Weed Technology

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Weed Technology 19(3):539-548. 2005
doi: 10.1614/WT-03-215R1.1

Imidazolinone-Resistant Wheat Acetolactate Synthase In Vivo Response to Imazamox1

CURTIS R. RAINBOLT, DONALD C. THILL, ROBERT S. ZEMETRA, and DALE L. SHANER2

2First author: Assistant Professor, Everglades Research and Education Center, University of Florida/IFAS, Belle Glade, FL 33430; second and third authors: Professor, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow, ID 83844-2339; fourth author: Plant Physiologist, USDA-ARS, Fort Collins, CO 80523-1325. Corresponding author's

Several experiments were conducted to evaluate the utility of an in vivo acetolactate synthase (ALS) assay for comparing sensitivity to imazamox among imidazolinone-resistant wheat cultivars/lines. Ten single-gene imidazolinone-resistant winter wheat cultivars/lines, one two-gene and four single-gene imidazolinone-resistant spring wheat cultivars/lines, and three pairs of heterozygous and homozygous imidazolinone-resistant winter wheat lines were evaluated in the assay experiments. Additionally, a dose-response assay was conducted to evaluate the tolerance of several imidazolinone-resistant wheat cultivars to imazamox on a whole plant level. The I50 value (i.e., the imazamox dose that inhibited ALS activity by 50%) of the winter wheat cultivar ‘Above’ was 54 to 84% higher than the I50 values of 99-420, 99-433, and CV-9804. However, based on the results of this study, it is unclear whether genetic background or market class (hard red winter vs. soft white winter) influences the level of ALS inhibition by imazamox. Teal 15A, the two-gene imidazolinone-resistant spring wheat cultivar, had an I50 value that was two to three times greater than the I50 value of the single-gene imidazolinone-resistant spring wheat cultivars/lines. The heterozygous imidazolinone-resistant wheat lines had I50 values that were 69 to 81% less than the I50 values of the homozygous lines. In the whole plant dose response, the R50 values (i.e., the imazamox dose that reduced biomass by 50%) of the susceptible cultivars Brundage 96 and Conan were 15 to 17 times less than the homozygous single-gene imidazolinone-resistant winter and spring cultivars/lines, whose R50 values were about 1.7 times less than the R50 value of the two-gene imidazolinone-resistant spring wheat line, Teal 15A. The results of the in vivo ALS imazamox assays and the whole plant imazamox dose-response assay were similar, indicating that the in vivo assay can be used to accurately and quickly compare resistance between imidazolinone-resistant wheat cultivars/lines.

Nomenclature: Imazamox, wheat, Triticum aestivum L.

Additional index words: Crop safety, herbicide tolerance, herbicide-resistant wheat, in vivo ALS assay.

Abbreviations: ALS, acetolactate synthase; CPCA, 1,1-cyclopropanedicarboxylic acid; I50, imazamox dose that inhibited ALS activity by 50%; KARI, keto-acid reductoisomerase; R50, imazamox dose that reduced biomass 50%.



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Figure 1. Example of SAS programming code using PROC NLMIXED for (A) the maximum likelihood dose-response model and I50 calculations and (B) single degree of freedom full dummy variable contrast

Figure 2. Estimated dose-response curve and actual data for Above, a single-gene homozygous resistant imidazolinone-resistant winter wheat cultivar in the in vivo ALS imazamox dose-response experiment

Figure 3. Estimated dose-response curves for imidazolinone-resistant winter wheat cultivars/lines in the in vivo ALS imazamox dose-response experiment

Figure 4. Calculated I50 values and upper and lower 95% confidence intervals for imidazolinone-resistant winter wheat cultivars/lines in the in vivo ALS imazamox dose-response experiment

Figure 5. Estimated dose-response curves for imidazolinone-resistant spring wheat cultivars/lines in the in vivo ALS imazamox dose-response experiment

Figure 6. Calculated I50 values and upper and lower 95% confidence intervals for imidazolinone-resistant spring wheat cultivars/lines in the in vivo ALS imazamox dose-response experiment

Figure 7. Estimated dose-response curves for imidazolinone-resistant heterozygous and homozygous winter wheat lines in the in vivo ALS imazamox dose-response experiment

Figure 8. Calculated I50 values and upper and lower 95% confidence intervals for imidazolinone-resistant heterozygous and homozygous winter wheat cultivars/lines in the in vivo ALS imazamox dose-response experiment

Figure 9. Estimated dose-response curves for wheat cultivars/lines in the whole plant imazamox dose-response assay experiment

Figure 10. Calculated R50 values and upper and lower 95% confidence intervals for cultivars/lines used in the whole plant imazamox dose-response assay experiment

table

Table 1. Market class, acetolactase synthase (ALS) resistance gene, and recurrent parent of imidazolinone-resistant cultivars/lines in the winter wheat and spring wheat in vivo ALS imazamox dose-response experiments and the whole plant imazamox dose-response experiment

table

Table 2. Parental information, resistance trait expression, and recurrent parent of winter wheat cultivars/lines in the heterozygous-homozygous and maternal-paternal parent in the in vivo acetolactase synthase imazamox dose-response experiment

table

Table 3. Model parameter estimates and standard errors for winter wheat cultivars/lines in the in vivo acetolactase synthase imazamox dose-response experiment

table

Table 4. Model parameter estimates and standard errors for spring wheat cultivars/lines in the in vivo acetolactase synthase imazamox dose-response experiment

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Table 5. Model parameter estimates and standard errors for homozygous and heterozygous imidazolinone-resistant cultivars lines in the in vivo acetolactase synthase dose-response experiment

table

Table 6. Model parameter estimates and standard errors for cultivars/lines in the whole plant imazamox dose-response experiment

Received for publication September 12, 2003, and in revised form May 6, 2005. Published with approval of the Agricultural Experiment Station, University of Idaho, as journal article 03741.

Wallac 1420 Victor3, Perkin Elmer Life and Analytical Sciences, Inc., 549 Albany Street, Boston, MA 02118-2512.

Cited by

Todd A. Gaines, W. Brien Henry, Patrick F. Byrne, Philip Westra, Scott J. Nissen, Dale L. Shaner. (2008) Jointed Goatgrass (Aegilops Cylindrica) by Imidazolinone-Resistant Wheat Hybridization under Field Conditions. Weed Science 56:1, 32-36
Online publication date: 1-Jan-2008.

Abstract & References : Full Text : PDF (157 KB) 

Arron H. Carter, Jennifer Hansen, Thomas Koehler, Donald C. Thill, Robert S. Zemetra. (2007) The Effect of Imazamox Application Timing and Rate on Imazamox Resistant Wheat Cultivars in The Pacific Northwest. Weed Technology 21:4, 895-899
Online publication date: 1-Oct-2007.

Abstract & References : Full Text : PDF (150 KB) 

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