Characterization of ans-Triazine-Resistant Biotype ofBrachypodium distachyon

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Abstract
A triazine-resistant (R) biotype of a Graminaceous weed,Brachypodium distachyon(= Trachynia distachya), was found in the lower Galilee area of Israel after repeated treatments of roadsides with simazine [2-chloro-4,6-bis (ethylamino)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. It was not affected at levels up to 3.0 kg/ha of soil-incorporated atrazine or simazine. The (R) biotype was unaffected by atrazine, as ascertained by measuring whole-leaf and plastid fluorescences and the Hill reaction. The triazine-sensitive (S) biotype was inhibited in all these reactions. The data suggest that the (R) biotype has a plastid mode of resistance common to many weed species. The (R) biotype metabolized14C-(ring)-atrazine more rapidly to both water-soluble and to chloroform-soluble compounds than the (S) biotype did, but that could not explain the immediate resistance at the plastid level. Probably there was evolution towards increased tolerance by detoxification as well as plastid level resistance.