicot plant in the rubiaceae family. A single amino acid substitution from Proline 197 to Leucine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Catchweed Bedstraw

Chemical Family	Example Herbicide	Resistance Level
Imidazolinones	Imazethapyr	Intermediate Resistance < 10 fold
Pyrimidinyl benzoates	Bispyribac-Na	Intermediate Resistance < 10 fold
Sulfonylureas	Chlorsulfuron	Resistant > 10 fold
Triazolopyrimidine - Type 1	Chloransulam-methyl	Intermediate Resistance < 10 fold
Triazolinones	Flucarbazone-Na	Intermediate Resistance < 10 fold

NOTE

R/S ratios not quantified for all herbicides, but plants with this mutation survived 4x dose of one herbicide from each class. 

REFERENCES

Zhang, L. L., Q. Li, W. L. Guo, W. Li, and J. X. Wang. 2016. Molecular mechanism of Galium aparine resistance to tribenuron-methyl. Chinese Agricultural Science Bulletin 32 : 110 - 113.

In recent years,the tribenuron-methylin resistant Galium aparine was serious throughout HenanProvince,and common dose of tribenuron-methyl cannot control Galium aparine any more.The objective ofthis study is to understand the molecular mechanism of the Galium aparine resistance to tribenuron-methyl.Through total DNA extraction,ALS clone and sequencing,the authors found the specific mutation sites inamino acid sequence of acetolactate synthase(ALS) in the resistant biotype of Galium aparine.Compared withthe susceptible biotype,there were three types of amino acid substitutions in the resistant biotypes,of which,the amino acid substitution of Pro197(CCC) to Thr(ACC) and Pro197(CCC) to Leu(CTC) were located in thehighly conserved region Domain A,Thr 457(ACC) to Ser(TCC) in the non-conservative region.Thesubstitution of Pro197 might be the reason for the resistance in the R-biotype of Galium aparine to tribenuron-methyl..

Deng, W., Y. Di, J. Cai, Y. Chen, and S. Yuan. 2019. Target-site resistance mechanisms to tribenuron-methyl and cross-resistance patterns to ALS-inhibiting herbicides of catchweed bedstraw (Galium aparine) with different ALS mutations.. Weed Science 67 : 183 - 188.

Catchweed bedstraw (Galium aparine L.) is a problematic dicot weed that occurs in major winter wheat (Triticum aestivum L.) fields in China. Tribenuron-methyl has been widely used to control broadleaf weeds since 1988 in China. However, overuse has led to the resistance evolution of G. aparine to tribenuron-methyl. In this study, 20 G. aparine populations collected from Shandong and Henan provinces were used to determine tribenuron-methyl resistance and target-site resistance mechanisms. In dose–response experiments, 12 G. aparine populations showed different resistance levels (2.92 to 842.41-fold) to tribenuron-methyl compared with the susceptible population. Five different acetolactate synthase (ALS) mutations (Pro-197-Leu, Pro- 197-Ser, Pro-197-His, Asp-376-Glu, and Trp-574-Leu) were detected in different resistant populations. Individuals heterozygous for Pro-197-Ser and Trp-574-Leu mutations were also observed in a resistant population (HN6). In addition, pHB4 (Pro-197-Ser), pHB7 (Pro-197- His), pHB8 (Pro-197-Leu), pHB5 (Asp-376-Glu), and pHB3 (Trp-574-Leu) subpopulations individually homozygous for specific ALS mutations were generated to evaluate the cross- resistance to ALS-inhibiting herbicides. The pHB4, pHB7, pHB8, pHB5, and pHB3 subpopulations all were resistant to sulfonylurea, pyrazosulfuron-ethyl, triazolopyrimidine, flumetsulam, sulfonylamino-carbonyl-triazolinone, flucarbazone-sodium, pyrimidinyl thio- benzoate, pyribenzoxim, and the imidazolinone imazethapyr. These results indicated the diversity of the resistance-conferring ALS mutations in G. aparine, and all these mutations resulted in broad cross-resistance to five kinds of ALS-inhibiting herbicides..

This case was entered by Patrick Tranel Email: tranel@illinois.edu

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