Seed soaking method to test resistance in Raphanus raphanistrum to ALS-inhibiting herbicides

Abul Hashem and David G. Bowran, Centre for Cropping Systems, Department of Agriculture, PO Box 483, Northam, Western Australia 6401, Australia.


Testing resistance in Raphanus raphanistrum to ALS-inhibiting herbicides takes 10 weeks using conventional method where seedlings are raised from collected seeds and sprayed with herbicides. The aim of this study was to develop a reliable method to test for resistance in R. raphanistrum populations to ALS-inhibiting herbicides without requiring a foliar spray. Germinable seeds of R. raphanistrum were soaked in solutions of ALS-inhibiting herbicides for 24 hours and then sown in pot soil. A 40 mg L-1 triasulfuron (714 g a.i. kg-1), 10 mg L-1 metosulam (714 g a.i. kg-1), and 20 mg L-1 chlorsulfuron (750 g a.i. kg-1) were found to be the best concentrations for screening of the resistant biotypes within the

R. raphanistrum populations tested in this study. At these concentrations, plants of the susceptible biotypes and susceptible plants within resistant biotypes died or remained in a severely stunted condition often without producing a true leaf, while most plants of the resistant biotypes survived unaffected. The high correlation between the plants that survived herbicide soaking treatments and survival from a subsequent foliar herbicide spray confirmed that the discrimination of the resistant and the susceptible biotypes by seed soaking method was reliable. This method is 4-5 weeks quicker than the conventional foliar spray method and minimizes sources of errors that are likely to occur with that method.


Plant Protection Quarterly (2002) 17 (1) 35-38.