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Physiological and biochemical characterization of quinclorac resistance in a false cleavers (Galium spurium L.) biotype

Van Eerd, L.L., Stephenson, G.R., Kwiatkowski, J., Grossmann, K., Hall, J.C.
Journal of agricultural and food chemistry 2005 v.53 no.4 pp. 1144-1151
Galium spurium, herbicide-resistant weeds, biotypes, quinclorac, herbicide resistance, physiological transport, translocation (plant physiology), exudation, roots, metabolism, ethylene, abscisic acid, signal transduction
The physiological and biochemical basis for quinclorac resistance in a false cleavers (Galium spurium L.) biotype was investigated. There was no difference between herbicide resistant (R) and susceptible (S) false cleavers biotypes in response to 2,4-D, clopyralid, glyphosate, glufosinate-ammonium, or bentazon. On the basis of GR50 (growth reduction of 50%) or LD50 (lethal dose to 50% of tested plants) values, the R biotype was highly resistant to the acetolactate synthase (ALS) inhibitor, thifensulfuron-methyl (GR50 resistance ratio R/S = 57), and quinolinecarboxylic acids (quinclorac R/S = 46), resistant to MCPA (R/S = 12), and moderately resistant to the auxinic herbicides picloram (R/S = 3), dicamba (R/S = 3), fluroxypyr (R/S = 3), and triclopyr (R/S = 2). The mechanism of quinclorac resistance was not due to differences in [14C]quinclorac absorption, translocation, root exudation, or metabolism. Seventy-two hours after root application of quinclorac, ethylene increased ca. 3-fold in S but not R plants when compared to controls, while ABA increased ca. 14-fold in S as opposed to ca. 3-fold in R plants suggesting an alteration in the auxin signal transduction pathway, or altered target site causes resistance in false cleavers. The R false cleavers biotype may be an excellent model system to further examine the auxin signal transduction pathway and the mechanism of quinclorac and auxinic herbicide action.