Amaranthus blitoides S. Watson (prostrate pigweed) populations resistant to acetolactate synthase (ALS; EC 22.214.171.124)-inhibiting herbicides and triazines (SuR/TR) were found in Israel. The Ganot population was 6- to 790-fold more resistant to ALS inhibitors than the wild type due to an altered target site. Molecular analyses showed that the Ganot population was a mixture of two biotypes: (i) SuRA/TR in which domain A of the als gene differed in one nucleotide, resulting in substitution of Pro by Ser 188; (ii) SuRB/TR in which a mutation in domain B led to a substitution of Trp by Leu 569. The mutation in domain A resulted in resistance to all ALS inhibitors except imidazolinones, whereas the mutation in domain B led to resistance to all ALS inhibitors tested. SuRA/TR and SuRB/TR are multiple-resistant with an additional single mutation in the plastidic psbA gene that changes Ser 264 to Gly in the D1 protein, leading to triazine resistance. It is evident that plants within a population exposed to a similar selection pressure may show different patterns of cross-resistance due to three different point mutations. This unique phenomenon renders planning of rational weed management difficult or even impossible.
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Acknowledgments The assistance of Dr. Martha Stankiewicz is appreciated. This study was supported by the Deutsche Fors-chungsgemeinschaft, as a part of the Trilateral German–Israeli– Palestinian Research Program: Alternative Practices in Near East Agriculture for Environmental Conservation. We also thank the support given by the Chief Scientist Fund of the Ministry of Agriculture, Israel.
- Acetolactate synthase inhibitors
- Herbicide resistance