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EASTERN BLACK NIGHTSHADE (Solanum ptycanthum)
with GROUP B/2 resistance: (ALS INHIBITORS)
Inhibition of acetolactate synthase ALS (acetohydroxyacid synthase AHAS)

MUTATION: ALANINE 205 to VALINE

Eastern Black Nightshade (Solanum ptycanthum) is a dicot plant in the solanaceae family. A single amino acid substitution from Alanine 205 to Valine has led to resistance to ALS inhibitors as indicated in the table below.

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Eastern Black Nightshade

Chemistry	Example	Resistance
Imidazolinones	Imazethapyr	Resistant > 10 fold
Pyrimidinylthiobenzoates	Bispyribac-Na	Not Determined
Sulfonylureas	Chlorsulfuron	Intermediate Resistance < 10 fold
Triazolopyrimidines	Chloransulam-methyl	Susceptible
Sulfonylaminocarbonyltriazolinone	Flucarbazone-Na	Not Determined

NOTES

REFERENCES

Ashigh, J. and F. J. Tardif (2007). An Ala205Val substitution in acetohydroxyacid synthase of eastern black nightshade (Solanum ptychanthum) reduces sensitivity to herbicides and feedback inhibition. Weed Science , 55 (6) : 558-565.

Twelve populations of eastern black nightshade from different locations in Ontario are resistant to imazethapyr. This study aimed at determining the molecular basis of resistance in these populations and the activity of the resistant acetohydroxyacid synthase (AHAS) enzyme compared to that of the sensitive AHAS in response to different herbicides and branched-chain amino acid concentration. The results of partial AHAS sequencing indicated that all resistant populations had a cytosine331 to thymine substitution coding for an alanine205 to valine substitution. In vitro AHAS enzyme assays of one resistant population showed that the specific activity of the resistant enzyme was 56% less than that of the susceptible enzyme. AHAS from the resistant population was 72-, 70-, and 64-fold less sensitive than that of the susceptible population to imazethapyr, imazamox, and primisulfuron, respectively. Furthermore, the resistant enzyme was less sensitive to feedback inhibition from branched-chain amino acids compared to the susceptible enzyme. Results confirmed that resistance in resistant populations of eastern black nightshade was conferred by target-site modification and that the Ala205Val substitution alters the kinetics and regulation of branched-chain amino acid biosynthesis.