Identification ofAvena fatuapopulations resistant to imazamethabenz, flamprop, and fenoxaprop-P

Abstract

Three Avena fatua (wild oat) populations resistant to imazamethabenz, flamprop, and fenoxaprop-P were identified from the northwest agricultural region of Manitoba, Canada. These populations were identified after producer reports of failure of imazamethabenz to provide satisfactory control in the field. Although these A. fatua populations had previously been exposed to other herbicides, primarily ACCase inhibitors, imazamethabenz had never before been applied. In growth room experiments, resistant (R) plants were 7.2 and 8.7 times more resistant to imazamethabenz and flamprop, respectively, than susceptible (S) plants, as measured by the ratio of dosages required to inhibit shoot dry matter accumulation by 50% (GR50 R/S). The three populations did not differ significantly (P < 0.05) in levels of resistance to imazamethabenz. Similarly, the populations did not differ in levels of resistance to flamprop. The populations differed in their response to fenoxaprop-P; levels of resistance for two populations were 2.0-fold, while the remaining population was 2.9-fold. An experiment conducted in 1995 in one of the infested fields confirmed multiple herbicide resistance, with A. fatua panicle numbers in August being 36, 128, and 44% of untreated controls at recommended dosages of imazamethabenz, flamprop, and fenoxaprop-P, respectively. Three additional populations of A. fatua with multiple herbicide resistance from other areas of Manitoba were identified in a 1996 field experiment. For the six A. fatua populations in the 1996 experiment with multiple herbicide resistance, panicle numbers expressed as a percentage of the untreated controls varied from 44 to 77% for imazamethabenz, 57 to 83% for flamprop, and 43 to 88% for fenoxaprop-P (commercially recommended dosage of each herbicide). Multiple herbicide resistance in A. fatua is not rare; screening of A. fatua seed samples from across Manitoba and Saskatchewan has identified a number of additional R populations. The evolution of herbicide resistance in the absence of direct selection is a very serious development as producers with multiple herbicide resistance in A. fatua are left with a very limited number of herbicide options for selective control in crops commonly grown in western Canada.

Cross-resistance patterns of winter wild oat (Avena ludoviciana) populations to ACCase inhibitor herbicides

“…The first case of ACCase inhibitor resistance in wild oat was reported in Western Australia in 1985 (Heap 2015) followed by many other reports thereafter (e.g., Devine 1994, Seefeldt et al 1994;Murray et al 1996;Beckie et al 2002). Cross-or multiple-resistance patterns were also characterized in wild oat populations in some studies (Kern et al 1996;Friesen et al 2000;Uludag et al 2008).…”

Inheritance of multiple herbicide resistance in wild oat (Avena fatua L.)

“…Producers collected seed of the multiple herbicide resistant wild oat populations UMWO12-01 and UMWO12-03 from wild oat plants/patches in their fields in mid-August 1994 and 1995, respectively (Friesen et al 2000). Plants grown from each population were screened with 100 g a.i.…”

“…These growth stages follow commercial label recommendations. Herbicide dosages used in this study were based on a previous study using these multiple herbicide resistant wild oat populations (Friesen et al 2000). These herbicide dosages provided a clear distinction between resistant (R) and susceptible (S) plants.…”

“…This type of evolution of multiple resistance is more probable in highly outcrossing species. The relatively high number of populations of wild oat that have exhibited resistance to multiple herbicide modes of action in the absence of specific selection (i.e., no use of a specific herbicide) suggests that multiple resistance due to enhanced metabolism controlled by a single gene is more likely than accumulation of multiple resistance genes (Somody et al 1984;Beckie et al 1999;Friesen et al 2000). The probability of multiple mechanisms of resistance in an unselected population is the product of the probabilities of natural resistance (resulting from mutations) to each herbicide and therefore should be rare in the absence of selection (Wrubel and Gressel 1994).…”

“…The two multiple herbicide resistant wild oat populations used in this study originated from the northwestern agricultural region (Swan River region) of Manitoba, Canada (Friesen et al 2000). The populations were first identified when producers reported unsatisfactory control of wild oat in spring wheat crops sprayed with imazamethabenz-methyl (imazamethabenz).…”