1 November 2009 Molecular Analysis of Hexazinone-Resistant Shepherd's-Purse (Capsella bursa-pastoris) Reveals a Novel psbA Mutation
Alejandro Perez-Jones, Suphannika Intanon, Carol Mallory-Smith
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A population of shepherd's-purse suspected to be resistant to the triazinone herbicide hexazinone, a photosystem II (PS II) inhibitor, was collected from an alfalfa field in 2007 in Oregon. A whole-plant, dose–response assay confirmed that the putative-resistant population was highly resistant to hexazinone. The resistant population was 22-fold more resistant to hexazinone than the susceptible population. However, the hexazinone-resistant population was susceptible to other PS II-inhibiting herbicides, including atrazine, diuron, and terbacil. DNA sequence analysis of the chloroplast psbA gene encoding the D1 protein of PS II, the target site of PS II inhibitors, identified a point mutation from Phe to Ile at position 255 in the hexazinone-resistant population. Single- and double-point mutations at position 255, which is located in the QB binding niche of the D1 protein, were previously reported in Chlamydomonas reinhardtii, Synechococcus species, and Synechocystis species after site-directed mutagenesis and were associated with decreased binding of PS II inhibitors. To our knowledge, this is the first report of a mutation of the psbA gene at Phe255 in a field-selected, herbicide-resistant plant.

Nomenclature: Atrazine; diuron; hexazinone; metribuzin; terbacil; alfalfa, Medicago sativa L. MEDSA; shepherd's-purse, Capsella bursa-pastoris (L.) Medik CAPBP.

Alejandro Perez-Jones, Suphannika Intanon, and Carol Mallory-Smith "Molecular Analysis of Hexazinone-Resistant Shepherd's-Purse (Capsella bursa-pastoris) Reveals a Novel psbA Mutation," Weed Science 57(6), 574-578, (1 November 2009). https://doi.org/10.1614/WS-09-089.1
Received: 26 May 2009; Accepted: 1 July 2009; Published: 1 November 2009
PS II inhibitors
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