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Terbacil and Bromacil Cross-Resistance in Powell Amaranth (Amaranthus powellii)

Rick A. Boydston and Kassim Al-Khatib
Weed Science
Vol. 40, No. 4 (Oct. - Dec., 1992), pp. 513-516
Stable URL: http://www.jstor.org/stable/4045240
Page Count: 4
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Terbacil and Bromacil Cross-Resistance in Powell Amaranth (Amaranthus powellii)
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Abstract

A triazine-resistant Powell amaranth biotype collected in Idaho was approximately six times more resistant to terbacil and sixteen times more resistant to bromacil than a normal susceptible biotype when planted into terbacil- or bromacil-treated soil. The concentration of terbacil required to reduce photosystem II activity by 50% (I₅₀) in isolated thylakoids was 0.24 and 13.33 μM for the susceptible and resistant biotypes, respectively. Likewise, the I₅₀ values for bromacil were 0.33 and 18.4 μM for the susceptible and resistant biotypes, respectively. More ¹⁴C-terbacil was bound to isolated thylakoids of the susceptible than the resistant biotype with binding constants $({\rm K}_{{\rm b}})$ of 0.26 and 12.9 μM, respectively, indicating that resistance was at the chloroplast level.

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