Abstract
AbstractPennsylvania smartweed [Persicaria pensylvanica(L.) M. Gómez] is a common weed of rice (Oryza sativaL.) in the midsouthern United States and has recently become a concern for farmers because of reduced tillage systems. Acetolactate synthase (ALS) inhibitors have been extensively used for controlling smartweeds in imidazolinone-resistant and conventional rice. In the present study, we confirmed resistance to commonly used ALS inhibitors in rice and characterized the underlying resistance mechanism in aP. pensylvanicabiotype from southeast Missouri. A dose–response experiment was conducted in the greenhouse using bensulfuron-methyl, imazethapyr, and bispyribac-sodium to determine the resistance index (resistance/susceptibility [R/S]) based on GR50estimates. The target-siteALSgene was amplified from R and S plants, and sequences were analyzed for mutations known to confer ALS-inhibitor resistance. TheP. pensylvanicabiotype in question was found to be resistant to bensulfuron-methyl (R/S=2,330), imazethapyr (R/S=12), and bispyribac-sodium (R/S=6). Sequencing of theALSgene from R plants revealed two previously known mutations (Pro-197-Ser, Ala-122-Ser) conferring resistance to sulfonylureas and imidazolinones. This is the first report of ALS-inhibitor resistance inP. pensylvanica.
Highlights
Gómez], a member of the knotweed family (Polygonaceae), is a summer annual broadleaf weed distributed throughout the United States
Potential yield losses of up to 20% were reported in corn (Zea mays L.) (Sankula and Gianessi 2003)
Due to its rapid growth rate, high fecundity, complex dormancy, and irregular germination, P. pensylvanica continues to spread to new agricultural production regions (Askew and Wilcut 2002; Neubauer 1971)
Summary
The most commonly identified mechanism for resistance to ALS inhibitors is target-site based, due to a missense mutation in the ALS enzyme resulting in herbicide insensitivity (Tranel and Wright 2002). Target-site mutations conferring ALS resistance have been reported at eight locations (based on amino acid sequence from Arabidopsis) spread over five different domains (A to E) in the ALS gene (Boutsalis et al 1999; Devine and Eberlein 1997). Gene-specific primers from Amaranthus (Diebold et al 2003) and Russian-thistle (Salsola tragus L.) (Warwick et al 2010) were initially used to amplify and sequence the 3′ region of the ALS gene (630 bp) containing the Trp-574 amino acid site, previously associated with ALS-inhibitor resistance in weeds (Table 1).
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