Nr. Burgos et al., Amaranthus palmeri resistance and differential tolerance of Amaranthus palmeri and Amaranthus hybridus to ALS-inhibitor herbicides, PEST MAN SC, 57(5), 2001, pp. 449-457
Suspected imazaquin-resistant accessions of Amaranthus palmeri were studied
to determine the magnitude of resistance and cross-resistance to acetolact
ate synthase (ALS)-inhibiting herbicides and compare differential tolerance
of A palmeri and Amaranthus hybridus to ALS inhibitors. Five of seven A pa
lmeri accessions were resistant to imazaquin. The most imazaquin-resistant
accession, accession 7, also showed 74, 39 and 117 times higher resistance
than the susceptible biotype to chlorimuron, diclosulam and pyrithiobac, re
spectively. Resistance to imazaquin and cross-resistance to other ALS inhib
itors in A palmeri was due to a less-sensitive ALS enzyme. A palmeri was 70
times more tolerant to imazaquin than A hybridus. A palmeri was also seven
times more tolerant to pyrithiobac than A hybridus. Differences in ALS enz
yme sensitivity could not fully account for the high tolerance of A palmeri
to imazaquin compared to A hybridus. Both species were equally affected by
chlorimuron and diclosulam. (C) 2001 Society of Chemical Industry.