A kochia (Kochia scoparia) biotype resistant to triazine and ALS-inhibiting herbicides

Abstract

A kochia biotype from McDonough County, Illinois, was suspected to be resistant to both triazine and acetolactate synthase (ALS)-inhibiting herbicides. We performed greenhouse and laboratory experiments to confirm, quantify, and determine the molecular basis of multiple herbicide resistance in this biotype. Whole-plant phytotoxicity assays confirmed that the biotype was resistant to triazine (atrazine), imidazolinone (imazethapyr), and sulfonylurea (thifensulfuron and chlorsulfuron) herbicides. Relative to a susceptible kochia biotype, resistance to these herbicides ranged from 500- to > 28,000-fold. The kochia biotype from McDonough County also displayed high levels of resistance (2,000- to 9,000-fold) to ALS-inhibiting herbicides in in vivo ALS enzyme assays, indicating that resistance to these herbicides was site-of-action mediated. Results from chlorophyll fluorescence assays indicated that triazine resistance was also site-of-action mediated. Foliar applications of atrazine had little or no effect on photosynthesis in the resistant biotype, even when atrazine concentrations were 108-fold higher than needed to inhibit photosynthesis in the susceptible biotype. A region of the gene encoding the D1 protein of photosystem II and all of the open reading frame of the gene encoding ALS were sequenced and compared between the resistant and susceptible biotypes. Resistance to triazine and ALS-inhibiting herbicides in the kochia biotype from McDonough County was conferred by, respectively, a glycine for serine substitution at residue 264 of the D1 protein and a leucine for tryptophan substitution at residue 570 of ALS.

Acetolactate Synthase Target-Site Mutations and Single Nucleotide Polymorphism Genotyping in ALS-Resistant Kochia (Kochia scoparia)

“…The entire DNA sequences of the ALS gene was 2,270 bp. The deduced mature ALS protein consisted of 666 amino acids, encoded by 1,998 bp, which is in agreement with the earlier kochia ALS sequence AF094326 (Foes et al 1999). Sequence information for kochia ALS gene sequences deposited in GenBank are given in Appendix Table 1.…”

Acetohydroxyacid synthase mutations conferring resistance to imidazolinone or sulfonylurea herbicides in sunflower

“…Genes for resistance to AHAS-inhibiting herbicides are partially dominant in several genera (Sebastian et al 1989;Newhouse et al 1991;Hart et al 1993;Wright and Penner 1998;Foes et al 1999), with mutant homozygotes often being more resistant than heterozygotes. Because AHAS1-c205 mutant homozygotes (T/T) were more strongly resistant to herbicides than heterozygotes (C/T) in the IMISUN-2 × ZENB9 F 2 family, the introgression of resistant alleles (T) into wild-type (C/C) male and female inbred lines is necessary to produce T/T hybrids and maximize herbicide resistance in hybrids.…”

“…Typically, R genes for AHAS-inhibiting herbicides show partial or complete dominance (Sebastian et al 1989;Newhouse et al 1991;Hart et al 1993;Wright and Penner 1998;Foes et al 1999). The R gene identified by Bruniard and Miller (2001) from ANN-PUR showed partial dominance.…”

Mutations inALSconfer herbicide resistance in redroot pigweed (Amaranthus retroflexus) and Powell amaranth (Amaranthus powellii)

“…For example, corn (Fang et al 1992, CAA45117) and kochia [Kochia scoparia (L.) Schrad.] (Foes et al 1999) have the serine residue, whereas canola (Rutledge et al 1991, CAA34680) has a valine residue at this position.…”