Characteristics of Atrazine-Resistant Biotypes of Three Grass Weeds

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Abstract
Three triazine-resistant biotypes of grass weeds, hood canarygrass (Phalaris paradoxa L. # PHAPA), ryegrass (Lolium rigidum Gaud.), and slender foxtail (Alopecurus myosuroides Huds. # ALOMY) were collected along roadsides on the coastal plain of Israel that had been treated repeatedly with s-triazine herbicides. Resistant biotypes (R) survived up to 4 kg ai/ha of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] applied pre-and postemergence, while susceptible (S) biotypes were killed by 0.25 kg/ha. R and S biotypes were equally sensitive to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea]. Electron transport in chloroplasts isolated from R biotypes was not affected by atrazine, whereas in S biotypes electron transport was inhibited 50% by 0.4 to 1.0 μM atrazine. Chloroplasts from both biotypes were equally sensitive to diuron. These data indicate that the R biotypes have a plastidic mode of resistance to atrazine. In addition, seedlings of R biotypes exhibited resistance to triazinone herbicides. The R biotype of hood canarygrass was more tolerant to postemergence application of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}.