Characterisation of Avena fatua populations with resistance to multiple herbicides

Abstract

Avena fatua (wild oat) populations with resistance (R) to one or more herbicides have been described in numerous cropping systems worldwide. We previously reported that the R3 and R4 wild oat populations from Montana, USA, were resistant to four herbicides representing three different modes of action: tralkoxydim [acetyl-CoA carboxylase (ACCase] inhibitor), imazamethabenz and flucarbazone [acetolactate synthase (ALS) inhibitors] and difenzoquat (growth inhibitor). We now quantify resistance levels of these populations to triallate [very long chain fatty acid (VLCFA) biosynthesis inhibitor], pinoxaden (ACCase inhibitor) and paraquat (photosystem I inhibitor). Glasshouse doseresponse experiments showed that, compared with the means of two susceptible (S) populations, the R3 and R4 populations were 17.5-and 18.1-fold more resistant to triallate, 3.6-and 3.7-fold more resistant to pinoxaden, respectively, and 3.2-fold (R3) more resistant to paraquat. Pre-treatment of R plants with the cytochrome P450 inhibitor malathion partially reversed the resistance phenotype for flucarbazone (both populations), imazamethabenz (R4), difenzoquat (R4) and pinoxaden (R3), but not for tralkoxydim, fenoxaprop-P-ethyl or triallate. Target site point mutations known to confer resistance to ALS or ACCase inhibitors were not detected via DNA sequencing and allele-specific PCR assays in R plants, suggesting the involvement of non-target site resistance mechanism(s) for these herbicides. Together, our results complete the initial characterisation of wild oat populations that are resistant to seven (R3) or six (R4) herbicides from five or four mode of action families respectively.

Intensive herbicide use has selected for constitutively elevated levels of stress‐responsive mRNAs and proteins in multiple herbicide‐resistant Avena fatua L

“…Field‐collected seeds (about 90% of which were resistant to 60 g a.i. ha −1 pinoxaden, data not shown) were subjected to two generations of recurrent group selection (50 plants each generation) by spraying with the same dose of pinoxaden, after which 100% of plants were confirmed to be homozygous resistant to pinoxaden via dose response experiments . From each generation of 50 plants, all seeds were harvested and a random selection of 50 seeds was used to initiate five additional generations without herbicide selection to homogenize the genetic background.…”

“…From each generation of 50 plants, all seeds were harvested and a random selection of 50 seeds was used to initiate five additional generations without herbicide selection to homogenize the genetic background. The HS1 population was derived from seeds collected from untreated border plants in an adjacent field, grown for seven generations as described for MHR4 except without herbicide selection, and was subsequently confirmed to be 100% susceptible to the herbicides used in these studies . A second susceptible population HS2 used for crossing studies (see below) is the highly inbred nondormant SH430 line used in seed dormancy research .…”

“…HR species from the Poaceae family are over‐represented among ‘the world's worst weed families’, and HR A. fatua populations probably have a greater worldwide economic impact than those of any other species . We recently described the MHR3 and MHR4 A. fatua populations from northcentral Montana that are resistant to the acetyl‐CoA carboxylase (ACCase) inhibitors fenoxaprop‐P‐ethyl, tralkoxydim and pinoxaden, the acetolactate synthase (ALS) inhibitors imazamethabenz‐methyl and flucarbazone‐sodium (flucarbazone hereafter), the growth inhibitor difenzoquat, the photosystem I inhibitor paraquat (MHR3 only) and the very long chain fatty acid biosynthesis inhibitor triallate, with resistant/susceptible ED 50 ratios ranging from 1.4 to 57 . Additional herbicide screens show that MHR3 and MHR4 are resistant to US field use rates of quizalofop‐P‐ethyl, fluazifop‐P‐butyl, diclofop‐methyl and prosulfocarb (Dyer et al ., unpublished).…”

“…MHR3 and MHR4 resistance to ALS‐ and ACCase‐inhibiting herbicides is not due to known target site mutations, and the cytochrome P450 monooxygenase (P450) inhibitor malathion partially reversed the resistance phenotype for flucarbazone (both populations), imazamethabenz (MHR4), difenzoquat (MHR4) and pinoxaden (MHR3), indicating the involvement of NTSR mechanisms. NTSR evolves gradually under the strong selection imposed by herbicides, appears to be controlled by multiple alleles and is conferred by one or more constitutive and/or induced physiological mechanisms .…”

Selection and evaluation of potential reference genes for gene expression analysis in Avena fatua

“…At the same time, it is also a malignant weed that harms wheat, oilseed rape, and other crops in China and has developed serious resistance to herbicides all over the world (Cavan et al 2001). In recent years, qPCR has been widely used to quantify gene expression levels in diverse studies of A. fatua, such as studies of herbicide resistance and ecological adaption (Li et al 2009;Cruzhipolito et al 2011;Keith et al 2015). Some studies have shown that at least two or three reference genes should be used to achieve accurate normalisation (Thellin et al 1999;Vandesompele et al 2002).…”